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synfiniway synfiniway middleware virtualised framework created provides uniform global view resources within department company company suppliers virtualised framework service-oriented meaning applications run services system-independent view applications several applications linked workflow data exchange applications participating workflow implicitly managed framework synfiniway platform-independent allowing almost distributed heterogeneous platform linked virtualised framework virtualised framework implemented synfiniway installing component specific software agents systems framework three major types components synfiniway components based java deployed multi-platform environment example framework two neighbourhoods shown figure adding removing components automatically detected framework synfiniway meta-scheduler automatically adjusts changes service manager service availability synfiniway geared towards service management means application command utilised defined service published synfiniway framework simple complex tasks abstracted services execution using abstracted services user easily run applications commands regardless complex may underlying infrastructure required provide form virtualisation computing resources since user need aware service available run technical business process created linking services workflow workflows synfiniway based wfmc version 1.0 workflow defines one tasks executed given execution logic branch loop conditional synfiniway supports multi-instance tasks run service multiple times concurrently also supports workflow workflows whereby workflow executed task higher level workflow files needed service automatically transferred computer executing service user freed manage file transfers file transfer mechanism used allowing files transferred directly source target computer system going number firewalls source target without stored intermediary systems mechanism uses shortest path transferring files target computer source synfiniway employs meta-scheduling capability optimizing computational workloads combining multiple distributed resource managers organisation using single aggregated view allowing batch jobs directed best location execution using local resource managers lsf pbspro sge loadleveler synfiniway able schedule execute services deployed mixed interlinked set local resource managers
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Distributed computing architecture
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arrayed waveguide grating arrayed waveguide gratings awg commonly used optical de multiplexers wavelength division multiplexed wdm systems devices capable multiplexing large number wavelengths single optical fiber thereby increasing transmission capacity optical networks considerably devices based fundamental principle optics light waves different wavelengths interfere linearly means channel optical communication network makes use light slightly different wavelength light large number channels carried single optical fiber negligible crosstalk channels awgs used multiplex channels several wavelengths onto single optical fiber transmission end also used demultiplexers retrieve individual channels different wavelengths receiving end optical communication network conventional silica-based awgs schematically shown figure planar lightwave circuits fabricated depositing doped undoped layers silica silicon substrate awgs consist number input 1 output 5 couplers free space propagation region 2 4 grating waveguides 3 grating consists large number waveguides constant length increment δl light coupled device via optical fiber 1 connected input port light diffracting input waveguide coupler/slab interface propagates free-space region 2 illuminates grating gaussian distribution wavelength light coupled grating waveguides 3 undergoes constant change phase attributed constant length increment grating waveguides light diffracted waveguide grating interferes constructively gets refocused output waveguides 5 spatial position output channels wavelength dependent array phase shift
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Internet protocols
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layer four traceroute layer four traceroute lft fast multi-protocol traceroute engine also implements numerous features including number lookups regional internet registries reliable sources loose source routing firewall load balancer detection etc lft best known use network security practitioners trace route destination host many configurations packet-filters firewalls detect network connectivity performance latency problems lft sends various tcp syn fin probes differing van jacobson udp-based method udp probes utilizing ip protocol time live field attempts elicit icmp time_exceeded response gateway along path host lft also listens various tcp udp icmp messages along way assist network managers ascertaining per-protocol heuristic routing information optionally retrieve various information networks traverses operation layer four traceroute described detail several prominent security books codice_1 command first appeared 1998 codice_2 renamed result confusion fast fourier transforms lft stands layer four traceroute results often referred layer four trace
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Computer security
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list free electronics circuit simulators electronic circuit simulators distributed free software license available several sources several computing platforms
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Programming language topics
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infrascale infrascale draas disaster-recovery-as-a-service data protection company based el segundo california founded 2011 company headquartered el segundo california offices australia india ukraine 16 datacenters around world including united states canada australia united kingdom india ukraine south africa 2014 company acquired eversync solutions inc offer cloud on-premises backup archiving disaster recovery solutions program received awards various analyst firms publications 2017 redmond channel partners named infrascale best ransomware solution also 2017 gartner named infrascale leader draas magic quadrant 2016 gartner named infrascale visionary disaster recovery magic quadrant 2015 business continuity cool vendor crn named infrascale one 20 coolest cloud storage vendors 2016 cloud 100 features include failover continuous data protection unlimited versioning archiving integrated local backup remote wipe geo-locate military-grade security available direct-to-cloud offering local on-premises appliance january 17 2017 announced partnership google cloud platform deliver faster failover infrascale comes two versions infrascale 100 channel focused concentrates heavily selling resellers managed service providers infrascale products include several features targeted protecting data
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Distributed computing architecture
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systemstarter systemstarter system program mac os x started mac os x bsd-style init prior mac os x v10.4 launchd mac os x v10.4 later releases starts system processes specified set property lists systemstarter originally written wilfredo sanchez mac os x mac os x v10.4 deprecated favor launchd kept system start system processes yet converted use launchd systemstarter appears removed os x 10.10 later
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Operating systems
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cyber intelligence sharing protection act cyber intelligence sharing protection act cispa 112th congress 113th congress 114th congress proposed law united states would allow sharing internet traffic information u.s. government technology manufacturing companies stated aim bill help u.s. government investigate cyber threats ensure security networks cyberattacks legislation introduced november 30 2011 representative michael rogers r-mi 111 co-sponsors passed house representatives april 26 2012 passed u.s. senate president barack obama advisers argued bill lacks confidentiality civil liberties safeguards white house said would veto february 2013 house reintroduced bill passed united states house representatives april 18 2013 stalled voted upon senate july 10 2014 similar bill cybersecurity information sharing act cisa introduced senate january 2015 house reintroduced bill bill referred committee intelligence february 2 2015 subcommittee crime terrorism homeland security investigations subcommittee constitution civil justice see come house vote december 2015 version cispa hidden total federal budget cispa garnered favor corporations lobbying groups microsoft facebook ibm united states chamber commerce look simple effective means sharing important cyber threat information government however criticized advocates internet privacy civil liberties electronic frontier foundation american civil liberties union free press fight future avaaz.org well various conservative libertarian groups including competitive enterprise institute techfreedom freedomworks americans limited government liberty coalition american conservative union groups argue cispa contains limits government may monitor private individual ’ internet browsing information additionally fear new powers could used spy general public rather pursue malicious hackers critics saw wording included cispa second attempt protect intellectual property stop online piracy act taken table congress met opposition intellectual property theft initially listed bill possible cause sharing web traffic information government though removed subsequent drafts cispa amendment national security act 1947 currently contain provisions pertaining cybercrime adds provisions act describing cyber threat intelligence information possession element intelligence community directly pertaining vulnerability threat system network government private entity including information pertaining protection system network either efforts degrade disrupt destroy system network addition cispa requires director national intelligence establish procedures allow intelligence community elements share cyber threat intelligence private-sector entities encourage sharing intelligence april 16 2012 press release house representatives permanent select committee intelligence announced approval several amendments cispa including addition new provision permit federal lawsuits government violation restrictions placed government ’ use voluntarily shared information including important privacy civil liberties protections contained bill inclusion anti-tasking provision explicitly prohibit government conditioning sharing cyber threat intelligence sharing private sector information government prevention government using information lawful purpose unless government already significant cybersecurity national security purpose using information relevant provisions also clarified focus fact bill designed protect unauthorized access networks systems including unauthorized access aimed stealing private government information addition already collected cyberthreat data also used investigate imminent threat bodily harm individual exploitation minor bringing bill line existing law codified patriot act protect children act two conditions already allow protected entities share data voluntarily united states government law enforcement agencies national center missing exploited children bill sponsors mike rogers dutch ruppersberger chairman ranking member house intelligence committee respectively said april 25 2012 obama administration opposition mostly based lack critical infrastructure regulation something outside jurisdiction intelligence committee also since introduced package amendments legislation address nearly every single one criticisms leveled administration particularly regarding privacy civil liberties americans due opposition bill experienced co-sponsors planning amend bill address many concerns opponents—including limiting scope narrower definition cyber-threats stating theft intellectual property refers theft research development addition penalties private companies government uses data cispa purposes unrelated cyberthreats however sharan bradford franklin constitution project states although appreciate intelligence committee efforts improve bill willingness engage dialogue privacy advocates changes current draft come close addressing civil liberties threats posed bill proposals would actually make cispa worse therefore congress pass cispa rainey reitman electronic frontier foundation states date authors bill unresponsive criticisms offering amendments largely cosmetic dismissing grave concerns bill could undermine core privacy rights everyday internet users rep. mike rogers characterized growing protests cispa 'turbulence vowed push floor vote without radical changes kendall burman center democracy technology states authors cispa made positive changes recently unfortunately none changes gets heart privacy concerns internet users advocacy groups expressed april 2012 office management budget executive office president united states released statement strongly opposing current bill recommending veto april 26 2012 house representatives passed cispa february 13 2013 united states representative mike rogers reintroduced cispa bill 113th congress h.r 624 april 18 2013 house representatives passed h.r 624 senate reportedly refused vote measure drafting competing legislation july 10 2014 similar bill cybersecurity information sharing act cisa introduced senate full list seen house.gov site full list seen house.gov site cispa supported several trade groups containing eight hundred private companies including business software alliance ctia – wireless association information technology industry council internet security alliance national cable telecommunications association national defense industrial association techamerica united states chamber commerce addition individual major telecommunications information technology companies like ibm intel oracle corporation symantec verizon google taken public position bill shown previous support says support idea believe bill needs work leading google yahoo microsoft executives also executive council technet tech trade group sent letter supporting cispa april 2013 dubbed stop cyber spying week starting april 16 2012 many civil liberties groups advocates raised awareness cispa twitter campaign hash-tags cispa congresstmi including limited constitution project american civil liberties union electronic frontier foundation center democracy technology demand progress fight future free press reporters without borders sunlight foundation techfreedom anonymous hacktivist group criticized bill called internet blackout day protest bill date blackout april 22 2013 since legislation must pass house senate within congress anything introduced 112th earlier congresses pass chambers
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Computer security
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drive letter access drive letter access dla discontinued commercial packet writing application microsoft windows operating system allows optical disc data storage devices used manner similar floppy disks dla packet writing technology cd dvd media uses udf file system dla compatible windows vista newer although patch exists fix issue windows vista roxio burn introduced april 30 2009 replacement dla remedies compatibility issues internet explorer 8 dla originally developed veritas software later sold sonic solutions 2002 common shipped majority cd dvd recording drives dla came custom oem version branded drive also pc systems dell hp ibm sony toshiba came dla pre-installed oem version often available download specific computer system windows vista support dla either dropped replaced similar product like drag-to-disc use optical medium cd-r cd-rw dvd±r dvd±rw like floppy drive necessary utilize technique called packet writing formatting optical media possible write data small packets hence name “ packet writing. ” optical drive unit support ability write small units modern cd dvd recording drives way possible save files onto optical media well change rename delete copy files separately onto media without packet writing optical media like above-mentioned would written one big block like disc dao session sao track tao media types normally support sectors formatting packet writing medium sectored blocks written individually preferred file system universal disk format udf versions 1.50 onward also used dla packet writing required writing dvd-ram dvd-ram media already sectored seen looking surface empty dvd-ram disc hardware logic dvd-ram capable drives supports sectored read/write operations required dvd-ram standard however windows 2000 dla also add support dvd-ram together udf file system windows xp dla add udf support dla also supports mount rainier standard mrw capable drives windows xp dla provide functionality well udf support windows xp first windows operating system support dvd-ram windows vista first windows operating system support full udf functionality udf version 2.50 full support meaning read write operations mount rainier dla available microsoft windows operating systems english language note oem versions officially support windows 2000 xp however dla also runs older versions windows like windows 98 second edition windows well windows nt 4.0 patch required windows vista compatibility works retail trial version one exception dell oem version instead patching dla simply install drag-to-disc replacement techniques used dla competing applications
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Computer file systems
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nashorn javascript engine nashorn javascript engine developed java programming language oracle based da vinci machine jsr 292 released java 8 project announced first jvm language summit july 2011 confirmed javaone october 2011 november 21 2012 oracle formally announced open sourcing nashorn source openjdk repository project aim allow embedding javascript java applications via jsr-223 develop standalone javascript applications december 21 2012 oracle announced nashorn source publicly released openjdk repository release java 11 nashorn deprecated likely removed jdk later time graalvm suggested replacement nashorn nahss-horn german translation rhinoceros play words rhino name javascript engine implemented java provided mozilla foundation latter gets name animal cover javascript book o'reilly media according oracle benchmarks nashorn performance several orders magnitude faster alternative rhino javascript engine
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Programming language topics
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vhdl vhdl vhsic-hdl high speed integrated circuit hardware description language hardware description language used electronic design automation describe digital mixed-signal systems field-programmable gate arrays integrated circuits vhdl also used general purpose parallel programming language starting 1983 vhdl originally developed behest u.s department defense order document behavior asics supplier companies including equipment standard mil-std-454n requirement 64 section 4.5.1 asic documentation vhdl explicitly requires documentation microelectronic devices vhdl idea able simulate asics information documentation obviously attractive logic simulators developed could read vhdl files next step development logic synthesis tools read vhdl output definition physical implementation circuit due department defense requiring much syntax possible based ada order avoid re-inventing concepts already thoroughly tested development ada vhdl borrows heavily ada programming language concepts syntax initial version vhdl designed ieee standard ieee 1076-1987 included wide range data types including numerical integer real logical bit boolean character time plus arrays codice_1 called codice_2 codice_3 called string problem solved edition however multi-valued logic signal drive strength none weak strong unknown values also considered required ieee standard 1164 defined 9-value logic types scalar codice_4 vector version codice_5 resolved subtype codice_6 parent type codice_4 typed signals allow multiple driving modeling bus structures whereby connected resolution function handles conflicting assignments adequately updated ieee 1076 1993 made syntax consistent allowed flexibility naming extended codice_3 type allow iso-8859-1 printable characters added codice_9 operator etc minor changes standard 2000 2002 added idea protected types similar concept class c++ removed restrictions port mapping rules addition ieee standard 1164 several child standards introduced extend functionality language ieee standard 1076.2 added better handling real complex data types ieee standard 1076.3 introduced signed unsigned types facilitate arithmetical operations vectors ieee standard 1076.1 known vhdl-ams provided analog mixed-signal circuit design extensions standards support wider use vhdl notably vital vhdl initiative towards asic libraries microwave circuit design extensions june 2006 vhdl technical committee accellera delegated ieee work next update standard approved called draft 3.0 vhdl-2006 maintaining full compatibility older versions proposed standard provides numerous extensions make writing managing vhdl code easier key changes include incorporation child standards 1164 1076.2 1076.3 main 1076 standard extended set operators flexible syntax case generate statements incorporation vhpi vhdl procedural interface interface c/c++ languages subset psl property specification language changes improve quality synthesizable vhdl code make testbenches flexible allow wider use vhdl system-level descriptions february 2008 accellera approved vhdl 4.0 also informally known vhdl 2008 addressed 90 issues discovered trial period version 3.0 includes enhanced generic types 2008 accellera released vhdl 4.0 ieee balloting inclusion ieee 1076-2008 vhdl standard ieee 1076-2008 published january 2009 ieee standard 1076 defines vhsic hardware description language vhdl originally developed contract f33615-83-c-1003 united states air force awarded 1983 team intermetrics inc. language experts prime contractor texas instruments chip design experts ibm computer system design experts language undergone numerous revisions variety sub-standards associated augment extend important ways 1076 continues milestone design electronic systems vhdl commonly used write text models describe logic circuit model processed synthesis program part logic design simulation program used test logic design using simulation models represent logic circuits interface design collection simulation models commonly called testbench vhdl simulator typically event-driven simulator means transaction added event queue specific scheduled time e.g signal assignment occur 1 nanosecond event added queue time +1ns zero delay also allowed still needs scheduled cases delta delay used represent infinitely small time step simulation alters two modes statement execution triggered statements evaluated event processing events queue processed vhdl constructs handle parallelism inherent hardware designs constructs processes differ syntax parallel constructs ada tasks like ada vhdl strongly typed case sensitive order directly represent operations common hardware many features vhdl found ada extended set boolean operators including nand vhdl file input output capabilities used general-purpose language text processing files commonly used simulation testbench stimulus verification data vhdl compilers build executable binaries case might possible use vhdl write testbench verify functionality design using files host computer define stimuli interact user compare results expected however designers leave job simulator relatively easy inexperienced developer produce code simulates successfully synthesized real device large practical one particular pitfall accidental production transparent latches rather d-type flip-flops storage elements one design hardware vhdl ide fpga implementation xilinx ise altera quartus synopsys synplify mentor graphics hdl designer produce rtl schematic desired circuit generated schematic verified using simulation software shows waveforms inputs outputs circuit generating appropriate testbench generate appropriate testbench particular circuit vhdl code inputs defined correctly example clock input loop process iterative statement required final point vhdl model translated gates wires mapped onto programmable logic device cpld fpga actual hardware configured rather vhdl code executed form processor chip key advantage vhdl used systems design allows behavior required system described modeled verified simulated synthesis tools translate design real hardware gates wires another benefit vhdl allows description concurrent system vhdl dataflow language unlike procedural computing languages basic c assembly code run sequentially one instruction time vhdl project multipurpose created calculation block used many projects however many formational functional block parameters tuned capacity parameters memory size element base block composition interconnection structure vhdl project portable created one element base computing device project ported another element base example vlsi various technologies big advantage vhdl compared original verilog vhdl full type system designers use type system write much structured code especially declaring record types vhdl design consists minimum entity describes interface architecture contains actual implementation addition designs import library modules designs also contain multiple architectures configurations simple gate vhdl would look something like notice codice_10 stands register transfer level design example may seem verbose hdl beginners many parts either optional need written generally simple functions like part larger behavioral module instead separate module something simple addition use elements codice_4 type might first seem overkill one could easily use built-in codice_1 type avoid library import beginning however using 9-valued logic codice_13 codice_14 codice_15 codice_16 codice_17 codice_18 codice_19 codice_20 codice_21 instead simple bits 0,1 offers powerful simulation debugging tool designer currently exist hdl examples follow see vhdl code written compact form however experienced designers usually avoid compact forms use verbose coding style sake readability maintainability another advantage verbose coding style smaller amount resources used programming programmable logic device cpld vhdl frequently used two different goals simulation electronic designs synthesis designs synthesis process vhdl compiled mapped implementation technology fpga asic many fpga vendors free inexpensive tools synthesize vhdl use chips asic tools often expensive constructs vhdl suitable synthesis example constructs explicitly deal timing codice_22 synthesizable despite valid simulation different synthesis tools different capabilities exists common synthesizable subset vhdl defines language constructs idioms map common hardware many synthesis tools ieee 1076.6 defines subset language considered official synthesis subset generally considered best practice write idiomatic code synthesis results incorrect suboptimal non-standard constructs multiplexer 'mux usually called simple construct common hardware design example demonstrates simple two one mux inputs codice_23 codice_24 selector codice_25 output codice_14 note many ways express mux vhdl transparent latch basically one bit memory updated enable signal raised many ways expressed vhdl d-type flip-flop samples incoming signal rising falling edge clock example asynchronous active-high reset samples rising clock edge another common way write edge-triggered behavior vhdl 'event signal attribute single apostrophe written signal name name attribute vhdl also lends one-liners useful signals registers driven process reset following example up-counter asynchronous reset parallel load configurable width demonstrates use 'unsigned type type conversions 'unsigned 'std_logic_vector vhdl generics generics close arguments templates traditional programming languages like c++ complex counters may add if/then/else statements within codice_27 add functions count enables stopping rolling count value generating output signals like terminal count signals etc care must taken ordering nesting controls used together order produce desired priorities minimize number logic levels needed large subset vhdl translated hardware subset known non-synthesizable simulation-only subset vhdl used prototyping simulation debugging example following code generate clock frequency 50 mhz example used drive clock input design simulation however simulation-only construct implemented hardware actual hardware clock generated externally scaled internally user logic dedicated hardware simulation-only constructs used build complex waveforms short time waveform used example test vectors complex design prototype synthesizer logic implemented future commercial
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Programming language topics
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comparison object-relational mapping software table shows comparison notable orm software products currently available
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Databases
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xsgi xsgi silicon graphics sgi implementation x window system x11 server irix-based graphical workstations servers xsgi released 1991 irix 4.0 sgi indigo workstation work xsgi began may 1989 tom paquin left ibm join sgi integrate x window system sgi iris gl interface paquin recruited set software engineers experienced x server implementation jeff weinstein erik fortune paul shupak john giannandrea peter daifuku michael toy todd newman spence murray dave spalding graphics hardware designed silicon graphics provided accelerated rendering access graphics hardware commands rather memory-mapped framebuffers manipulated cpu made monochrome framebuffer mfb color framebuffer cfb device-dependent rendering layers supplied mit x11 sampler server inappropriate silicon graphics hardware jeff weinstein developed framebuffer nfb device-dependent rendering layer support silicon graphics style hardware access sco later incorporated nfb layer x server porting layer silicon graphics hardware included overlay planes provide hardware overlay initial efforts todd newman implement overlay plane support xsgi eventually led peter daifuku fully functional support overlay planes daifuku separated notion window visibility clipping region window renderable clipping region previously mit x sample server treated two clipping regions identical region xsgi advertises overlay planes x11 visuals overlay characteristics described server_overlay_visuals convention erik fortune developed x keyboard extension xkb xsgi xsgi supported x11 iris gl opengl display postscript pex phigs rendering models
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Computer architecture
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comparison algol 68 c++ c++ n't algol 68 n't assigning values a68 codice_1 variable automatic type tagged variable pulling value back syntactically awkward conformity-clause required algol 68 example c/c++ example net effect type-tagging algol68 strong typing half encroaches codice_1 new mode type may declared using codice_3 declaration similar effect following c++ code const int max=99 typedef struct newtype 9+1 max+1 note algol 68 newtype name appears left equality notably construction made read left right without regard priorities
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Programming language topics
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grand central dispatch grand central dispatch gcd technology developed apple inc. optimize application support systems multi-core processors symmetric multiprocessing systems implementation task parallelism based thread pool pattern fundamental idea move management thread pool hands developer closer operating system developer injects work packages pool oblivious pool architecture model improves simplicity portability performance gcd first released mac os x 10.6 also available ios 4 name grand central dispatch reference grand central terminal source code library provides implementation gcd services libdispatch released apple apache license september 10 2009 ported freebsd operating system starting freebsd 8.1 midnightbsd 0.3-current includes libdispatch without blocks support linux solaris support provided within upstream trunk order develop support windows currently two forks exist opensource.mlba-team.de github apple port libdispatch.dll windows shipped safari itunes sdk provided gcd works allowing specific tasks program run parallel queued execution depending availability processing resources scheduling execute available processor cores referred routing apple task expressed either function block blocks extension syntax c c++ objective-c programming languages encapsulate code data single object way similar closure gcd still used environments blocks available grand central dispatch still uses threads low level abstracts away programmer need concerned many details tasks gcd lightweight create queue apple states 15 instructions required queue work unit gcd creating traditional thread could easily require several hundred instructions task grand central dispatch used either create work item placed queue assign event source task assigned event source work unit made block function event triggers work unit placed appropriate queue described apple efficient creating thread whose sole purpose wait single event triggering dispatch framework declares several data types functions create manipulate two examples demonstrate use grand central dispatch found john siracusa ars technica snow leopard review initially document-based application method called codice_1 may something like count number words paragraphs document normally would quick process may executed main thread without user noticing delay pressing button results showing document large analysis takes long time execute main thread wait function finish takes long enough user notice application may even beachball solution seen call codice_2 placed inside block placed one global concurrent queues finished running codice_2 new block placed main queue main thread application runs updates gui necessary gui updated main thread making two small changes developer avoided potential stall application seen user allowed application make better use hardware resources second example parallelising loop code runs codice_4 function codice_5 times assigning result element array codice_6 calls summarize array loop ended unfortunately work computed sequentially may need assuming do_work n't rely results calls made reason calls made concurrently would done gcd codice_7 runs block passed codice_5 times placing invocation global queue passing block invocation different number 0 codice_5-1 allow os spread work sees fit choosing optimal number threads run current hardware system load codice_7 return blocks places given queue completed execution guaranteed work inside original loop completed calling codice_11 programmers create serial queues tasks know must run serially may executed separate thread new queue would created like care must taken avoid dispatched block queue synchronously placing another block queue guaranteed deadlock code might following gcd used throughout macos beginning 10.6 snow leopard apple encouraged adoption macos application developers freebsd developer robert watson announced first adaptation major open source application apache http server use gcd via apache gcd mpm multi-processing module may 11 2010 order illustrate programming model integrate gcd existing large-scale multi-threaded applications announcement observed gcd mpm one third half number lines threaded mpms gcd implemented libdispatch support pthreads non-posix extensions developed apple apple changed interface since inception os x 10.5 official launch gcd 10.6 mountain lion 10.8 recently mavericks 10.9 latest changes involve making code supporting pthreads user mode kernel private kernel pthread support reduced shims actual implementation moved separate kernel extension
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Operating systems
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value computer science computer science value representation entity manipulated program members type values type value variable given corresponding mapping environment languages assignable variables becomes necessary distinguish r-value contents l-value location variable declarative high-level languages values referentially transparent means resulting value independent location sub- expression needed compute value stored contents location bits whether 1 0 interpretation significant languages use idea l-values r-values deriving typical mode evaluation left right hand side assignment statement l-value refers object persists beyond single expression r-value temporary value persist beyond expression uses notion l-values r-values introduced combined programming language cpl notions expression r-value l-value r-value/l-value analogous parameter modes input parameter value output parameter assigned input/output parameter value assigned though technical details differ contexts languages many languages notably c family l-values storage addresses programmatically accessible running program e.g. via address-of operator like c/c++ meaning variables dereferenced references certain memory location r-values l-values see non-l-values—a term used distinguish l-values consider c expression executed computer generates integer value 13 program explicitly designated computer 13 stored expression non l-value hand c program declares variable x assigns value 13 x expression value 13 l-value c term l-value originally meant something could assigned hence name indicating left side assignment operator since reserved word constant added language term 'modifiable l-value c++11 special semantic-glyph exists denote use/access expression address compiler i.e. address retrieved using address-of operator run-time program see use move semantics type reference applied r-values including non-l-values well l-values processors provide one instructions take immediate value sometimes referred immediate short immediate value stored part instruction employs usually load add subtract register parts instruction opcode destination latter may implicit non-immediate value may reside register stored elsewhere memory requiring instruction contain direct indirect address e.g. index register address value l-value expression designates refers object non-modifiable l-value addressable assignable modifiable l-value allows designated object changed well examined r-value expression non-l-value expression l-value one example immediate value look consequently addressable.. value virtually kind data given data type instance string digit single letter processors often support one size immediate data e.g 8 16 bit employing unique opcode mnemonic instruction variant programmer supplies data value fit assembler issues range error message assemblers allow immediate value expressed ascii decimal hexadecimal octal binary data thus ascii character byte order strings may differ processors depending assembler computer architecture
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Programming language topics
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database refactoring database refactoring simple change database schema improves design retaining behavioral informational semantics database refactoring change way data interpreted used fix bugs add new functionality every refactoring database leaves system working state thus causing maintenance lags provided meaningful data exists production environment database refactoring conceptually difficult code refactoring code refactorings need maintain behavioral semantics database refactorings also must maintain informational semantics refactor database schema one several reasons examples database refactoring process database refactoring act applying database refactorings evolve existing database schema database refactoring core practice evolutionary database design three considerations need taken account
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Databases
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cpu card cpu card printed circuit board pcb contains central processing unit cpu computer cpu cards specified cpu clock frequency bus type well features applications built card cpu cards include peripheral component interconnect pci cards modular pc cards industry standard architecture isa cards pci extensions instrumentation pxi cards embedded technology extended etx cards many others cpu cards often used expand memory speed bandwidth embedded applications existing computer system pc cards typically used expand system ’ embedded applications pc cards include modules audio video applications data communications embedded storage pxi cards used data acquisition control systems making suitable real-time measurement applications etx cards used industrial applications augment computer system ’ embedded applications etx cards contain functionality necessary run pc compact space cpu cards used augment existing computer backplanes typically isa pci connectors plugged backplane without additional configuration cpu cards use computer backplanes typically half-sized cpu card contains pc functionality communicates cards plugged backplane computer bus cpu cards may also called expansion cards expansion boards offer variety embedded applications modems wireless networking graphics video controllers raid controllers
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Computer architecture
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udp hole punching udp hole punching commonly used technique employed network address translation nat applications maintaining user datagram protocol udp packet streams traverse nat nat traversal techniques typically required client-to-client networking applications internet involving hosts connected private networks especially peer-to-peer direct client-to-client dcc voice internet protocol voip deployments udp hole punching establishes connectivity two hosts communicating across one network address translators typically third-party hosts public transit network used establish udp port states may used direct communications communicating hosts port state successfully established hosts communicating port state may maintained either normal communications traffic prolonged absence thereof keep-alive packets usually consisting empty udp packets packets minimal non-intrusive content udp hole punching method establishing bidirectional udp connections internet hosts private networks using network address translators technique applicable scenarios types nats nat operating characteristics standardized hosts network connectivity inside private network connected via nat internet typically use session traversal utilities nat stun method interactive connectivity establishment ice determine public address nat communications peers require process another host public network used establish port mapping udp port state assumed valid direct communication application hosts since udp state usually expires short periods time range tens seconds minutes udp port closed process udp hole punching employs transmission periodic keep-alive packets renewing life-time counters udp state machine nat udp hole punching work symmetric nat devices also known bi-directional nat tend found large corporate networks symmetric nat nat mapping associated connection well-known stun server restricted receiving data well-known server therefore nat mapping well-known server sees useful information endpoint somewhat elaborate approach hosts start sending using multiple attempts restricted cone nat first packet host blocked nat device record sent packet machine let packets coming ip address port number technique widely used peer-to-peer software voice internet protocol telephony also used assist establishment virtual private networks operating udp technique sometimes extended transmission control protocol tcp connections though less success tcp connection streams controlled host os application sequence numbers selected randomly thus nat device performs sequence-number checking consider packets associated existing connection drop let b two hosts private network n n two nat devices globally reachable ip addresses eip eip respectively public server well-known globally reachable ip address
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Computer security
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net.data net.data programming language ibm used largely database-backed web applications
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Programming language topics
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night shift software night shift built software feature ios macos introduced ios ios 9.3 macos macos sierra 10.12.4 feature changes color temperature display towards yellowish part color spectrum reduces blue light screen apple claims feature may help users better night sleep filtering blue wavelengths display feature similar functionality f.lux provides night shift feature compatible 64-bit ios devices running ios 9.3 macs 2012 later running macos sierra 10.12.4 feature turned settings ios system preferences macos toggled manually notification center macos control center ios feature enabled disabled siri ios macos feature set enabled sunset turn sunrise default turned custom schedule feature set enable sunset disable sunrise relies user approximate location determine time sunset sunrise user also customize intensity night shift settings ios system preferences macos
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Operating systems
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off-site data protection computing off-site data protection vaulting strategy sending critical data main location main site part disaster recovery plan data usually transported off-site using removable storage media magnetic tape optical storage data also sent electronically via remote backup service known electronic vaulting e-vaulting sending backups off-site ensures systems servers reloaded latest data event disaster accidental error system crash sending backups off-site also ensures copy pertinent data ’ stored on-site although organizations manage store off-site backups many choose backups managed stored third parties specialize commercial protection off-site data storage off-site data also known vaulting backups stored purpose-built vaults generally recognized standards type structure constitutes vault said commercial vaults typically fit three categories hybrid on-site off-site data vaulting sometimes known hybrid online backup involve combination local backup fast backup restore along off-site backup protection local disasters according liran eshel ceo ctera networks ensures recent data available locally event need recovery archived data needed much less often stored cloud hybrid online backup works storing data local disk backup captured high speed either backup software d2d2c disk disk cloud appliance encrypts transmits data service provider recent backups retained locally speed data recovery operations number cloud storage appliances market used backup target including appliances ctera networks nasuni storsimple twinstrata data protection statutes usually non-prescriptive within commercial arena data protected increasingly require active protection data united states federal entities specific requirements defined u.s. national institute standards technology nist nist documentation obtained http //csrc.nist.gov/publications/pubssps.html commercial agencies option using documents compliance requirements statutes mandate protection data
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Computer security
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moti yung mordechai m. moti yung israeli-american cryptographer computer scientist industrial research career yung earned ph.d. columbia university 1988 supervision zvi galil past worked ibm thomas j. watson research center vice president chief scientist certco director advanced authentication research rsa laboratories researcher snap inc. currently research scientist google parallel work industry also held adjunct visiting faculty appointments columbia advised ph.d. students including gödel prize winner matthew k. franklin jonathan katz 1996 adam l. young yung coined term cryptovirology denote use cryptography attack weapon via computer viruses malware contrast traditional protective role particular described first instances ransomware using public-key cryptography young yung introduced notion kleptography show cryptography could used attack host cryptosystems malicious resulting system embedded cryptologic tool resists reverse-engineering detected interacting host cryptosystem attack ransomware also uses internal cryptography attack tool break another cryptographic system snowden affair nist believed mounted first kleptographic attack american federal information processing standard detailing dual ec drbg essentially exploiting repeated discrete logarithm based kleptogram introduced young yung light snowden revelations yung worked detecting correcting cryptosystems subverted implementation work kleptography argument cryptographic systems devices given external body black boxes clipper chip capstone program suggested united states government tried control use cryptography 1990s known first stage crypto wars 1995 yair frankel yung implemented published direct attack clipper chip showing key escrow device tracking authenticating capability namely leaf one device attached messages coming another device message actually decrypted mechanism thus bypassing escrow real time cryptovirology also natural tool crypto wars defined broadly young yung later designed software-only escrow encryption attempt get potential system possessed many desired properties without tamper-proof hardware inherent third party access requirement remains vulnerability nevertheless.. yung made numerous contributions several areas foundations basic cryptographic systems protocols well areas applied cryptography information security also worked theoretical computer science distributed network algorithms yung worked moni naor designing first public key cryptosystems secure chosen-ciphertext attack jonathan katz chosen ciphertext security symmetric encryption schemes via authenticated encryption also worked naor design first secure digital signature schemes based trapdoor functions employing basic primitive universal one-way hash functions signature schemes yung worked early robust multi-party secure schemes via notion shares shares area secure computation protocols 1980s well notion multi secret compact/ batched secret sharing idea also worked rafail ostrovsky basic notion mobile adversary multi-party protocols proactive security fault-tolerance adversaries underlying technique proactive secret sharing yung also worked zero-knowledge proofs commitment schemes particular notion interactive hashing unconditionally hiding commitments general complexity assumptions functional commitment various coauthors yung also worked special goal protocols secure computing e.g set intersection election digital cash auctions threshold cryptosystems fully homomorphic encryption schemes logarithmic depth circuits yung work basic primitives needed communication networks include first efficient password-based authenticated key exchange protocol shown secure without idealized random oracle model assumptions work early 1990 ibm coauthors dealt authentication authenticated key exchange observing cryptographic protocol real networks run concurrently attack suggested iso protocols time led revised modeling problem cryptography zvi galil stuart haber yung predicted mid-1980s large scale networks due scale limitations employ public key technology server public-key certificates interactive protocols idea viewed intellectual predecessor way prevalent version transport layer security implemented mid-1990s using interactive protocols employing ssl certificates servers regarding authentication factors users present systems sign systems traditional factors include knowledge factors ownership factors inherence factors yung coauthors also studied factors available users modern computing environments richer context e.g social relationships area information-theoretic security yung coauthors investigated multicast key pre-distribution system perfectly secure message transmission multi-user authentication codes also coding theory based work includes relating reed–solomon error correction codes cryptographic hardness led interleaving decoding work codes yung coauthored studies methodological framework conducting analyzing side channel attacks also worked early remote attestation software secure run time user running software may try subvert system addition scientific contributions basic applied research yung worked projects industry
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Computer security
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uday ali pabrai uday ali pabrai indian-american entrepreneur based irvine california chairman chief executive officer ecfirst compliance cybersecurity business headquartered waukee iowa pabrai globally renowned cyber security compliance expert featured keynote speaker moderated cybersecurity events international conferences mr. pabrai led numerous cybersecurity engagements worldwide iso 27001 pci dss hitrust nist hipaa/hitech highly sought professional successfully delivered solutions u.s. government agencies firms healthcare systems legal organizations worldwide served interim ciso large health system usa pabrai created several certification programs area information security worked manager security team fermi national accelerator laboratory fermi lab u.s. department energy featured presenter conferences worldwide including fbi infragard hcfa issa isaca isc ² himss hipaa summit comdex microsoft tech forum indiaexpo naseba asis security imprivata healthcare conference healthcare congress pabrai established world first certification program comprehensively addresses global compliance standards regulations area information security certified security compliance specialist cscs also successfully developed leading certification credentials world including ciw 125,000 certificates issued security certified program scp developed certified cyber security architect ccsa program well hitrust cybersecurity strategy workshop previously founded net guru technologies ngt 1994 nasdaq-based firm acquired ngt 1997 launched career 1983 schlumberger leading oilfield services provider dubai associate accountant 1987 started career united states fermi national accelerator laboratory fermilab u.s. department energy facility mr. pabrai presented u.s. defense intelligence agency dia naval surface warfare center mr. pabrai received b.s computer engineering clemson university south carolina received msee degree illinois institute technology iit credentials include security+ ccsfp hitrust cissp issap issmp published hundreds articles regulatory compliance information security published numerous e-security articles leading magazines certification ebusiness advisor computing channel access control security systems covering topics risk management hipaa pki smart cards biometrics e-business disruption ________________
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Computer security
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trust metric psychology sociology trust metric measurement degree one social actor individual group trusts another social actor trust metrics may abstracted manner implemented computers making interest study engineering virtual communities friendster livejournal trust escapes simple measurement meaning subjective universally reliable metrics fact mental process unavailable instruments strong argument use simplistic metrics measure trust due complexity process 'embeddedness trust makes impossible isolate trust related factors generally agreed set properties make particular trust metric better others metric designed serve different purposes e.g provides certain classification scheme trust metrics two groups trust metrics identified trust metrics enable trust modelling reasoning trust closely related reputation systems simple forms binary trust metrics found e.g pgp first commercial forms trust metrics computer software applications like ebay feedback rating slashdot introduced notion karma earned activities perceived promote group effectiveness approach influential later virtual communities empirical metrics capture value trust exploring behavior introspection people determine perceived expressed level trust methods combine theoretical background determining measure defined set questions statistical processing results willingness cooperate well actual cooperation commonly used demonstrate measure trust actual value level trust and/or trustworthiness assessed difference observed hypothetical behaviors i.e would anticipated absence cooperation surveys capture level trust means observations introspection without engaging experiments respondents usually providing answers set questions statements responses e.g structured according likert scale differentiating factors underlying theoretical background contextual relevance one earliest surveys mccroskey scales used determine authoritativeness competence character trustworthiness speakers rempel trust scale rotter scale quite popular determining level interpersonal trust different settings organizational trust inventory oti example exhaustive theory-driven survey used determine level trust within organisation particular research area specific survey developed example interdisciplinary model trust verified using survey uses survey establish relationship design elements web site perceived trustworthiness another empirical method measure trust engage participants experiments treating outcome experiments estimates trust several games game-like scenarios tried estimate trust confidence monetary terms see interesting overview games trust designed way nash equilibrium differ pareto optimum player alone maximize utility altering selfish strategy without cooperation cooperating partners benefit trust therefore estimated basis monetary gain attributable cooperation original 'game trust described abstracted investment game investor broker game played several times randomly chosen players pairs know yielding different results several variants game exist focusing different aspects trust observable behaviour example rules game reversed called game distrust declaratory phase introduced rules presented variety ways altering perception participants interesting games e.g binary-choice trust games gift-exchange game cooperative trust games various forms social games specifically prisoners dilemma popularly used link trust economic utility demonstrate rationality behind reciprocity multi-player games different forms close market simulations exist formal metrics focus facilitating trust modelling specifically large scale models represent trust abstract system e.g social network web trust consequently may provide weaker insight psychology trust particulars empirical data collection formal metrics tend strong foundations algebra probability logic widely recognised way attribute value level trust representation 'trust value claiming certain advantages disadvantages systems assume binary values use fixed scale confidence range -100 +100 excluding zero 0 1 −1 +1 confidence discrete continuous one-dimensional many dimensions metrics use ordered set values without attempting convert particular numerical range e.g see detailed overview also disagreement semantics values disagreement regarding attribution values levels trust specifically visible comes meaning zero negative values example zero may indicate either lack trust distrust lack information deep distrust negative values allowed usually indicate distrust doubt whether distrust simply trust negative sign phenomenon subjective probability focuses trustor self-assessment trust trustee assessment framed anticipation regarding future behaviour trustee expressed terms probability probability subjective specific given trustor assessment situation information available etc situation trustors may different level subjective probability subjective probability creates valuable link formalisation empirical experimentation formally subjective probability benefit available tools probability statistics empirically subjective probability measured one-side bets assuming potential gain fixed amount person bets used estimate subjective probability transaction logic uncertain probabilities subjective logic introduced josang uncertain probabilities called subjective opinions elegant concept combines probability distribution uncertainty opinion trust viewed distribution probability distributions distribution qualified associated uncertainty foundation trust representation opinion evidence confidence trust represented four-tuple trust distrust uncertainty base rate trust distrust uncertainty must add one hence dependent additivity subjective logic example computational trust uncertainty inherently embedded calculation process visible output one e.g possible use similar quadruplet trust distrust unknown ignorance express value confidence long appropriate operations defined despite sophistication subjective opinion representation particular value four-tuple related trust easily derived series binary opinions particular actor event thus providing strong link formal metric empirically observable behaviour finally certaintrust certainlogic share common representation equivalent subjective opinions based three independent parameters named 'average rating 'certainty 'initial expectation hence bijective mapping certaintrust-triplet four-tuple subjective opinions fuzzy systems trust metrics link natural language expressions meaningful numerical analysis application fuzzy logic trust studied context peer peer networks improve peer rating also grid computing demonstrated fuzzy logic allows solve security issues reliable efficient manner set properties satisfied trust metric vary depending application area following list typical properties transitivity highly desired property trust metric situations trusts b b trusts c transitivity concerns extent trusts c. without transitivity trust metrics unlikely used reason trust complex relationships intuition behind transitivity follows everyday experience 'friends friend foaf foundation social networks however attempt attribute exact formal semantics transitivity reveals problems related notion trust scope context example defines conditions limited transitivity trust distinguishing direct trust referral trust similarly shows simple trust transitivity always hold based information advogato model consequently proposed new trust metrics simple holistic approach transitivity characteristic social networks foaf advogato follows everyday intuition assumes trust trustworthiness apply whole person regardless particular trust scope context one trusted friend one also trusted recommend endorse another friend therefore transitivity semantically valid without constraints natural consequence approach thorough approach distinguishes different scopes/contexts trust allow transitivity contexts semantically incompatible inappropriate contextual approach may instance distinguish trust particular competence trust honesty trust ability formulate valid opinion trust ability provide reliable advice sources information contextual approach often used trust-based service composition understanding trust contextual scope foundation collaborative filtering formal trust metric useful define set operations values trust way result operations produce values trust usually least two elementary operators considered exact semantics operators specific metric even within one representation still possibility variety semantic interpretations example representation logic uncertain probabilities trust fusion operations interpreted applying different rules cumulative fusion averaging fusion constraint fusion dempster rule yager modified dempster rule inagaki unified combination rule zhang centre combination rule dubois prade disjunctive consensus rule etc. interpretations leads different results depending assumptions trust fusion particular situatation modelled see detailed discussions growing size networks trust make scalability another desired property meaning computationally feasible calculate metric large networks scalability usually puts two requirements metric attack resistance important non-functional property trust metrics reflects ability overly influenced agents try manipulate trust metric participate bad faith i.e aim abuse presumption trust free software developer resource advogato based novel approach attack-resistant trust metrics raph levien levien observed google pagerank algorithm understood attack resistant trust metric rather similar behind advogato
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Computer security
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shadowsocks shadowsocks free open-source encrypted proxy project widely used mainland china circumvent internet censorship created 2012 chinese programmer named clowwindy multiple implementations protocol made available since typically client software open socks5 proxy machine running internet traffic directed towards similarly ssh tunnel unlike ssh tunnel shadowsocks also proxy udp traffic 22 august 2015 clowwindy announced github thread contacted police could longer maintain project code project subsequently branched removal notice three days later 25 august another proxy application goagent also github repository removed removal projects met media attention news outlets speculating possible connection takedowns ddos targeting github happened several days later danny o'brien electronic frontier foundation published statement matter despite takedown collaborators project continued development project original python implementation still installed pip package manager contents github repository removed server implementations include one go c using event loop library c++ qt gui perl go perl implementations updated regularly may abandoned server implementations listed also support operating client mode also client-only implementations available windows shadowsocks-win macos shadowsocksx-ng android shadowsocks-android ios wingy many clients including shadowsocks-win shadowsocks-android support redirecting system traffic shadowsocks applications explicitly configured allowing shadowsocks used similarly vpn application n't support proxy servers proxifier used redirect application shadowsocks client proxifiers proxycap support shadowsocks directly thus avoiding need shadowsocks client net :shadowsocks name perl implementation shadowsocks protocol client server available cpan shadowsocksr fork original project claimed superior terms security stability upon release found violate general public license source code c client available also criticized solution alleged security issues source project shadowsocks currently development shadowsocksr stopped
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Computer security
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positif project positif project aimed creating framework tools policy-based protection networked systems applications launched february 1 2004 ended january 31 2007 following participants took part project
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Computer security
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swap magic swap magic specialized playstation 2 game disc used tricking console reading non-retail burned game discs homebrew software games outside console region software existed since least mid-2003 several different versions disc developed swap magic related mods magic switch swap tool used allow user swap discs without system aware notable methods modchip due fact void ps2 warranty swap magic disc allows user boot software allows system read discs would normally refuse lack burst cutting area discs burned ordinary dvd drive opposed regular retail discs stamped pressed en masse user removes disc installing small modifications prevent system detecting drive opened replaces another disc started software also allows homebrew software run memory card usb flash drive swap magic non-sony-made playstation 2 bootable discs use method growing splicing stampers original playstation 2 discs method growing stamper original game disc joining new stamper program data essence resulting discs contain portion original disc datel first company outside sony make bootable playstation 2 disc researched protection produced discs protection on-site mastering facility ifpi dvd found inner ring underside data side disc start data mirror part disc hub contain text specified time mastering usually consists string ifpi followed code describing mastering system used followed text product description finally bar code swap magic v1 released compatible v12 slim ps2 swap magic v2 released sony slightly changed design console v13-15 models slim ps2 swap magic v1 work models version 2 widely criticized required user open console therefore voided warranty company responded criticism releasing swap magic v3 require opening console swap magic v3.8 also known coder released adds ability loading action replay cheats booted game however users complained coder compatibility issues well known bugs example games work v3.6 work coder consequently v3.6 remains popular version swap magic
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Computer architecture
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ieee 802.10 ieee 802.10 former standard security functions could used local area networks metropolitan area networks based ieee 802 protocols 802.10 specifies security association management key management well access control data confidentiality data integrity ieee 802.10 standards withdrawn january 2004 working group ieee 802 currently active security wireless networks standardized 802.11i cisco inter-switch link isl protocol supporting vlans ethernet similar lan technologies based ieee 802.10 application 802.10 largely replaced ieee 802.1q standard developed 8 parts parts b e f g h incorporated ieee standard 802.10-1998
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Computer security
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telex anti-censorship system telex research anti-censorship system would allow users circumvent censor without alerting censor act circumvention ready real users proof-of-concept mock system exists telex complements services like tor anonymity network placing telex stations network infrastructure free countries client create tls tunnel indistinguishable allowed traffic way firewalls censored countries neither able detect block access specific parts internet assuming allow access
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Computer security
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google website optimizer google website optimizer free website optimization tool helped online marketers webmasters increase visitor conversion rates overall visitor satisfaction continually testing different combinations website content google website optimizer could test element existed html code page including calls action fonts headlines point action assurances product copy product images product reviews forms allowed webmasters test alternative versions entire page called a/b testing — test multiple combinations page elements headings images body copy known multivariate testing could used multiple stage conversion funnel 1 june 2012 google announced gwo separate product would retired 1 august 2012 functionality would integrated google analytics google analytics content experiments
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Web technology
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socket 754 socket 754 cpu socket originally developed amd supersede athlon xp platform socket 462 also referred socket socket 754 first socket developed amd support new consumer version 64 bit microprocessor family known amd64 socket 754 original socket amd athlon 64 desktop processors due introduction newer socket layouts i.e socket 939 socket 940 socket am2 socket 754 became budget-minded socket use amd athlon 64 sempron processors differs socket 939 several areas although amd promoted socket 754 budget platform desktop encouraged mid- high-end users use newer platforms socket 754 remained time amd high-end solution mobile applications e.g hp zv6000 series however socket s1 released superseded socket 754 mobile cpu segment support dual-core cpus ddr2 sdram first processors using socket 754 came market second half 2003 socket 754 phased favor socket 939 desktops low sales socket remained use laptops replaced s1 2006
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Computer architecture
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multi-master replication multi-master replication method database replication allows data stored group computers updated member group members responsive client data queries multi-master replication system responsible propagating data modifications made member rest group resolving conflicts might arise concurrent changes made different members multi-master replication contrasted master-slave replication single member group designated master given piece data node allowed modify data item members wishing modify data item must first contact master node allowing single master makes easier achieve consistency among members group less flexible multi-master replication multi-master replication also contrasted failover clustering passive slave servers replicating master data order prepare takeover event master stops functioning master server active client interaction primary purposes multi-master replication increased availability faster server response time many directory servers based ldap implement multi-master replication one prevalent multi-master replication implementations directory servers microsoft active directory within active directory objects updated one domain controller replicated domain controllers multi-master replication required domain controllers replicate would cause excessive network traffic large active directory deployments instead domain controllers complex update pattern ensures servers updated timely fashion without excessive replication traffic active directory needs however better served flexible single master operation ca directory supports multi-master replication opends successor product opendj implemented multi-master since version 1.0 opends/opendj multi-master replication asynchronous uses log publish-subscribe mechanism allows scaling large number nodes opends/opendj replication conflict resolution entry attribute level opends/opendj replication used wide area network widely used open source ldap server implements multi-master replication since version 2.4 october 2007 apache couchdb uses simple http-based multi-master replication system built use append data-store use multiversion concurrency control mvcc document contains revision id every record stores evolutionary timeline previous revision ids leading itself—which provides foundation couchdb mvcc system additionally keeps by-sequence index entire database replication process copies last revision document previous revisions source database copied destination database couchdb replicator acts simple http client acting source target database compares current sequence ids database calculates revision differences makes necessary changes target based found history source database bi-directional replication result merely another replication source target values swapped arangodb native multi-model database system using multi-master replication clusters arangodb use cp master/master model single point failure cluster encounters network partition arangodb prefers maintain internal consistency availability clients experience view database regardless node connect cluster continues serve requests even one machine fails cloudant distributed database system uses largely http api apache couchdb exposes ability replicate using multiversion concurrency control mvcc cloudant databases replicate internally nodes within cloudant clusters use multi-master replication stay sync provide high availability api consumers extremedb cluster clustering sub-system mcobject extremedb embedded database product family maintains database consistency across multiple hardware nodes replicating transactions synchronous manner two-phase commit important characteristic extremedb cluster transaction replication contrast log file-based sql statement-based replication schemes may may guarantee success failure entire transactions accordingly extremedb cluster acid compliant system base eventual consistency query executed cluster node return result executed cluster node database clusters implement multi-master replication using one two methods asynchronous multi-master replication commits data changes deferred transaction queue periodically processed databases cluster synchronous multi-master replication uses oracle two phase commit functionality ensure databases cluster consistent dataset microsoft sql provides multi-master replication peer-to-peer replication provides scale-out high-availability solution maintaining copies data across multiple nodes built foundation transactional replication peer-to-peer replication propagates transactionally consistent changes near real-time basic level possible achieve multi-master replication scheme beginning since mysql version 3.23 circular replication departing mariadb mysql ship replication support different nuances terms direct support mariadb natively supports multi-master replication since version 10.0 conflict resolution supported master must contain different databases mysql named multi-source available since version 5.7.6 mysql mysql group replication plugin virtual synchronous multi master conflict handling distributed recovery released 5.7.17 cluster projects mysql cluster supports conflict detection resolution multiple masters since version 6.3 true multi-master capability mysql server also external project galera cluster created codership provides true multi-master capability based fork innodb storage engine custom replication plug-ins replication synchronous conflict possible percona xtradb cluster also combination galera replication library mysql supporting multi master various options synchronous multi-master replication exist postgres-xl available mozilla public license postgresxc known postgres-x2 available license postgresql examples note pgcluster project abandoned 2007 replication documentation postgresql categorises different types replication available various options exist distributed multi-master including bucardo rubyrep bdr bi-directional replication bdr aimed eventual inclusion postgresql core benchmarked demonstrating significantly enhanced performance earlier options bdr includes replication data writes dml well changes data definition ddl global sequences bdr nodes may upgraded online version 0.9 onwards 2ndquadrant developed bdr continuously since 2012 system used production since 2014 latest version bdr 3.6 provides column-level conflict detection crdts eager replication multi-node query consistency many features within ingres replicator objects updated one ingres server replicated servers whether local remote multi-master replication one server fails client connections re-directed another server required ingres servers environment replicate could cause excessive network traffic large implementations instead ingres replicator allows appropriate data replicated appropriate servers without excessive replication traffic means servers environment serve failover candidates servers meet requirements managing subset columns tables departmental solution subset rows geographical region one-way replication reporting server event source target network failure data integrity enforced two-phase commit protocol ensuring either whole transaction replicated none addition ingres replicator operate rdbms ’ multiple vendors connect
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Distributed computing architecture
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double encoding double encoding attack technique used bypass security mechanisms decode data used masquerade directory traversal attack cross-site scripting xss attack double encoding works encoding character want put really decrypts message input illegal characters codice_1 uri encoded becomes codice_2 double uri encoded becomes codice_3 get /download.php file= 252fetc 252fpasswd
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Computer security
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phillip porras phillip a. porras computer scientist security researcher known work combating conficker worm porras leads internet security group sri international computer science laboratory previously manager trusted computer systems department aerospace corporation porras holds 12 u.s. patents named sri fellow 2013 porras attended university california irvine porras author patents involved 2008 case sri international inc. v. internet security systems inc.. conficker worm initial attack porras running honeypot one first security researchers notice part conficker cabal helped combat worm porras team sri published extensive analysis worm 2010 porras co-author blade collaboration sri georgia tech researchers designed prevent drive-by download malware attacks porras named sri fellow 2013 long-term work information security malware analysis recent research openflow
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Computer security
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ballblazer ballblazer 1984 futuristic sports game created lucasfilm games originally released atari 8-bit family ported atari 5200 apple ii zx spectrum amstrad cpc commodore 64 msx later atari 7800 nintendo famicom game called ballblaster development pirated versions game went name well principal creator programmer ballblazer david levine 1990 lucasarts rainbow arts released remake follow-up game called masterblazer game released amiga atari st ms-dos march 31 1997 remake original titled ballblazer champions released sony playstation ballblazer simple one-on-one sports-style game bearing similarities basketball soccer side represented craft called rotofoil controlled either human player computer-controlled droid ten levels difficulty game allows human vs. human human vs. droid droid vs. droid matches basic objective game score points either firing carrying floating ball opponent goal game takes place flat checkerboard playfield player half screen presented first-person perspective player gain possession ball simply running point held force field front craft opponent attempt knock ball away player using fire button player possession ball also fire ball toward goal player possession ball rotofoil automatically turns 90-degree intervals face ball possessing ball turns player toward opponent goal goalposts move side side end playfield goals scored goal becomes narrower pushing ball goal scores one point firing ball posts close range scores two points successfully scoring long range goalposts visible scores three points maximum number total points two players ten meaning points scored would take combined total ten cause opponent score reduced amount resulting kind tug war scoring system game ends either player successfully scores ten points timer runs time runs score tied game goes sudden death first player score wins ballblazer theme music called song grid heard matches algorithmically generated technique designed lucasfilm games team leader peter langston called riffology lead melody assembled predefined set 32 eight-note melody fragments riffs put together randomly algorithm also makes choices several parameters including fast play riff loud play omit elide notes insert rhythmic break melody accompanied bassline drums chords also assembled fly simplified version approach effect music plays forever without repeating without straying far original theme langston experienced jazz rock folk musician said ballblazer music one reviewer eminent jazz player nowiki /nowiki pat metheny said sounded like john coltrane think best compliment far atari 7800 version one rare releases system use pokey additional sound chip sample ballblazer music commodore 64 version computer gaming world stated quick intense ballblazer squeezes atari 400/800 game 've ever seen ... spectacular graphics info rated ballblazer four stars five stating undoubtedly fastest game available 64 recommending gamers strobe-like reflexes zzap 64 gave enthusiastic review commodore 64 version game criticism weak sound effects overall rating 98 game described best sports simulation hit 64 yet
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Computer architecture
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general instrument ay-3-8910 ay-3-8910 3-voice programmable sound generator psg designed general instrument 1978 initially use 16-bit cp1610 one pic1650 series 8-bit microcomputers ay-3-8910 variants used many arcade games—konami gyruss contains five—and pinball machines well sound chip intellivision vectrex video game consoles amstrad cpc oric-1 colour genie elektor tv games computer msx later zx spectrum home computers also used mockingboard cricket sound cards apple ii speech/sound cartridge trs-80 color computer general instrument spinoff microchip technology 1987 chip sold years microchip brand instead also produced license yamaha minor modifications i.e selectable clock divider pin double-resolution double-rate volume envelope table ym2149f atari st uses version produced similar results texas instruments sn76489 market similar period chips longer made functionally-identical clones still active production unofficial vhdl description freely available use fpgas ay-3-8910 essentially state machine state set series sixteen 8-bit registers programmed 8-bit bus used addressing data toggling one external pins instance typical setup cycle would put bus address mode select register switch data mode set contents register bus implemented natively gi cpus recreated glue logic help additional interface adapter mos technology 6522 chip used much common mos technology 6502 zilog z80 cpus six registers controlled pitches produced three primary channels wavelength generate held two eight-bit registers dedicated channel value limited 12-bits reasons total 4095 register value used frequency divider 0 treated 1 different pitches another register controlled period pseudo-random noise generator total 31 different cycle times another controlled mixing noise three primary channels three additional registers controlled volume channels well turning optional envelope controls finally last three registers controlled times envelope controller setting envelope type envelope cycle time total eight envelope types include sawtooth shape triangle shape starting either maximum minimum shape also set repeat cycling effect total 65535 different cycle times set one envelope shared three channels many programmers ignored programmed envelope controllers software controlling volume directly well known trick run hardware envelope cycle times 20hz produce sawtooth pulse-wave like bass sounds although 16 registers four msb bits 8-bit bus must set factory default '0000 value selecting register incorrectly setting msb bits causes chip ignore register change general instruments take orders customized msb bits factory set '0000 chips made customize-set msb register bits allow processor control one ay chip bus e.g mockingboard sound card apple turbosound zx spectrum many new-old-stock nos chips secondary market msb bits factory set non-'0000 value non-0000 value cause significant developmental troubles designers repair technicians software must written identify correct value msb bits given chip also software must changed hardware added allow factory set msb chips used place default '0000 chips ay-3-8910 generates tones base frequencies 125 khz 4 mhz input clock 8 mhz ym2149f well beyond human perception ultrasonic range existence ultrasonic values consequence frequency-divider design order adequate resolution audible frequencies necessary overall clock rate thus output small divisors considerably higher audible range divisors 5 give entirely-ultrasonic output frequencies frequencies equivalent top octave piano keyboard defined reasonable accuracy versus accepted note values even-tempered scale nearly 1 hz precision a440 range even finely lower pitches despite high maximum frequency ability divide figure 4096 means lowest directly definable output frequency 30.6 hz roughly equal b0 third lowest note normal 88-key piano good subsonic everyday speaker systems essence chip able produce decently musical output reasonable pitches found compositions contrast sn76489 10 bits precision frequency dividers base frequency 125 khz theory lack two lowest octaves psg get around sn76489 plays tone generators one octave lower calculated frequency giving one octave less bass one octave less top compared psg 8910 silicon chip sold three different packages ay-3-8910 two general-purpose 8-bit parallel i/o ports b available 40-pin package name ay-3-8912 chip 28-pin package parallel port b simply connected pins smaller packages save cost board space 8912 widely used variant ay-3-8913 chip 24-pin package parallel ports connected users thought small reduction pin count 8912 made less interesting however i/o registers rarely used designers general instruments created fully functional 24 pin alternative released approximately 6 months 8910 8912 chips goal reduce complexity designer reduce foot print pcb yamaha ym2149f 'ssg chip pinout ay-3-8910 minor difference pin 26 could halve master clock pulled low left unconnected would replacing ay-3-8910 chip internal resistor pulls pin high master clock halved yamaha ym3439 cmos version ym2149f available two packages 40-pin dip ym3439-d 44-pin qfp ym3439-f yamaha ymz294 one newest variants ym2149 18-pin package parallel ports one sound output three channels mixed yamaha ymz284 even smaller variation ym2149 16-pin package basically ymz294 without 4/6 mhz selection pin /test pin yamaha ymz285 28-pin package features built-in pcm parallel ports two sound outputs one three ssg channels mixed pcm output toshiba t7766a compatible chip pinout ay-3-8910 used msx models winbond wf19054 jfc 95101 file kc89c72 pinout ay-3-8910 also 100 software compatible 're still production used many slot machines ay-3-8914 pinout 40-pin package ay-3-8910 except control registers chip shuffled around 'expected input a9 pin may different otherwise exactly ay-3-8910 used mattel intellivision ay-3-8930 also known ay8930 enhanced mostly-backwards-compatible version ay-3-8910 function bc2 pin changed ignored assumed 0 regardless pin state otherwise pinout ay-3-8910 variant chip adds number major enhancements separate envelopes three channels opposed one shared envelope variable duty-cycles bits precision note frequency volume envelope frequency much configurable noise generator used covox sound master sound card ibm-pc games took advantage beyond normal ay-3-8910 features chip may produced microchip technology although chip n't designed handle raw pcm data digital sound effect could simulated chip used simple based mixing function combining noise tone three channels could persuaded produce level non-zero wave altering volume level wave could shaped waveform involved cpu usage chips designed purpose mos technology 8364 paula used amiga nevertheless technique widely used platforms atari st less frequently amstrad cpc play sampled music zx spectrum 128 msx play short audio samples games thing fewer times per second order 30 300 per second allows use arbitrary software-defined envelope three channels individually takes negligible cpu power provided timer interrupt vertical blank interrupt used games turn useless envelope functionality set high frequency actually generating waveform usual square wave thanks timbre-altering effects amplitude modulation however obtain harmonic results modulating envelope must related pitch desired note granularity high-frequency envelopes set low music composed chip generally uses technique bass lines another method set one channel output idle high use volume control simple logarithmic 4-bit digital-to-analog converter however resulted poor audio quality 16 output levels logarithmically spaced sophisticated method use three channels wired together exploit non-linearity mixing produce many intermediate output levels modeled non-linearity three channels developers find suitable values exhaustive search done produced 8-bit 3×4-bit lookup table allowed 8-bit audio samples played fairly adequately though well real 8-bit d/a converter problem technique player change volume three channels single operation implies unwanted output levels two successive samples yamaha used ym2149 core produce whole family music chips used mobile phones home computers home arcade video game systems etc example ym2203 also known opn ym2149 plus fm well far advanced successors ym2608 also known opna retained previous features greatly expanded upon ym2612 also known opn2 cut-down ym2608 removed many features including ym2149 sound channels i/o ports ym2610 opnb added features retained ym2149 sound i/o ports
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Computer architecture
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stars virus stars virus computer virus infects computers running microsoft windows named discovered iranian authorities april 2011 iran claimed used tool commit espionage western researchers came believe probably thing duqu virus part stuxnet attack iran stars virus studied laboratory iran – means major vendors antivirus software access samples therefore could assess potential relation duqu stuxnet foreign computer experts say seen evidence virus even doubt actual existence iran claiming stars harmful computer systems said inflict minor damage initial stage might mistaken executable files governmental organizations second attack claimed iran stuxnet computer worm discovered july 2010 targeted industrial software equipment researchers came believe stars virus found iranian computer specialists duqu virus duqu virus keylogger embedded jpeg file since file taken keylogger portion image remained turned image taken hubble telescope showing cluster stars aftermath two galaxies colliding symantec kaspersky crysys researchers came believe duqu stars virus
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Computer security
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core foundation core foundation also called cf c application programming interface api macos ios mix low-level routines wrapper functions apple releases open-source project called cflite used write cross-platform applications macos linux windows third-party open-source implementation called opencflite also exists extends apple distribution building windows linux environments core foundation routines follow certain naming convention deal opaque objects example cfdictionaryref functions whose names begin cfdictionary objects often reference counted manually codice_1 codice_2 internally core foundation forms base types objective-c standard library well prevalent use core foundation passing primitive types data including raw bytes unicode strings numbers calendar dates uuids well collections arrays sets dictionaries numerous macos c routines primarily gui-related operating system level core foundation also provides standardized application preferences management codice_3 bundle handling run loops interprocess communication codice_4 codice_5 basic graphical user interface message dialog codice_6 parts api include utility routines wrappers around existing apis ease use utility routines perform actions file system network i/o codice_7 codice_8 codice_9 endianness translation byte order utilities examples wrapper routines include core foundation wrapper routines unix sockets cfsocket api types core foundation toll-free bridged interchangeable simple cast foundation kit counterparts example one could create codice_10 core foundation type later simply use standard c cast convert objective-c counterpart codice_11 use desired objective-c methods object one normally would core foundation plug-in model cfplugin based microsoft component object model
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Operating systems
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suse linux suse linux computer operating system built top free open source linux kernel distributed system application software open source projects suse linux german origin basically acronym “ software und system-entwicklung ” software systems development mainly developed europe first version appeared early 1994 making suse one oldest existing commercial distributions known yast configuration tool novell bought suse suse brands trademarks 2003 novell one founding members open invention network decided make community important part development process opening widely distribution development outside contributors 2005 creating opensuse distribution opensuse project novell employed 500 developers working suse 2004 27 april 2011 novell suse acquired attachmate group made suse independent business unit later october 2014 entire attachmate group including suse acquired british firm micro focus international suse continues operate independent business unit 2 july 2018 announced micro focus would sell suse blitz 18-679 gmbh subsidiary eqt partners 2.535 billion gesellschaft für software und system entwicklung mbh lit company software system development founded 2 september 1992 nuremberg germany roland dyroff thomas fehr burchard steinbild hubert mantel three founders still mathematics students university fehr already graduated working software engineer original idea company would develop software function advisory unix group according mantel group decided distribute linux offering support name founding s.u.s.e chosen german acronym software und system-entwicklung meaning software systems development full name never used however company known s.u.s.e shortened suse october 1998 2003 capitalized suse official logo current mascot distribution veiled chameleon officially named geeko portmanteau gecko geek following competition company name geeko logo brand evolved time reflect name changes company started service provider among things regularly released software packages included softlanding linux system sls defunct slackware also printed unix/linux manuals offered technical assistance third party products suse initially used characteristics managed suse different fashions building distribution linux s.u.s.e used first slackware 1992 jurix distribution defunct 1996 starting point created florian la roche joined s.u.s.e team began develop yast installer configuration tool would become central point distribution 1996 first distribution name s.u.s.e linux published s.u.s.e linux 4.2 version number caused much discussion version 1.1 using number 4.2 intentional reference answer ultimate question life universe everything hitchhiker guide galaxy science fiction novels english writer douglas adams yast first version number 0.42 similar reference time suse linux incorporated many aspects red hat linux rpm package manager file structure s.u.s.e became largest linux distributor germany 1997 suse llc established direction president managing partner james gray oakland california enabled company develop linux markets americas asia red hat ubiquitous united states suse linux continued grow germany well nordic countries finland sweden october 1998 name changed officially suse without dots linus torvalds creator linux kernel used fairly often suse entered uk 1999 2001 company forced reduce staff significantly order survive 4 november 2003 novell announced would acquire suse linux ag 210 million acquisition finalized january 2004 move reach business audience effectively suse introduced suse linux enterprise server 2001 months novell purchase changed company name suse linux suse name acronym according j. philips novell corporate technology strategist asia pacific region novell would medium term alter way suse developed novell annual brainshare conference 2004 first time computers run suse linux announced proprietary suse administration program yast2 would released gpl license 4 august 2005 novell announced suse professional series would become open launch opensuse project community software always open source opensuse opened development process allowing developers users test develop previously development work accomplished in-house suse version 10.0 first version offered public beta testing suse linux 10.0 included open source proprietary applications retail boxed-set editions part change yast online update server access became free suse linux users also first time gnome desktop upgraded equal status traditional kde november 2005 suse founder hubert mantel announced resignation company stated novell acquisition changed suse beyond expectations believe company founded 13 years earlier resignation apparently stemmed dispute implementation ximian products gnome-based default desktop environment linux distribution re-joined year later 3 november 2006 renewed 25 july 2011 novell signed agreement microsoft covering improvement suse ability interoperate microsoft windows cross-promotion/marketing products patent cross-licensing agreement considered controversial free software community 22 november 2010 novell announced agreed acquisition attachmate group 2.2 billion attachmate group plans operate novell two units suse becoming stand-alone business anticipates change relationship suse business opensuse project result transaction u.s. department justice announced order proceed first phase acquisition certain patents patent applications novell inc. cptn holdings llc owners would alter original agreements address department antitrust concerns department said originally proposed deal would jeopardize ability open source software linux continue innovate compete development distribution server desktop mobile operating systems well middleware virtualization products stipulations regarding licensing patents acquisition completed 27 april 2011 subsequently 23 july 2011 attachmate group launched new website suse business 20 november 2014 attachmate group merged micro focus form micro focus group suse operated separate business unit dedicated product portfolio 2 july 2018 announced micro focus would sell suse business segment eqt partners 2.535 billion suse provides thirteen-year product life cycle suse linux enterprise 11 12 detailed eol eos eoxs end-of-extended-support information see suse linux available two brands opensuse suse linux enterprise opensuse free community distribution driven opensuse project includes latest bleeding edge linux technologies designed home users enthusiasts suse linux enterprise suse tested certified open-source solution major enterprises opensuse freely available community project releases versions comparatively frequent basis generally uses latest versions various open source projects includes suse linux enterprise suse commercial edition suse releases much less frequently enabling offer support effectively enterprise production deployments certified wide variety enterprise applications offers number special enterprise features including high availability point sale extensions suse historically uses heavily-tested subset packages opensuse linux basis suse linux enterprise suse offers suse linux enterprise server suse linux enterprise desktop focuses packages fit specific purpose example suse linux enterprise desktop include apache web server suse linux enterprise server include xgl/compiz contrast opensuse separate distributions server desktop tablets rather repositories contain needed software use installation patterns accomplish opensuse driven opensuse project community sponsored suse develop maintain suse linux components equivalent historic suse linux professional acquisition suse linux novell suse decided make community central development process theoretical development cycle 8 months lifetime duration critical updates 18 months date release fully freely available immediate download opensuse sixth popular linux distribution 2013 fourth popular 2014 according distrowatch suse develops multiple products enterprise business line business products target corporate environments higher life cycle 10 years extendable 13 longer development cycle 6 18 months guarantee stability potential expense development speed technical support certification independent hardware software vendors suse linux enterprise products available sale updates fees suse linux enterprise fewer packages opensuse distribution differences desktop applications suited consumers business enterprise products installed using linux kernel novell open enterprise server oes uses suse linux enterprise server platform product also known oes-linux suse linux enterprise included vmware vsphere licensing june 25 2014 'free noted suse partners website suse suse studio product web interface built using ruby rails opensuse kiwi open build service tools allowed users put together custom linux distribution graphically generate output including large variety virtual machine disk images suse studio merged open build service resulting project renamed suse studio express september 2017
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Operating systems
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nat traversal network address translator traversal computer networking technique establishing maintaining internet protocol connections across gateways implement network address translation nat nat traversal techniques required many network applications peer-to-peer file sharing voice ip nat devices allow use private ip addresses private networks behind routers single public ip address facing internet internal network devices communicate hosts external network changing source address outgoing requests nat device relaying replies back originating device leaves internal network ill-suited hosting servers nat device automatic method determining internal host incoming packets destined problem general web access email however applications peer-to-peer file sharing voip services video game consoles require clients servers well incoming requests easily correlated proper internal host furthermore many types services carry ip address port number information application data potentially requiring substitution deep packet inspection network address translation technologies standardized result methods used nat traversal often proprietary poorly documented many traversal techniques require assistance servers outside masqueraded network methods use server establishing connection others based relaying data increases bandwidth requirements latency detrimental real-time voice video communications nat traversal techniques usually bypass enterprise security policies enterprise security experts prefer techniques explicitly cooperate nat firewalls allowing nat traversal still enabling marshalling nat enforce enterprise security policies ietf standards based security model realm-specific ip rsip middlebox communications midcom following nat traversal techniques available recent proliferation symmetric nats reduced nat traversal success rates many practical situations mobile public wifi connections hole punching techniques stun ice fail traversing symmetric nats without help relay server practiced turn techniques traverse symmetric nats attempting predict next port opened nat device discovered 2003 yutaka takeda panasonic communications research laboratory 2008 researchers waseda university port prediction techniques effective nat devices use known deterministic algorithms port selection predictable yet non-static port allocation scheme uncommon large scale nats used 4g lte networks therefore port prediction largely ineffective mobile broadband networks ipsec virtual private network clients use nat traversal order encapsulating security payload packets traverse nat ipsec uses several protocols operation must enabled traverse firewalls network address translators many routers provide explicit features often called ipsec passthrough windows xp nat traversal enabled default windows xp service pack 2 disabled default case vpn server also behind nat device rare controversial security issue ipsec nat-t patches also available windows 2000 windows nt windows 98 nat traversal ipsec may used enable opportunistic encryption traffic systems nat traversal allows systems behind nats request establish secure connections demand hosted nat traversal hnt set mechanisms including media relaying latching used intermediaries ietf advises using latching internet recommends ice security reasons
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Computer security
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retroarch retroarch free open-source cross-platform front-end emulators game engines video games media players applications reference implementation libretro api designed fast lightweight portable without dependencies licensed gnu gplv3 retroarch runs programs converted dynamic libraries called libretro cores using several user interfaces command-line interface graphical user interfaces gui optimized gamepads famous one called xmb clone sony xmb several input audio video drivers plus sophisticated features like dynamic rate control audio filters multi-pass shaders netplay gameplay rewinding cheats etc retroarch ported many platforms run several pc operating systems windows macos linux home consoles playstation 3 xbox 360 wii u etc handheld consoles playstation vita nintendo 3ds etc smartphones android ios etc embedded systems raspberry pi odroid etc even web browsers using emscripten compiler formerly known ssnes initially based pseudonymous programmer byuu libretro predecessor libsnes began development 2010 hans-kristian themaister arntzen committing first change github intended replacement bsnes qt-based interface grew support emulation cores april 21 2012 ssnes officially renamed retroarch reflect change direction retroarch version 1.0.0.0 released january 11 2014 time available 7 distinct platforms february 16 2016 retroarch became one first ever applications implement support vulkan graphics api done day api official release day november 27 2016 libretro team announced alongside lakka libreelec-based retroarch operating system retroarch would patreon crowdfunding platform allow providing bounties developers fix specific software bugs cover costs matchmaking servers december 2016 gogames – company contracted video game developer publisher sega – approached retroarch developers intention using software sega forever project ultimately cooperation come fruition due licensing disagreements april 2018 input lag compensation added libretro team plans release retroarch onto steam free download integrating steamworks features platform july 2019 first major dedicated emulation title released platform major features include retroarch run libretro core retroarch available many platforms availability specific core varies per platform non-exhaustive table systems available retroarch project core based retroarch praised number systems games play single interface criticized difficult configure due extensive number options available user time praised advanced features possesses android praised fact overlays customized expandability libretro cores supports compatibility several usb bluetooth controller peripherals addition app free ads tyler loch writing ars technica said retroarch 'input lag compensation mode arguably biggest improvement experience retro gaming community yet seen
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Computer architecture
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duplicity software duplicity software suite provides encrypted digitally signed versioned remote backup files requiring little remote server released terms gnu general public license gpl duplicity free software duplicity devises scheme first archive complete full backup subsequent incremental backups add differences latest full incremental backup chains consisting full backup series incremental backups recovered point time incremental steps taken incremental backups missing incremental backups following reconstructed using gnupg librsync tar rdiff transmit data backup repository use ssh/scp/sftp local file access rsync ftp amazon s3 google cloud storage rackspace cloud files others duplicity works best unix-like operating systems linux bsd mac os x though used windows cygwin currently duplicity supports deleted files full unix permissions directories symbolic links fifos device files hard links
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Computer security
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google file system google file system gfs googlefs proprietary distributed file system developed google provide efficient reliable access data using large clusters commodity hardware last version google file system codenamed colossus released 2010 gfs enhanced google core data storage usage needs primarily search engine generate enormous amounts data must retained google file system grew earlier google effort bigfiles developed larry page sergey brin early days google still located stanford files divided fixed-size chunks 64 megabytes similar clusters sectors regular file systems extremely rarely overwritten shrunk files usually appended read also designed optimized run google computing clusters dense nodes consist cheap commodity computers means precautions must taken high failure rate individual nodes subsequent data loss design decisions select high data throughputs even comes cost latency gfs cluster consists multiple nodes nodes divided two types one master node large number chunkservers file divided fixed-size chunks chunkservers store chunks chunk assigned globally unique 64-bit label master node time creation logical mappings files constituent chunks maintained chunk replicated several times throughout network default replicated three times configurable files high demand may higher replication factor files application client uses strict storage optimizations may replicated less three times order cope quick garbage cleaning policies master server usually store actual chunks rather metadata associated chunks tables mapping 64-bit labels chunk locations files make mapping files chunks locations copies chunks processes reading writing particular chunk taking snapshot chunk pursuant replicate usually instigation master server due node failures number copies chunk fallen beneath set number metadata kept current master server periodically receiving updates chunk server heart-beat messages permissions modifications handled system time-limited expiring leases master server grants permission process finite period time process granted permission master server modify chunk modifying chunkserver always primary chunk holder propagates changes chunkservers backup copies changes saved chunkservers acknowledge thus guaranteeing completion atomicity operation programs access chunks first querying master server locations desired chunks chunks operated i.e outstanding leases exist master replies locations program contacts receives data chunkserver directly similar kazaa supernodes unlike file systems gfs implemented kernel operating system instead provided userspace library google file system implement posix api files organized hierarchically directories identified pathnames file operations create delete open close read write supported supports record append allows multiple clients append data file concurrently atomicity guaranteed deciding benchmarking results used relatively small number servers 15 file system achieves reading performance comparable single disk 80–100 mb/s reduced write performance 30 mb/s relatively slow 5 mb/s appending data existing files authors present results random seek time master node directly involved data reading data passed chunk server directly reading client read rate increases significantly number chunk servers achieving 583 mb/s 342 nodes aggregating large number servers also allows big capacity somewhat reduced storing data three independent locations provide redundancy
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Computer file systems
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vulnerability assessment computing vulnerability assessment process defining identifying classifying security holes information technology systems attacker exploit vulnerability violate security system known vulnerabilities authentication vulnerability authorization vulnerability input validation vulnerability deploying system first must go series vulnerability assessments ensure build system secure known security risks new vulnerability discovered system administrator perform assessment discover modules vulnerable start patch process fixes place another assessment run verify vulnerabilities actually resolved cycle assess patch re-assess become standard method many organizations manage security issues primary purpose assessment find vulnerabilities system assessment report conveys stakeholders system secured vulnerabilities intruder gained access network consisting vulnerable web servers safe assume gained access systems well assessment report security administrator able determine intrusion occurred identify compromised assets take appropriate security measures prevent critical damage system depending system vulnerability assessment many types level host assessment looks system-level vulnerabilities insecure file permissions application level bugs backdoor trojan horse installations requires specialized tools operating system software packages used addition administrative access system tested host assessment often costly term time thus used assessment critical systems tools like cops tiger popular host assessment network assessment one assess network known vulnerabilities locates systems network determines network services use analyzes services potential vulnerabilities process require configuration changes systems assessed unlike host assessment network assessment requires little computational cost effort vulnerability assessment penetration testing two different testing methods differentiated basis certain specific parameters
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Computer security
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magic magic third party multitasking-capable tos-compatible operating system atari st range computers including newer clone machines also variants run part magicmac magicpc emulation environments kernel magic largely written hand-coded motorola 68000 assembly language offers magic originally released mag x 1992 time tos featured limited multitasking form desk accessory programs simple programs accessed desk menu multitasked using cooperative task switching contrast magic offered preemptive multitasking giving ability run multiple well-behaved gem applications well non-graphical software name changed mag x magic release version 3.0 added many improvements significant amount mint compatibility version 4.0 added support atari falcon finally 1995 version 5.0 brought significant addition loadable file system support along implementation vfat long file names number improvements gemdos layer including threads signals latest atari version 6.2 atari slow improve hardware systems apparent mid late 1990s apple mac superior hardware platform given two shared similar user interface mac logical upgrade many atari users 1995 variant magic known magicmac released allowing atari users run well-behaved software much newer mac hardware later versions magicmac offered improved integration mac os allowed well-behaved atari software access native graphics modes offered host machine addition emulations standard atari screen modes release mac os x original versions magicmac would longer run operated low level within mac os order function 2001 new version magicmac magicmacx released use mac os x updated 2004 recently september 2009 universal binary running natively powerpc intel macs summer 1996 another version released magicpc time allowing atari users run software top microsoft windows magic versions 6.0 6.2 released use clone machines manufactured medusa computer systems late 1990s include significant enhancements support fat32 increased mint compatibility support newer processors hardware found clone systems magic implementation gem desktop greatly enhanced version included original tos systems initially named magxdesk changing magicdesk release magic 3.0 offered features missing original desktop including unlike gem desktop magicdesk built magic instead could launched application startup possible start magic shell popular alternatives including jinnee thing
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Operating systems
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slot 1 slot 1 refers physical electrical specification connector used intel microprocessors including pentium pro celeron pentium ii pentium iii single dual processor configurations implemented intel switched back traditional socket interface socket 370 1999 introduction pentium ii cpu need greater access testing made transition socket slot necessary previously pentium pro intel combined processor cache dies socket 8 package connected full-speed bus resulting significant performance benefits unfortunately method required two components bonded together early production process testing possible result single tiny flaw either die made necessary discard entire assembly causing low production yield high cost intel subsequently designed circuit board cpu cache remained closely integrated mounted printed circuit board called single-edged contact cartridge secc cpu cache could tested separately final assembly package reducing cost making cpu attractive markets high-end servers cards could also easily plugged slot 1 thereby eliminating chance pins typical cpu bent broken installing socket form factor used slot 1 5-inch-long 242-contact edge connector named sc242 prevent cartridge inserted wrong way slot keyed allow installation one direction sc242 later used amd slot well two slots identical mechanically electrically incompatible discourage slot users trying install slot 1 cpu connector rotated 180 degrees slot motherboards new slot 1 intel added support symmetric multiprocessing smp maximum two pentium ii pentium iii cpus used dual slot motherboard celeron official smp support also converter cards known slotkets hold socket 8 pentium pro cpu used slot 1 motherboards specific converters however rare another kind slotket allows using socket 370 cpu slot 1 many latter devices equipped voltage regulator modules order supply new cpu lower core voltage motherboard would otherwise allow single edge contact cartridge secc used beginning slot 1-era pentium ii cpus inside cartridge cpu enclosed hybrid plastic metal case back housing plastic several markings name pentium ii intel logo hologram model number front consists black anodized aluminum plate used hold cpu cooler secc form solid cpu resting safely inside case compared socket-based cpus pins bent cpu less likely damaged improper installation cooler following secc sepp-form single edge processor package appeared market designed lower-priced celeron cpus form lacks case entirely consisting solely printed-circuit board holding components form factor called secc2 used late pentium ii pentium iii cpus slot 1 created accommodate switch flip chip packaging front plate carried coolers mounted straight pcb exposed cpu die incompatible secc cartridges historically three platforms intel p6-cpus socket 8 slot 1 socket 370 slot 1 successor socket 8 socket 8 cpus pentium pro directly l2-cache embedded cpu located outside core circuit board shared core exception later slot 1 cpus coppermine core l2-cache embedded die beginning 2000 pentium-iii-cpus fc-pga-housing appeared slot 1 slowly succeeded socket 370 intel already offered socket 370 slot 1 time since beginning 1999 socket 370 initially made low-cost celeron processors slot 1 thought platform expensive pentium ii early pentium iii models cache core embedded die slot 1 also obsoleted old socket 7 least regarding intel standard platform home-user superseding intel p5 pentium mmx cpu intel completely left socket 7 market
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Computer architecture
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calf studio gear calf studio gear often referred calf plugins set open source lv2 plugins linux platform suite intends complete set plugins audio mixing virtual instruments mastering version 0.90.0 47 plugins suite calf studio gear development started late 2007 lv2 plugin standard infancy calf studio gear one first projects bring graphical audio plugins linux first versions 0.0.19 included support ladspa dssi well dropped december 2011 project initiated krzysztof foltman 2009 markus schmidt became interested development plugin suite due frustration proprietary software driving force behind plugins ever since responsible overall design calf studio gear well brains behind dsp many plugins calf studio gear complete suite plugins linux included plugins past calf plugins known cause crashes within ardour digital audio workstation primarily due use fftw library recently thread safe since october 2014 calf studio gear moved away using fftw library released version 0.0.60 may 2015
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Operating systems
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cloudberry backup cloudberry backup online backup software developed cloudberry lab software integrated 3rd-party cloud storage providers supports data backup restore windows desktop servers macos linux additionally offers support microsoft sql server microsoft exchange vmware hyper-v office 365 g suite google apps cloudberry backup available several licensed editions well free offering cloudberry backup desktop free licensed versions cloudberry managed backup saas solution designed help manage backup recovery across multiple computers servers cloudberry backup designed automate backup recovery files folders system images storage-agnostic meaning storage decoupled backup license customers work directly cloud storage providers pricing features need cloudberry backup supports 20 cloud storage providers including amazon s3 amazon glacier microsoft azure google cloud platform backblaze b2 wasabi openstack s3 compatible others cloudberry backup supports multiple data storage tiers including lower cost options like microsoft azure cool blob storage archive blob storage amazon s3 infrequent access glacier google cloud storage nearline coldline 2011 cloudberry backup released support amazon s3 subsequently updated support microsoft azure google cloud platform number cloud vendors late 2011 cloudberry lab released windows server edition followed support microsoft sql server microsoft exchange bare metal restore cloudberry backup added additional operating system support linux macos 2015 freeware version cloudberry backup also appeared year cloudberry backup written primarily c c++ programming languages windows versions also rely .net cloudberry managed backup built using c asp.net angular node.js cloudberry backup provides backup recovery functionality cloud local storage network shares backup recovery plans configured using graphical user interface command-line interface also available editions cloudberry backup supported operating systems windows macos linux cloudberry lab developed proprietary block-level algorithm speeds data uploads backups cloud addition company uses proprietary image-based algorithm back complete systems image files retaining ability recover specific files within images desired cloudberry backup supports recovery images directly cloud-based virtual server services amazon ec2 azure virtual machines google compute engine well bare-metal devices product restore system images computers operating system installed using bootable usb iso disk images cloudberry backup software supports synthetic full backup functionality amazon s3 wasabi hot storage performing typical incremental backup sequence advised perform full backups time time time resource consuming reduce bandwidth amount data uploaded synthetic full backup feature software scans data previously backed storage uploads new modified blocks instead full set files according cloudberry lab tests synthetic full backups 80 percent faster typical full image-based backup cloudberry backup perform backups microsoft sql server microsoft exchange databases recover active running state linux cloudberry backup allows users back files folders cloud storage product supports variety linux distributions including ubuntu debian suse red hat fedora centos oracle linux amazon linux cloudberry backup configured perform complete backup file directory disk image also supports incremental backup functionality block level meaning users able back new updated portions files initial backup completed backups executed manually via custom schedules cloudberry backup supports file compression 256-bit aes encryption server-side encryption encryption-at-rest cloud storage support filename encryption also available cloudberry backup provides flexible data recovery options backups restored physical virtual cloud virtual machines product restore files backup recover selected individual files product includes recovery wizard guides users data restoration process cloudberry lab features also include cloudberry backup available several editions designed address different use cases windows desktop edition intended file image-based backups whereas windows server microsoft exchange microsoft sql server ultimate editions designed meet needs businesses running windows server macos linux editions address backup needs platforms pricing cloudberry lab products based one-time purchase fee purchasers pay one-time fee computer server devices want operate cloudberry lab pricing per device per user license purchased device limit number users accounts operate product device long use product free versions cloudberry backup available personal use well cloudberry managed backup saas solution designed managed service providers msps businesses need way centrally manage backup customers within environments hosted saas solution provides means manage monitor large environments single dashboard cloudberry managed backup uses subscription-based licensing model supports white-labeling rebranded managed service providers sell backup service brand cloudberry managed backup integrated autotask connectwise optitune office 365 google g suite ninjarmm cloudberry backup received several awards including latest silver stevie award 2018 product constantly ranked one market leaders g2 crowd updates rankings every three months cloudberry lab developer cloudberry backup gold winner smb product year category best biz awards 2018 international addition awards cloudberry lab holds partnerships certifications microsoft vmware google cloud connectwise oracle openstack amazon web services
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Computer security
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kerrighed kerrighed open source single-system image ssi cluster software project project started october 1998 paris research group french national institute research computer science control 2006 2011 project mainly developed kerlabs january 2012 linux clustering mission kerlabs adopted new company cluster inc. headquartered pacific grove california january 18 2012 kerrighed 3.0 ported ubuntu 12.04 linux kernel v3.2 kerrighed implemented extension linux operating system helps scientific applications numerical simulations use power applications may using openmp message passing interface and/or posix multithreaded programming model kerrighed implements set global resource management services aim making resource distribution transparent applications managing resource sharing applications taking benefit whole cluster resources demanding applications kerrighed provides development framework allowing easily implement dynamic scheduling policies without kernel modification kerrighed provides several features distributed shared memory sequential consistency model processes migration one cluster node another limited extent checkpointing kerrighed introduces container concept entity abstraction files memory kerrighed node starts 'root container local resources available access resources globally one must start kerrighed container one node add nodes kerrighed container
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Distributed computing architecture
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daniel robbins computer programmer daniel robbins computer programmer consultant best known founder former chief architect gentoo linux project 2008 launched funtoo project free linux distribution based gentoo became project lead hacker organizer also currently works time albuquerque new mexico 'open source/community strategy lead zenoss president funtoo technologies time system administrator university new mexico albuquerque robbins formed distribution enoch linux later renamed gentoo 2002 however like many free software projects gentoo struggled create business model would support key developers robbins resigned chief architect 26 april 2004 citing considerable personal debt desire spend time family formed gentoo foundation transferred gentoo intellectual property gentoo run full community-based model rejoin project short time august 2006 becoming developer february 2007 joining amd64 team resigned early march 2007 several high-profile criticisms way gentoo run since robbins left ... since resignation gentoo founder benevolent dictator project 2004 newly established gentoo foundation battling lack clear directions frequent developer conflicts ... mid-july 2007 emerged robbins still technically legal president gentoo foundation ... would like see fun gentoo lot less politics apparent role president gentoo foundation may opportunity change things better need look ... 2008 robbins began work funtoo project created allow work extending technologies originally created gentoo robbins move microsoft may 2005 attracted attention within linux community historically combative relationship microsoft described role working bill hilf ... helping microsoft understand open source community-based projects ... however robbins resigned less year later 16 january 2006 due frustrations unable fully utilize technical skills position later 2006 joined fsmlabs socorro new mexico work rtlinux daniel robbins also president funtoo technologies consulting firm founded 2006 located albuquerque new mexico
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Operating systems
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leaf driver leaf driver refers device driver accesses logically physically existent devices i/o bus implements functions defined device transferring data device accessing device registers leaf devices requiring leaf drivers typical peripheral devices disks tapes network adapters framebuffer forth drivers devices export traditional character block driver interfaces use user processes read write data storage communication devices see also nexus driver
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Operating systems
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shar unix operating system shar abbreviation shell archive archive format created unix shar utility shar file type self-extracting archive valid shell script executing recreate files extract files standard unix bourne shell sh usually required note shar command specified single unix specification formally component unix legacy utility shar format advantage plain text poses risk due executable reason older general tar file format usually preferred even transferring text files gnu provides version shar gnu sharutils collection unshar programs written operating systems always reliable shar files shell scripts theoretically anything shell script including using incompatible features enhanced workalike shells limiting utility outside unix world drawback self-extracting shell scripts kind shar rely particular implementation programs shell archives created older versions makeself example original unreal tournament linux installer fails run bash 3.x due change missing arguments codice_1 built-in command handled james gosling generally credited writing first version shar utility also wrote early example concept form simple shell script version concept vms operating system written 1987 michael bednarek melbourne institute applied economic social research dcl script vms_shar.com later maintained extended james gray xerox andy harper king college london
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Computer file systems
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convergence ssl convergence proposed strategy replacing ssl certificate authorities first put forth moxie marlinspike august 2011 giving talk titled ssl future authenticity black hat security conference demonstrated firefox addon server-side notary daemon talk marlinspike proposed current problems certificate authority ca system could reduced single missing property called trust agility convergence aimed provide strategy claimed agile secure distributed 2013 marlinspike focused ietf proposal called tack designed uncontroversial first step advocates dynamic certificate pinning instead full ca replacement reduces number times third party needs trusted development convergence continued convergence extra fork 2014 convergence based previous work perspectives project carnegie mellon university like perspectives convergence authenticated connections contacting external notaries unlike perspectives convergence notaries could use number different strategies beyond network perspective order reach verdict purpose certificate authority conventional ssl system vouch identity site checking ssl certificate without vouchsafing one open man-in-the-middle attack single site vouched single certificate authority ca ca trusted user web browsers typically include list default trusted certificate authorities display warning untrusted connection site vouchsafed trusted ca problem system user browser vendor loses trust ca removing ca browser list trusted authorities means losing trust sites used ca happened major browsers lost trust diginotar ca sites registered ca get new certificate authorities see certificate authority ca compromise examples trust breaches convergence however level redundancy single point failure several notaries could vouch single site user could choose trust several notaries would vouch sites notaries disagreed whether site identity correct user could choose go majority vote err side caution demand notaries agree content single notary voting method controlled setting browser addon user chose distrust certain notary non-malicious site could still trusted long remaining trusted notaries trusted thus longer single point failure september 2011 qualys announced would run two notary servers june 2016 servers appeared list notaries maintained convergence wiki
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Computer security
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milk race video game milk race computer game released 1987 zx spectrum commodore 64 atari 8-bit family msx amstrad cpc developed phil berry stuart ruecroft composer david whittaker icon design based around internationally acclaimed event world cycle race milk race known tour britain simulator designed coincide 1987 event starting newcastle upon tyne north england midlands london finishing line basic premise game control bike using acceleration braking choosing correct gear conserve energy
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Computer architecture
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mirai malware mirai malware turns networked devices running linux remotely controlled bots used part botnet large-scale network attacks primarily targets online consumer devices ip cameras home routers mirai botnet first found august 2016 malwaremustdie whitehat malware research group used largest disruptive distributed denial service ddos attacks including attack 20 september 2016 computer security journalist brian krebs web site attack french web host ovh october 2016 dyn cyberattack according chat log anna-senpai robert coelho mirai named 2011 tv anime series mirai nikki source code mirai published hack forums open-source since source code published techniques adapted malware projects devices infected mirai continuously scan internet ip address internet things iot devices mirai includes table ip address ranges infect including private networks addresses allocated united states postal service department defense mirai identifies vulnerable iot devices using table 60 common factory default usernames passwords logs infect mirai malware infected devices continue function normally except occasional sluggishness increased use bandwidth device remains infected rebooted may involve simply turning device short wait turning back reboot unless login password changed immediately device reinfected within minutes upon infection mirai identify competing malware remove memory block remote administration ports victim iot devices identified “ first entering rapid scanning phase ① asynchronously “ statelessly ” sent tcp syn probes pseudo-random ipv4 addresses excluding hard-coded ip blacklist telnet tcp ports 23 2323 ” iot device responds probe attack enters brute-force login phase phase attacker tries establish telnet connection using predetermined username password pairs list credentials logins default usernames passwords iot vendor iot device allows telnet access victim ip along successfully used credential sent collection server hundreds thousands iot devices use default settings making vulnerable infection infected device monitor command control server indicates target attack reason use large number iot devices bypass anti-dos software monitors ip address incoming requests filters sets block identifies abnormal traffic pattern example many requests come particular ip address reasons include able marshall bandwidth perpetrator assemble alone avoid traced mirai internet things iot devices threat stopped arrest actors since actors utilizing mirai malware source code openly shared github use evolve mirai new variants expand botnet node networking previously untouched iot devices detail recent progress variants listed following paragraphs 12 december 2017 researchers identified variant mirai exploiting zero-day flaw huawei hg532 routers accelerate mirai botnets infection implementing two known soap related exploits routers web interface cve-2014–8361 cve-2017–17215 mirai version called satori 14 january 2018 new variant mirai dubbed “ okiru ” already targeting popular embedded processor like arm mips x86 powerpc others found targeting arc processors based linux devices first time argonaut risc core processor shorted arc processors second-most-popular embedded 32 bit processor shipped 1.5 billion products per year including desktop computers servers radio cameras mobile utility meters televisions flash drives automotive networking devices smart hubs tv modems routers wifi internet things noted however relatively small number arc-based devices run linux therefore exposed mirai 18 january 2018 successor mirai reported designed hijack cryptocurrency mining operations 26 january 2018 two similar mirai variant botnets reported modified version weaponizes edb 38722 d-link router exploit enlist vulnerable iot devices vulnerability router home network administration protocol hnap utilized craft malicious query exploited routers bypass authentication cause arbitrary remote code execution less modified version mirai called masuta japanese transliteration master modified version called puremasuta march 2018 new variant mirai dubbed omg emerged surface added configurations target vulnerable iot devices turning proxy servers new firewall rules allow traffic travel generated http socks ports added configurations mirai code ports open traffic omg sets 3proxy – open-source software available russian website may june 2018 another variant mirai dubbed wicked emerged added configurations target least three additional exploits including affecting netgear routers cctv-dvrs wicked scans ports 8080 8443 80 81 attempts locate vulnerable unpatched iot devices running ports researchers suspect author created wicked sora owari omni botnets early july 2018 reported least thirteen versions mirai malware detected actively infecting linux internet things iot internet three designed target specific vulnerabilities using exploit proof concept without launching brute-forcing attack default credential authentication month published report infection campaign mirai malware android devices android debug bridge tcp/5555 actually optional feature android operating system discovered feature appears enabled android phones end 2018 mirai variant dubbed miori started spread remote code execution vulnerability thinkphp framework affecting versions 5.0.23 5.1.31 vulnerability continuously abused evolved mirai variants dubbed hakai yowai january 2019 variant speakup february 2019 mirai used alongside bashlite ddos attack 20 september 2016 krebs security site reached 620 gbit/s ars technica also reported 1 tbit/s attack french web host ovh 21 october 2016 multiple major ddos attacks dns services dns service provider dyn occurred using mirai malware installed large number iot devices many still using default usernames passwords attacks resulted inaccessibility several high-profile websites including github twitter reddit netflix airbnb many others attribution dyn attack mirai botnet originally reported level 3 communications mirai later revealed used ddos attacks rutgers university 2014 2016 left faculty students campus unable access outside internet several days time additionally failure university central authentication service caused course registration services unavailable critical times academic semester university reportedly spent 300,000 consultation increased cyber-security budget university 1 million response attacks university cited attacks among reasons increase tuition fees 2015-2016 school year person alias exfocus claimed responsibility attacks stating reddit ama /r/rutgers subreddit user student school ddos attacks motivated frustrations university bus system user later claimed interview new jersey-based blogger lied affiliated university attacks funded anonymous client security researcher brian krebs later alleged user indeed student rutgers university latter interview given attempt distract investigators staff deep learning security observed steady growth mirai botnets 21 october attack mirai also used attack liberia internet infrastructure november 2016 according computer security expert kevin beaumont attack appears originated actor also attacked dyn security affairs website taken offline hour twenty minutes published article mirai okiru 14 january 2018 end november 2016 approximately 900,000 routers deutsche telekom produced arcadyan crashed due failed tr-064 exploitation attempts variant mirai resulted internet connectivity problems users devices talktalk later patched routers new variant mirai discovered talktalk routers british man suspected behind attack arrested luton airport according bbc january 17 2017 computer security journalist brian krebs posted article blog krebs security disclosed name person believed written malware krebs stated likely real-life identity anna-senpai named anna nishikinomiya character shimoneta author mirai actually paras jha owner ddos mitigation service company protraf solutions student rutgers university update original article paras jha responded krebs denied written mirai fbi reported questioned jha involvement october 2016 dyn cyberattack december 13 2017 paras jha josiah white dalton norman entered guilty plea crimes related mirai botnet daniel kaye 29 also known alias bestbuy popopret spiderman accused using infected network computers known mirai botnet attack blackmail lloyds banking group barclays banks according nca extradited germany uk according report kaye also pleaded guilty court hijacking 900,000 routers network deutsche telekom researchers pointing handle name nexus zeta responsible author new variants mirai dubbed okiru satori masuta puremasuta august 21 2018 grand jury indicted kenneth currin schuchman 20 aka nexus zeta knowingly causing transmission program information code commands result conduct intentionally caused damage without authorization protected computers according indictment filed u.s. district court anchorage followed arrest trial suspect american electronic musician composer james ferraro 2018 album four pieces mirai references mirai ongoing narrative
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Computer security
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perplexity information theory perplexity measurement well probability distribution probability model predicts sample may used compare probability models low perplexity indicates probability distribution good predicting sample perplexity discrete probability distribution p defined h p entropy bits distribution x ranges events base need 2 perplexity independent base provided entropy exponentiation use base measure also known domains order-1 true diversity perplexity random variable x may defined perplexity distribution possible values x special case p models fair k -sided die uniform distribution k discrete events perplexity k random variable perplexity k uncertainty fair k -sided die one said k -ways perplexed value random variable unless fair k -sided die k values possible overall uncertainty greater values probability greater 1/ k decreasing overall value summing perplexity sometimes used measure hard prediction problem always accurate two choices one probability 0.9 chances correct guess 90 percent using optimal strategy perplexity 2= 1.38 inverse perplexity case fair k-sided die represents probability guessing correctly 1/1.38 0.72 0.9 perplexity exponentiation entropy clearcut quantity entropy measure expected average number bits required encode outcome random variable using theoretical optimal variable-length code cf equivalently regarded expected information gain learning outcome random variable information measured bits model unknown probability distribution p may proposed based training sample drawn p given proposed probability model q one may evaluate q asking well predicts separate test sample x x ... x also drawn p perplexity model q defined formula_3 customarily 2 better models q unknown distribution p tend assign higher probabilities q x test events thus lower perplexity less surprised test sample exponent may regarded average number bits needed represent test event x one uses optimal code based q low-perplexity models better job compressing test sample requiring bits per test element average q x tends high exponent may also regarded cross-entropy formula_5 denotes empirical distribution test sample i.e. formula_6 x appeared n times test sample size n natural language processing perplexity way evaluating language models language model probability distribution entire sentences texts using definition perplexity probability model one might find example average sentence x test sample could coded 190 bits i.e. test sentences average log-probability -190 would give enormous model perplexity 2 per sentence however common normalize sentence length consider number bits per word thus test sample sentences comprised total 1,000 words could coded using total 7.95 bits per word one could report model perplexity 2 247 per word words model confused test data choose uniformly independently among 247 possibilities word lowest perplexity published brown corpus 1 million words american english varying topics genres 1992 indeed 247 per word corresponding cross-entropy log247 7.95 bits per word 1.75 bits per letter using trigram model often possible achieve lower perplexity specialized corpora predictable simply guessing next word brown corpus word accuracy 7 percent 1/247 0.4 percent naive use perplexity measure predictiveness might lead one believe guess based unigram statistics brown corpus trigram statistics yielded word perplexity 247 using trigram statistics would improve chances correct guess
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Computational linguistics
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variadic computer science operator function variadic take varying number arguments arity fixed specific articles see
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Programming language topics
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thermal attack thermal attack aka thermal imaging attack approach exploits heat traces uncover entered credentials attacks rely phenomenon heat transfer one object another authentication heat transfers users hands surface interacting leaving heat traces behind analyzed using thermal cameras operate far-infrared spectrum traces recovered used reconstruct passwords cases attack successful even 30 seconds user authenticated thermal attacks performed victim authenticated alleviating need in-situ observation attacks e.g. shoulder surfing attacks affected hand occlusions smudge attacks reveal order entries graphical passwords android lock patterns thermal attacks reveal order entries even case pins alphanumeric passwords reason thermal attacks leak information order entry keys buttons user touches first lose heat time recently touched ones maintain heat signature longer time results distinguishable heat patterns tell attacker entry entered first thermal attacks shown effective plastic keypads ones used enter credit card pins supermarkets restaurants handheld mobile devices smartphones tablets paper published conference human factors computing systems chi 2017 abdelrahman et al showed attack feasible today smartphones also proposed ways mitigate attack swiping randomly screen distort heat traces forcing maximum cpu usage seconds
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Computer security
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arabic ontology arabic ontology linguistic ontology arabic language used arabic wordnet ontologically-clean content people use also tree i.e classification concepts/meanings arabic terms formal representation concepts arabic terms convey content ontologically well-founded benchmarked scientific advances rigorous knowledge sources rather speakers ’ naïve beliefs wordnets typically ontology tree explored online ontology structure i.e. data model similar wordnet structure concept ontology given unique concept identifier uri informally described gloss lexicalized one synonymous lemma terms term-concept pair called sense given senseid set senses called synset concepts senses described attributes era area specify used lexicalization type example sentence example instances ontological analysis others semantic relations e.g. subtypeof partof others defined concepts important individuals included ontology individual countries seas individuals given separate individualids linked concepts instanceof relation concepts arabic ontology mapped synsets wordnet well bfo dolce terms used arabic ontology mapped lemmas ldc sama database arabic ontology seen next generation wordnet ontologically-clean arabic wordnet follows structure i.e. data model wordnet fully mapped wordnet however critical foundational differences arabic ontology used many application domains urls arabic ontology designed according w3c best practices publishing linked data described following url schemes allows one also explore whole database like exploring graph
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Computational linguistics
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skype protocol skype protocol proprietary internet telephony network used skype protocol specifications made publicly available skype official applications using protocol closed-source skype network interoperable voice ip voip networks without proper licensing skype numerous attempts study and/or reverse engineer protocol undertaken reveal protocol investigate security allow unofficial clients june 20 2014 microsoft announced deprecation old skype protocol within several months date order continue using skype services skype users update skype applications released 2014 users able log older skype versions clients announcement made whether smarttv hardware phones built-in skype functionality continue work without interruptions new skype protocol—microsoft notification protocol 24—promised better offline messaging better messages synchronization across skype devices deprecation became effective second week august 2014 skype first peer-to-peer ip telephony network network contains three types entities supernodes ordinary nodes login server client maintains host cache ip address port numbers reachable supernodes skype user directory decentralized distributed among supernodes network supernodes grouped slots 9–10 supernodes slots grouped blocks 8 slots previously client good bandwidth restrictions due firewall network address translation nat adequate processing power could become supernode placed extra burden connected internet without nat skype used computers internet connections third parties udp hole punching directly connect two clients behind nat completely relay users calls 2012 microsoft altered design network brought supernodes control hosted servers data centres microsoft time defended move saying believe approach immediate performance scalability availability benefits hundreds millions users make skype community time concern regarding privacy implications change appear proven true revelation prism surveillance program june 2013 skype support use ipv6 protocol would greatly reduce complexity associated aforementioned ipv4 communication structure supernodes relay communications behalf two clients behind firewalls one-to-many network address translation without relaying supernodes two clients firewall nat difficulties would unable make receive calls one another skype tries get two ends negotiate connection details directly sometimes sum problems ends prevent direct conversation established problems firewalls nat signaling encrypted using rc4 however method obfuscates traffic key recovered packet voice data encrypted aes skype client application programming interface api opens network software developers skype api allows programs use skype network get white pages information manage calls skype code closed source protocol standardized parts client use internet direct indy open source socket communication library july 8 2012 researcher benin ouanilo medegan released articles proof concept code results reverse engineering skype client many networking security companies claim detect control skype protocol enterprise carrier applications specific detection methods used companies often proprietary pearson chi-squared test stochastic characterization naive bayes classifiers two approaches published 2007 rc4 encryption algorithm used obfuscate payload datagrams xor two 32-bit values transformed 80-byte rc4 key using unknown key engine notable misuse rc4 skype found tcp streams udp unaffected first 14 bytes 10 known user since consist hash username password xor-ed rc4 stream cipher reinitialized encrypt rest tcp stream tcp packets skype init tcp packet contains almost traffic ciphered command parameters appended object list object list compressed object number string ip port even another object list object id id identifies command parameter object packets compressed algorithm variation arithmetic compression uses reals instead bits reverse engineering skype protocol inspecting/disassembling binaries prohibited terms conditions skype license agreement however european union law allows reverse-engineering computer program without getting permission author inter-operability purposes united states digital millennium copyright act provides protections reverse engineering software purposes interoperability software also legal precedents united states reverse-engineering aimed interoperability file formats protocols addition countries specifically permit program copied purposes reverse engineering
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Internet protocols
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micro transport protocol micro transport protocol µtp sometimes also utp open udp-based variant bittorrent peer-to-peer file sharing protocol intended mitigate poor latency congestion control problems found conventional bittorrent tcp providing reliable ordered delivery devised automatically slow rate packets data transmitted users peer-to-peer file sharing torrents interferes applications example protocol automatically allow sharing adsl line bittorrent application web browser µtp emerged research internet2 qos high-performance bulk transport adapted use background transport protocol plicto founded stanislav shalunov later acquired bittorrent inc. 2006 developed within new owner first introduced µtorrent 1.8.x beta branches publicized alpha builds µtorrent 1.9 implementation µtp used µtorrent later separated libutp library published mit license first free software client implement µtp ktorrent 4.0. libtorrent implements µtp since version 0.16.0 used qbittorrent since 2.8.0 tixati implements µtp since version 1.72 vuze formerly azureus implements µtp since version 4.6.0.0 transmission implements µtp since version 2.30 congestion control algorithm used µtp known low extra delay background transport ledbat aims decrease latency caused applications using protocol maximizing bandwidth latency excessive additionally information µtp congestion controller used choose transfer rate tcp connections ledbat described rfc 6817 2009 details µtp implementation different then-current internet draft µtp also adds support nat traversal using udp hole punching two port-restricted peers third unrestricted peer acts stun server
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Internet protocols
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doppelganger domain doppelganger domain domain spelled identical legitimate fully qualified domain name fqdn missing dot host/subdomain domain used malicious purposes typosquatting traditional attack vector web distribute malware harvest credentials vectors email remote access services ssh rdp vpn also leveraged whitepaper godai group doppelganger domains demonstrated numerous emails harvested without anyone noticing someone email address someone finance.somecompany.example doppelganger domain would financesomecompany.example hence someone trying send email user forget dot finance someone financesomecompany.example would go doppelganger domain instead legitimate user
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Web technology
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backslash linux backslash linux ubuntu debian-based operating system developed india kumar priyansh amd64 intel x64-based personal computers based free software every release operating system named characters 2013 disney film frozen since third major release backslash linux olaf backslash linux used custom version kde called backslash shell default user desktop backslash linux design hybrid resembles macos first glance kde bottom instead kde-based distribution ships many gnome-based applications moreover buttons title bar resemble macos arranged windows-like manner top bar resembles gnome first glance app opened displays universal menu bar looking similar macos unity development backslash linux started mid 2016 ubuntu-based compatible repositories ad packages uses discover software center handle installation/removal software user interface aims intuitive new users without consuming many resources backslash linux based ubuntu long term support releases developer actively maintains bugs security years even development continues next release three pre-release versions codenamed alpha beta gamma released first stable release still available download may 2017 taken website first stable version backslash linux backslash linux anna published 2 november 2016 based ubuntu 14.04 ran linux kernel 4.2 ran cinnamon desktop environment extra plugins plank dock provide new look support download option version still available backslash linux website article also published linux.com introducing backslash linux backslash linux anna complete system providing end-users types needed daily use software notable applications included font viewer pdf reader simple scan deluge bittorrent client dropbox google chrome google earth pidgin im skype wps office vlc media player clementine screen reader gdebi package manager wine pre-installed order support windows based applications games second release backslash linux published 20 december 2016 called backslash linux elsa elsa built atop ubuntu long-term support release — ubuntu 16.04 ran flagship desktop environment elementary os pantheon lot applications used backslash linux anna dropped release cut iso size also added lot additional applications besides core applications shipped elementary os replaced epiphany browser google chrome many additional utilities like skype wine deluge bittorrent client dictionary also shipped out-of-the-box inclusion gnome boxes virtualisation desktops another time-saver backslash linux elsa embarked inclusion many utilities like backups dvd burner teamviewer synaptic package manager pidgin im replaced empathy im also included firewall full libreoffice suite addition modem manager noticed helpful managing external modem cards albert present search companion backslash elsa easily activated using meta+space shortcut key tweaking desktop changing themes colors cursors also present desktop present pantheon default also introduced active desktop right-click options pantheon desktop backslash linux olaf third major current release backslash linux published 9 may 2017 introduced 150+ new features last versions backslash linux based ubuntu 16.04 ran backslash shell customised kde desktop due heavily modified beautiful desktop gained much attention received much praise earlier versions version backslash linux removed applications cut iso size also brought many refinements google chrome replaced open-source chromium wine upgraded version 2.0.1 applications like skype firewall modem manager dvd burner dropbox empathy im gnome boxes teamviewer deluge dictionary present earlier version backslash linux dropped version albert search companion replaced krunner search libreoffice lost position wps office back backslash linux series release olaf thunderbird also included version better email experience simple idea include best apps available instead kde-specific apps reason see gnome apps like calendar disks maps release backslash linux olaf also introduced full-screen applauncher resembled launchpad macos fork discontinued application slingshot reviewing backslash linux olaf souris procambodian said think best build distro feels complete ’ need much time config cause ’ everything working box backslash linux kristoff released public beta 13 august 2017 adding features like fingerprint hwe kernel support linux distro world followed deepin linux also added fingerprint support deepin 15.5 released 30 november 2017 stable release backslash linux kristoff made christmas december 25 2017 builds upon previous release backslash linux olaf fixing almost bugs also introduces backslash shell v2.0 performance improvements highly worked also introduces new app called multiview system optimizer installer issues fixed ui redesigned gtk+ support greatly worked backslash linux kristoff also supports fingerprint recognition lockscreen terminal authentication app authentications multitouch gesture support also implemented addition wine redshift night light also introduced better temperature controls additional components include sidebar better notification audio network management hardware-enabled hwe kernel includes support snaps new login screen video background also cover flow task switcher also includes desktop cube animation switching multiple virtual desktops applications included geary apache openoffice gparted dolphin file manager modem manager synaptic package manager vlc media player others security backslash based ubuntu security software updates provided canonical ltd. default programs run standard user privileges administrator privileges given whenever required increased security sudo tool used assign temporary privileges performing administrative tasks allows root account remain locked helps prevent inexperienced users inadvertently making catastrophic system changes opening security holes network ports closed default prevent hacking built-in firewall allows end-users install network servers control access gui available configure backslash compiles packages using gnu compiler collection features position-independent code buffer overflow protection hardening computing software backslash supports full disk encryption well encryption home private directories backslash linux installation simple fully graphical backslash linux booted run usb flash drive pc capable booting usb drive option saving settings flash drive ubuntu live usb creator program available install ubuntu-based distribution usb drive windows program unetbootin allows backslash linux usb burning installation supports logical volume manager lvm automatic partitioning disk encryption utf-8 default character encoding supports variety non-roman type script unicode backslash linux also released two official flavours mate gnome also server edition operating system soon development support versions flavous server edition discontinued development focused mainstream release
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Operating systems
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idms ca idms integrated database management system primarily network model codasyl database management system mainframes first developed b.f. goodrich later marketed cullinane database systems renamed cullinet 1983 since 1989 product owned computer associates ca technologies renamed advantage ca-idms later simply ca idms roots idms go back pioneering database management system called integrated data store ids developed general electric team led charles bachman first released 1964 early 1960s ids taken original form computer group b.f. goodrich chemical division re-written language called intermediate system language isl isl designed portable system programming language able produce code variety target machines since isl actually written isl able ported machine architectures relative ease produce code would execute chemical division computer group given thought selling copies idms companies told management software products business eventually deal struck john cullinane buy rights market product cullinane required remit royalties back b.f. goodrich add-on products listed billed separate products even mandatory core idms product work sometimes confused customers original platforms ge 235 computer ge datanet-30 message switching computer later product ported ibm mainframes dec icl hardware ibm-ported version runs ibm mainframe systems system/360 system/370 system/390 zseries system z9 mid-1980s claimed 2,500 idms licenses sold users included strategic air command ford canada ford europe jaguar cars clarks shoes uk axa/ppp mapfre royal insurance tesco manulife hudson bay company cleveland clinic bank canada general electric aetna bt uk version use decsystem series computers sold dec marketed dbms10 later dbms20 1976 source code licensed icl ported software run 2900 series mainframes subsequently also older 1900 range icl continued development software independently cullinane selling original ported product name icl 2900 idms enhanced version idmsx form used many large uk users example pay-as-you-earn system operated inland revenue many idmsx systems uk government still running 2013 early mid-1980s relational database management systems started become popular encouraged increasing hardware power move minicomputers client–server architecture relational databases offered improved development productivity codasyl systems traditional objections based poor performance slowly diminishing cullinet attempted continue competing ibm db2 relational databases developing relational front-end range productivity tools included automatic system facility asf made use pre-existing idms feature called lrf logical record facility asf fill-in-the-blanks database generator would also develop mini-application maintain tables difficult judge whether features may successful extending selling life product made little impact long term users stayed idms primarily interested high performance relational capabilities widely recognized helped high-profile campaign e. f. codd father relational model significant difference relational database network database relational veneer 1989 computer associates continued cullinet acquisition development released release 12.0 full sql 1992-93 nowadays ca technologies actively markets supports ca idms enhanced idms subsequent releases tcp/ip support two-phase commit support xml publishing ziip specialty processor support web-enabled access combination ca idms server sql option gui database administration via ca idms visual dba tool ca-idms systems today still running businesses worldwide many customers opted web-enable applications via ca-idms sql option part ca technologies dual database strategy one sophisticated features idms built-in integrated data dictionary idd idd primarily developed maintain database definitions idms database dbas database administrators users interfaced idd using language called data dictionary definition language dddl idd also used store definitions code products idms family ads/online idms-dc idd power extensible could used create definitions anything companies used develop in-house documentation data model offered users codasyl network model main structuring concepts model records sets records essentially follow cobol pattern consisting fields different types allows complex internal structure repeating items repeating groups distinctive structuring concept codasyl model set confused mathematical set codasyl set represents one-to-many relationship records one owner many members fact record member many different sets key factor distinguishes network model earlier hierarchical model records set belongs named set type different set types model different logical relationships sets fact ordered sequence records set used convey information record participate owner member number sets records identity identity represented value known database key idms codasyl implementations database key directly related physical address record disk database keys also used pointers implement sets form linked lists trees close correspondence logical model physical implementation strictly necessary part codasyl model characteristic successful implementations responsible efficiency database retrieval also makes operations database loading restructuring rather expensive records accessed directly database key following set relationships direct access using key values initially direct access hashing mechanism known codasyl model calc access idms calc access implemented internal set linking records share hash value owner record occupies first bytes every disk page subsequent years versions idms added ability access records using btree-like indexes idms organizes databases series files files mapped pre-formatted so-called areas areas subdivided pages correspond physical blocks disk database records stored within blocks dba allocates fixed number pages file area dba defines records stored area details stored idms intersperses special space-allocation pages throughout database pages used keep track free space available page database reduce i/o requirements free space tracked pages free space area falls 30 four methods available storing records idms database direct sequential calc via fujitsu/icl idmsx version extends two methods page direct random direct mode target database key specified user stored close possible db key actual db key record stored returned application program sequential placement confused indexed sequential simply places new record end area option rarely used calc uses hashing algorithm decide place record hash key provides efficient retrieval record entire calc area preformatted header consisting special calc owner record hashing algorithm determines page number physical disk address determined record stored page near possible linked header record page using calc set calc records linked page calc owner record using single link-list pointers calc owner located page header thus owns set records target particular page whether records stored page case overflow another page calc provides extremely efficient storage retrieval idms retrieve calc record 1.1 i/o operations however method cope well changes value primary key expensive reorganization needed number pages needs expanded work-around expand area run application program scans area sequentially calc record uses modify verb update record results calc record connected calc set correct target page calculated area new page range downside method vanishingly calc records target pages navigating page calc set likely involve many io operations result recommended use work-around extreme circumstances performance suffer via placement attempts store record near owner particular set usually records clustered physical page owner leads efficient navigation record accessed following set relationship via allows records stored different idms area stored separately owner yet remain clustered together efficiency within idmsx may also offset owner set number pages page direct idmsx similar direct mode however target database page number specified record connected calc chain page random idmsx allocates target page number record occurrence stored using calc algorithm either uses key within record case un-keyed random uses date time storage seed calc algorithm sets generally maintained linked lists using database key pointer every record includes forward link next record database designer choose whether include owner pointers prior pointers provided navigation directions slower versions idms subsequently included ability define indexes either record indexes allowing records located knowledge secondary key set indexes allowing members set retrieved key value idmsx page direct random placement records typically used conjunction record indexes described indexes subject placement rules either direct really means calc using index id key calc idms many non-profit user associations across globe composed information technology professionals use and/or support ca idms related products include
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Databases
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jonas öberg jonas öberg born 22 november 1977 norrköping sweden free open-source software activist describing instigator world free worked free software foundation europe gnu project fscons creative commons shuttleworth foundation started develop software 1991 installed first gnu/linux operating system 1993 eventually joined webmaster gnu project late 1990s spent time mit ai labs met richard stallman others free software foundation joining bazaar conference new york since 2002 award committee free software foundation free software awards 2001 founding member free software foundation europe took role vice president 22 november 2001 former vice president loïc dachary took step back focus gnu savannah worked creative commons several years including running course fundraising peer peer university became first regional coordinator europe 2011 work organisation eventually led position fellow shuttleworth foundation work focus creating tools prototypes embedding metadata licensing attribution requirements digital works company commons machinery featured one 12 winners tech stars 2014 competition european commission neelie kroes digital agenda 19th-century wooden house north sweden continuously renovating lives outside stockholm gnesta sweden married julia velkova media researcher member internet society bulgaria marriage took place ice hotel sweden 8 march 2013
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Operating systems
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acer pica m6100 pica system logic chipset designed acer laboratories introduced 1993 pica stands performance-enhanced input-output cpu architecture based jazz architecture developed microsoft supported mips technologies r4000 r4400 microprocessors chipset designed computers run windows nt therefore used arc firmware boot windows nt chipset consisted six chips cpu secondary cache controller buffer i/o cache bus controller memory controller two data buffers pica used acer formula 4000 personal workstation nec sold oem name riscstation image
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Computer architecture
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rackspace rackspace inc. american managed cloud computing company based windcrest texas suburb san antonio company also offices australia united kingdom switzerland netherlands germany singapore mexico hong kong rackspace data centers operating texas chicago kansas city virginia united kingdom germany australia hong kong company rackspace email division operates blacksburg va offices located austin texas 2016 rackspace closed san francisco office rackspace became public 2008 2016 purchased taken private apollo global management llc 1996 richard yoo started small internet service provider called cymitar network systems garage apartment san antonio texas company began application development work addition offering basic internet access web hosting 1997 yoo brought dirk elmendorf company began develop internet applications primary business company re-formed cymitar technology group cymitar technology group grew patrick condon recruited california joined team 1998 coincidentally three company founders students one time trinity university san antonio although founders began application developers end users found companies either know want host applications founders wanted focus application development–not hosting–but unable find opportunity outsource hosting work eventually founders realized would better create product serve hosting need launch company rackspace launched october 1998 richard yoo ceo although hosting companies focused technology end hosting rackspace created fanatical support offering focus service support march 28 2000 rackspace received funding lead investor norwest venture partners sequoia capital george j still jr. managing partner norwest subsequently joined board directors 2008 rackspace moved headquarters building occupied datapoint corporation then-unoccupied windsor park mall windcrest texas rackspace chairman graham weston owned montgomery ward building mall 2006 sold developer city windcrest purchased south mall create residential retail complex facility located next roosevelt high school many roosevelt students intern rackspace fortune top 100 best companies work 2008 placed rackspace first year rackspace applied consideration company praised transparency regular open book meetings held top level leaders share in-depth financial information employees 2011 2013 company named one top 100 places work fortune august 8 2008 rackspace opened trading new york stock exchange ticker symbol rax initial public offering ipo raised 187.5 million initial public offering included 15,000,000 shares common stock price 12.50 per share ipo well public market lost 20 initial price almost immediately around 3:45pm cst december 18 2009 rackspace experienced outage customers using dallas–fort worth data center – including rackspace cloud september 8 2010 rackspace received national attention decided discontinue providing web hosting service one customers dove world outreach center reaction dove world pastor terry jones plan burn several copies qur'an anniversary september 11th attacks rackspace claims violated company policy move came criticism notably terry jones described indirect attack freedom speech others questioned appropriateness rackspace action stating absolutely reason web hosts editorial policy gives jones attention makes look persecuted june 3 2011 rackspace intervened application queensland host rack servers trademark business name australia may 26 2013 author bill schley book 'the unstoppables inspired culture rackspace became new york times bestseller may 15 2014 rackspace hired morgan stanley evaluate strategic options including selling merging technology companies october 2014 rackspace announced would sell support google work apps business customers august 2016 confirmed apollo global management reached agreement buy company 4.3 billion sale completed november 2016 rackspace officially ended trading new york stock exchange november 3 2016 may 2017 ceo taylor rhodes announced leaving company may 16 work smaller private company different city may 2017 rackspace named joe eazor new ceo april 2019 company named kevin jones new ceo october 22 2008 rackspace announced purchasing cloud storage provider jungle disk vps provider slicehost february 16 2012 rackspace acquired sharepoint911 microsoft sharepoint consulting company based cincinnati ohio may 25 2017 rackspace announced agreement acquire tricore solutions september 11 2017 rackspace announced plans acquire datapipe september 17 2018 rackspace announced acquired relationedge acquisitions include cloudkick anso labs mailgun objectrocket exceptional cloud services zerovm rackspace launched serverbeach san antonio january 2003 lower-cost alternative dedicated servers designed technology hobbyists want flexibility reliability richard yoo catalyst startup serverbeach bandwidth colocation provider peer 1 hosting known cogeco peer 1 purchased serverbeach october 2004 7.5 million peer 1 hosting entered uk managed hosting market january 2009 serverbeach brand competes directly uk arm rackspace run dominic monkhouse former managing director rackspace limited october 2006 mosso inc. launched experimented white-labeling hosting services eventually division became foundation rackspace cloud computing offering october 1 2007 rackspace acquired webmail.us private e-mail hosting firm located blacksburg va originally branded mailtrust may 20 2009 became part newly formed cloud office division rackspace october 22 2008 rackspace acquired slicehost provider virtual servers jungle disk provider online backup software services rackspace announced march 8 2017 plans expansion portfolio include managed service google cloud platform program began beta testing july 18 2017 planned full offering late 2017 rackspace partnered google customer reliability engineering group google site reliability engineers ensure cloud applications run speed reliability google widely-used products 2010 rackspace contributed source code cloud files product openstack project apache license become openstack object storage component april 2012 rackspace announced would implement openstack compute underlying technology cloud servers product change introduced new control panel well add-on cloud services offering databases server monitoring block storage virtual networking 2015 two rackspace executives elected board openstack foundation february 2016 interview cto john engates stated rackspace use openstack power public private cloud
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Distributed computing architecture
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remote direct memory access computing remote direct memory access rdma direct memory access memory one computer another without involving either one operating system permits high-throughput low-latency networking especially useful massively parallel computer clusters rdma supports zero-copy networking enabling network adapter transfer data wire directly application memory application memory directly wire eliminating need copy data application memory data buffers operating system transfers require work done cpus caches context switches transfers continue parallel system operations reduces latency message transfer however strategy presents several problems related fact target node notified completion request single-sided communications 2018 rdma achieved broader acceptance result implementation enhancements enable good performance ordinary networking infrastructure example roce rdma converged ethernet able run either lossy lossless infrastructure addition iwarp enables ethernet rdma implementation physical layer using tcp/ip transport combining performance latency advantages rdma low-cost standards-based solution rdma consortium dat collaborative played key roles development rdma protocols apis consideration standards groups internet engineering task force interconnect software consortium hardware vendors started working higher-capacity rdma-based network adapters rates 100 gbit/s reported software vendors red hat oracle corporation support apis latest products engineers started developing network adapters implement rdma ethernet red hat enterprise linux red hat enterprise mrg support rdma microsoft supports rdma windows server 2012 via smb direct vmware esxi product also supports rdma 2015 common rdma implementations include virtual interface architecture rdma converged ethernet roce infiniband omni-path iwarp
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Operating systems
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entity framework entity framework ef open source object-relational mapping orm framework ado.net part .net framework since entity framework version 6 separated .net framework entity framework set technologies ado.net support development data-oriented software applications architects developers data-oriented applications typically struggled need achieve two different objectives must model entities relationships logic business problems solving must also work data engines used store retrieve data data may span multiple storage systems protocols even applications work single storage system must balance requirements storage system requirements writing efficient maintainable application code entity framework enables developers work data form domain-specific objects properties customers customer addresses without concern underlying database tables columns data stored entity framework developers work higher level abstraction deal data create maintain data-oriented applications less code traditional applications first version entity framework efv1 included .net framework 3.5 service pack 1 visual studio 2008 service pack 1 released 11 august 2008 version widely criticized even attracting 'vote confidence signed approximately one thousand developers second version entity framework named entity framework 4.0 efv4 released part .net 4.0 12 april 2010 addressed many criticisms made version 1 third version entity framework version 4.1 released april 12 2011 code first support refresh version 4.1 named entity framework 4.1 update 1 released july 25 2011 includes bug fixes new supported types version 4.3.1 released february 29 2012 updates like support migration version 5.0.0 released august 11 2012 targeted .net framework 4.5 also version available .net framework 4 without runtime advantages version 4 version 6.0 released october 17 2013 open source project licensed apache license v2 like asp.net mvc source code hosted github using git version number improvements code-first support microsoft decided modernize componentize bring .net cross-platform linux osx elsewhere meaning next version entity framework would complete rewrite 27 june 2016 released entity framework core 1.0 alongside asp.net core 1.0 .net core 1.0 originally named entity framework 7 renamed highlight complete rewrite rather incremental upgrade n't replace ef6 ef core 1.0 licensed apache license v2 built entirely open github ef core 1.0 shares conceptual similarities prior versions entity framework completely new codebase designed efficient powerful flexible extensible run windows linux osx support new range relational nosql data stores ef core 2.0 released 14 august 2017 along visual studio 2017 15.3 asp.net core 2.0 architecture ado.net entity framework bottom consists following entity data model edm specifies conceptual model csdl data using modelling technique called entity data model extended version entity-relationship model data model primarily describes entities associations participate edm schema expressed schema definition language sdl application xml extended markup language addition mapping msl elements conceptual schema csdl storage schema ssdl must also specified mapping specification also expressed xml visual studio also provides entity designer visual creation edm mapping specification output tool xml file *.edmx specifying schema mapping edmx file contains ef metadata artifacts csdl/msl/ssdl content three files csdl msl ssdl also created edited hand entity data model wizard visual studio initially generates one-to-one 1:1 mapping database schema conceptual schema cases relational schema elements composed tables primary foreign keys gluing related tables together contrast entity types define conceptual schema data entity types aggregation multiple typed fields – field maps certain column database – contain information multiple physical tables entity types related independent relationships physical schema related entities also exposed similarly – via field whose name denotes relation participating accessing instead retrieving value column database traverses relationship returns entity collection entities related entity types form class objects entities conform entities instances entity types entities represent individual objects form part problem solved application indexed key example converting physical schema described two entity types logical schema mapping physical schema represented entity data model edm specified xml file ado.net entity framework uses edm actually perform mapping letting application work entities internally abstracting use ado.net constructs like dataset recordset ado.net entity framework performs joins necessary entity reference information multiple tables relationship traversed entity updated traces back table information came issues sql update statements update tables data updated ado.net entity framework uses esql derivative sql perform queries set-theoretic operations updates entities relationships queries esql required translated native sql flavor underlying database entity types entity sets form logical edm schema exposed anything ado.net entity framework includes object service presents entities objects elements relationships exposed properties thus entity objects front-end instances edm entity types lets object oriented languages access use similarly front-ends created expose entities via web services e.g. wcf data services xml used entities serialized persistence storage over-the-wire transfer entities** instances entitytype represent individual instances objects customer orders information pertains identity entity defined entity type instance sense entity type defines class entity belongs also defines properties entity properties describe aspect entity giving name type properties entity type ado.net entity framework fully typed fully compatible type system used dbms system well common type system .net framework property simpletype complextype multi-valued well entitytype belong namespace entitykey property uniquely identifies instance entity type different property types distinguished follows entity instances housed entitycontainers per-project containers entities project one named entitycontainers reference entities across multiple namespaces entity types multiple instances one entity type stored collections called entitysets one entity type multiple entitysets edm primitive types simple types two entity types related either association relation containment relation example shipment billed customer association whereas order contains order details containment relation containment relation also used model inheritance entities relation two entity types specified relationship type instances called relationships relate entity instances future releases kinds relationship types composition identification may introduced relationship types characterized degree arity count entity types relate multiplicity however initial release ado.net entity framework relationships limited binary degree two bi-directional relationship multiplicity defines many entity instances related together based multiplicity relationships either one-to-one one-to-many many-to-many relationships entities named name called role defines purpose relationship relationship type also operation action associated allows action performed entity event action performed related entity relationship specified take action operation done related entity example deleting entity forms part relation ondelete operation actions taken association relationships different semantics either ends different actions specified either end ado.net entity framework uses xml based data definition language called schema definition language sdl define edm schema sdl defines simpletypes similar cts primitive types including string int32 double decimal guid datetime among others enumeration defines map primitive values names also considered simple type enumerations supported framework version 5.0 onwards complextypes created aggregation types collection properties types define entity type definition written ebnf grammar facets used describe metadata property whether nullable default value also cardinality property i.e. whether property single valued multi valued multiplicity “ 1 ” denotes single valued property “ ” means multi-valued property example entity denoted sdl relationship type defined specifying end points multiplicities example one-to-many relationship customer orders defined ado.net entity framework uses variant structured query language named entity sql aimed writing declarative queries updates entities entity relationships – conceptual level differs sql explicit constructs joins edm designed abstract partitioning data across tables querying conceptual model facilitated entityclient classes accepts entity sql query query pipeline parses entity sql query command tree segregating query across multiple tables handed entityclient provider like ado.net data providers entityclient provider also initialized using connection object addition usual parameters data store authentication info requires sdl schema mapping information entityclient provider turn turns entity sql command tree sql query native flavor database execution query returns entity sql resultset limited tabular structure unlike ado.net resultsets entity sql enhances sql adding intrinsic support canonical functions supported entity framework compliant data providers used entity sql query also extension methods linq entities translated canonical functions independent specific database ado.net data provider receives function translates desired sql statement dbmss equivalent functionality set standard embedded functions also differences accuracy calculations therefore canonical functions supported databases canonical functions return results linq entities provider allows linq used query various rdbms data sources several database server specific providers entity framework support available entity framework v4 new methods executestorequery executestorecommand added class objectcontext visual studio feature called visualizer linq query written visual studio viewed native sql using visualizer debug session visualizer linq entities object query targeting rdbms available via visualstudiogallery
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Databases
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citrix virtual apps citrix virtual apps formerly winframe metaframe presentation server xenapp application virtualization software produced citrix systems allows windows applications accessed via individual devices shared server cloud system citrix virtual apps application virtualization software delivers centrally-hosted windows applications local devices without necessity installing flagship product citrix formerly known names winframe metaframe presentation server citrix virtual apps software uses flexcast management architecture fma proprietary architecture citrix virtualization products delivers individual applications opposed entire desktops devices also used citrix workspace deliver apps part complete virtual desktop environment citrix virtual apps windows applications used devices typically could run including macintosh computers mobile devices google chromebooks conversely enables otherwise incompatible apps run windows desktops citrix virtual apps accessed devices via citrix receiver software delivered on-premises data centers public private hybrid clouds precursor virtual apps called winframe multi-user operating system based windows nt 3.51 released 1995 winframe one first products distributed citrix stage product development citrix systems licensed windows nt 3.51 base operating system microsoft core development citrix delivered multiwin engine allowed multiple users logon execute applications winframe server citrix later license multiwin technology microsoft forming basis microsoft terminal services repackaged versions windows 95 citrix winframe client included also available citrix metaframe superseded winframe 1998 product renamed several times became metaframe xp 2002 metaframe xp presentation server 2003 rebranded presentation server 2005 products focused remote access applications server-based computing 2008 product renamed xenapp xen taken company acquisition xensource 2007 2010 2012 citrix issued two updates xenapp xenapp 6 launched 2010 included new central management console called appcenter 2012 xenapp 6.5 released update included new feature called instant app access aimed reduce application launch time 2013 version 7.0 released update combined xendesktop xenapp one application called xendesktop flex management architecture fma prior versions xenapp used company independent management architecture ima 2014 version 7.5 released xenapp separate xendesktop also built fma 2018 xenapp rebranded citrix virtual apps
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Distributed computing architecture
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paul hudak paul raymond hudak july 15 1952 – april 29 2015 american professor computer science yale university best known involvement design haskell programming language well several textbooks haskell computer music chair department also master saybrook college died april 29 2015 leukemia
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Programming language topics
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gscube gscube hardware tool released sony intended use cgi production houses consisting custom variant sixteen playstation 2 motherboards running parallel playstation 2 ps2 video game console manufactured sony computer entertainment released march 4 2000 japan followed north america europe later year unveiled year siggraph name gscube short graphics synthesizer cube used two projects film incarnation resident evil according sources sent back sony japan subsequently dismantled used prototyping visual rendering final fantasy matrix antz well flight simulator although gscube good rendering capability major bottleneck connecting external computers transfer content
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Computer architecture
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dmitri alperovitch dmitri alperovitch russian-american computer security industry executive co-founder chief technology officer crowdstrike august 2011 vice president threat research mcafee published operation shady rat report suspected chinese intrusions least 72 organizations including defense contractors businesses worldwide united nations international olympic committee alperovitch born moscow 1980 1990 parents moved maryland nuclear safety training program stayed behind ussr — law — make sure parents defect 1994 whole family moved chattanooga alperovitch earned b.s computer science 2001 m.s information security 2003 georgia institute technology alperovitch worked number computer security startups late 1990s early 2000s including e-mail security startup ciphertrust one leading inventors trustedsource reputation system upon acquisition ciphertrust secure computing 2006 led research team launched software-as-a-service business company alperovitch took vice president threat research mcafee company acquired secure computing 2008 january 2010 led investigation operation aurora chinese intrusions google two dozen companies subsequently led investigation night dragon espionage operation western multinational oil gas companies traced song zhiyue chinese national living heze city shandong province late 2011 along entrepreneur george kurtz gregg marston dmitri alperovitch co-founded became chief technology officer crowdstrike security technology company focused helping enterprises governments protect intellectual property secrets cyberespionage cybercrime crowdstrike brought board senior fbi executives shawn henry former executive assistant director ead fbi criminal cyber response services branch steve chabinsky former deputy assistant director fbi cyber division crowdstrike received 256 million funding warburg pincus accel partners google capital alperovitch awarded prestigious federal 100 award contributions u.s. federal information security recognized 2013 2015 one washingtonian magazine tech titans accomplishments field cybersecurity august 2013 selected one mit technology review top 35 innovators 35 award previously larry page sergey brin mark zuckerberg 2016 politico magazine featured one “ politico 50 ” influential thinkers doers visionaries transforming american politics 2017 fortune magazine listed alperovitch 40 40 annual ranking influential young people business along emmanuel macron mark zuckerberg serena williams senior fellow atlantic council think tank named december 2013 one foreign policy top 100 leading global thinkers along angela merkel john kerry ben bernanke jeff bezos
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Computer security
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andrew file system andrew file system afs distributed file system uses set trusted servers present homogeneous location-transparent file name space client workstations developed carnegie mellon university part andrew project originally named vice afs named andrew carnegie andrew mellon primary use distributed computing afs several benefits traditional networked file systems particularly areas security scalability one enterprise afs deployment morgan stanley exceeds 25,000 clients afs uses kerberos authentication implements access control lists directories users groups client caches files local filesystem increased speed subsequent requests file also allows limited filesystem access event server crash network outage afs uses weak consistency model read write operations open file directed locally cached copy modified file closed changed portions copied back file server cache consistency maintained callback mechanism file cached server makes note promises inform client file updated someone else callbacks discarded must re-established client server network failure including timeout re-establishing callback involves status check require re-reading file consequence file locking strategy afs support large shared databases record updating within files shared client systems deliberate design decision based perceived needs university computing environment example original email system andrew project andrew message system single file per message used like maildir rather single file per mailbox like mbox see afs buffered i/o problems handling shared databases significant feature afs volume tree files sub-directories afs mountpoints links afs volumes volumes created administrators linked specific named path afs cell created users filesystem may create directories files usual without concern physical location volume volume may quota assigned order limit amount space consumed needed afs administrators move volume another server disk location without need notify users operation even occur files volume used afs volumes replicated read-only cloned copies accessing files read-only volume client system retrieve data particular read-only copy point copy becomes unavailable clients look remaining copies users data unaware location read-only copy administrators create relocate copies needed afs command suite guarantees read-only volumes contain exact copies original read-write volume time read-only copy created file name space andrew workstation partitioned shared local name space shared name space usually mounted /afs unix filesystem identical workstations local name space unique workstation contains temporary files needed workstation initialization symbolic links files shared name space andrew file system heavily influenced version 4 sun microsystems popular network file system nfs additionally variant afs distributed file system dfs adopted open software foundation 1989 part distributed computing environment finally afs version two predecessor coda file system three major implementations transarc ibm openafs arla transarc software deprecated losing support fourth implementation exists linux kernel source code since least version 2.6.10 committed red hat fairly simple implementation still early stages development therefore incomplete january 2013 following access control list acl permissions granted permissions affect files subdirectories include additionally afs includes application acls h effect access files
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Computer file systems
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snare software snare sometimes also written snare acronym system intrusion analysis reporting environment collection software tools collect audit log data variety operating systems applications facilitate centralised log analysis enterprise agents available linux osx windows solaris microsoft sql server variety browsers snare enterprise epilog windows facilitates central collection processing windows text-based log files isa/iis snare enterprise epilog unix provides method collect text based log files linux solaris operating systems opensource agents available irix aix snare currently used hundreds thousands individuals organisations worldwide meet local federal information security guidelines associated auditing eventlog collection snare series agents began life 2001 team intersect alliance created linux kernel module implement trusted computer system evaluation criteria auditing c2 level agents windows solaris soon followed additional operating systems applications added mix time snare server software originally designed meet needs australian-based intelligence agency clients distribution restricted australia need server solution complement increasingly popular snare agents pushed intersect alliance team find overseas partners allow distribution internationally snare described 'de facto standard windows event retrieval deep roots open source movement coupled available commercial support options used small non-profit organisations right huge multinational fortune-500 companies organisations produce audit server software competes snare server software cisco sensage loglogic use recommend snare agents customers agents supported commercial open-source version available snare agents designed collect audit log data host system push data quickly possible central server servers archive analysis reporting central server either syslog server snare server appliance custom application snare agents also able push logs unidirectional network order facilitate log transfer networks low classification networks higher classification snare server appliance software-only solution provides variety analysis tools facilitate collection analysis reporting archival audit log data
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Computer security
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okular okular multiplatform document viewer developed kde community based qt kde frameworks libraries distributed part kde applications bundle originally based kpdf replaced kpdf kghostview kfax kfaxview kdvi kde 4 functionality easily embedded applications okular started google summer code 2005 piotr szymański accepted student okular identified success story 2007 season usability season okular toolbar mockup created based analysis popular document viewers usage survey ported qt 5 december 2016 version numbering jumped 0.26 1.0 okular annotation features include commenting pdf documents highlighting drawing lines geometric shapes adding textboxes stamps annotations stored separately unmodified pdf file since version 0.15 poppler 0.20 saved document standard pdf annotations text extracted text file possible select parts document copy text image clipboard features include reading text aloud using qt speech module part qt since qt 5 previously using jovie trimming white page borders setting bookmarks supports following file formats official version obeys drm restrictions pdf files default may prevent copying printing converting pdf files turned options obey drm limitations however
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Programming language topics
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klaiber law simply stated klaiber law proposes silicon wafer size dictate largest diameter ultrapure water supply piping needed within semiconductor wafer factory ultrapure water upw used extensively fabrication steps making computer microchips microchips fabricated round thin substrates silicon called wafer since 1990s pipes fittings valves used carry upw increased dramatically diameter consequently delivered volume gallons per minute usage polyvinylidene fluoride pvdf material choice larger conduits convey upw pvdf also referenced astm 5127 – 07 standard guide ultra-pure water used electronics semiconductor industries needed maintain highest qualities water early 1990s observation made dr. felix klaiber since referred klaiber ’ law recognized semiconductor jump using 100mm 150mm diameter silicon wafers largest conduits upw systems pvdf 110mm outer diameter soon followed need larger 160mm pvdf conduits next jump 200mm silicon wafers years later required 225mm pvdf conduits recently semiconductor jump 300mm wafers required need even larger upw systems using 315mm conduits since dr. klaiber earlier postulation relationship wafer size diameter pvdf conduits observed others unbeknownst libman et al. identical position klaiber law discussed 2010 presentation current hp high purity pvdf piping size limited 12 inch 305mm historically size wafer coincided diameter main lines libman questioned trend would continue 450mm wafers
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Computer architecture
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extendscript extendscript scripting language associated toolkit developed adobe systems intended use creative suite technical communication suite products dialect ecmascript 3 standard therefore similar javascript actionscript toolkit comes bundled creative suite technical communication suite editions access tools within applications like photoshop framemaker indesign effects batch-processing projects
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Programming language topics
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euslisp robot programming language euslisp lisp-based programming system built basis object orientation designed specifically developing robotics software first version ran 1986 unix-system5/ustation-e20
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Programming language topics
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domain-specific modeling domain-specific modeling dsm software engineering methodology designing developing systems computer software involves systematic use domain-specific language represent various facets system domain-specific modeling languages tend support higher-level abstractions general-purpose modeling languages require less effort fewer low-level details specify given system domain-specific modeling often also includes idea code generation automating creation executable source code directly domain-specific language models free manual creation maintenance source code means domain-specific language significantly improve developer productivity reliability automatic generation compared manual coding also reduce number defects resulting programs thus improving quality domain-specific language differs earlier code generation attempts case tools 1980s uml tools 1990s code generators modeling languages built tool vendors possible tool vendor create domain-specific language generators normal domain-specific language occur within one organization one expert developers creates modeling language generators rest developers use modeling language generator built organization use allows tight fit exact domain response changes domain domain-specific languages usually cover range abstraction levels particular domain example domain-specific modeling language mobile phones could allow users specify high-level abstractions user interface well lower-level abstractions storing data phone numbers settings likewise domain-specific modeling language financial services could permit users specify high-level abstractions clients well lower-level abstractions implementing stock bond trading algorithms domain-specific modeling also helpful reason low-level software artifacts define language one needs language write definition language model often called metamodel hence language defining modeling language meta-metamodel meta-metamodels divided two groups derived customizations existing languages developed specifically meta-metamodels derived meta-metamodels include entity relationship diagrams formal languages extended backus-naur form ebnf ontology languages xml schema meta-object facility mof strengths languages tend familiarity standardization original language ethos domain-specific modeling favors creation new language specific task unsurprisingly new languages designed meta-metamodels widely used family languages oprr goprr gopprr focus supporting things found modeling languages minimum effort many general-purpose modeling languages already tool support available form case tools domain-specific language languages tend small market size support construction bespoke case tool scratch instead tool support domain-specific language languages built based existing domain-specific language frameworks domain-specific language environments domain-specific language environment may thought metamodeling tool i.e. modeling tool used define modeling tool case tool resulting tool may either work within domain-specific language environment less commonly produced separate stand-alone program common case domain-specific language environment supports additional layer abstraction compared traditional case tool using domain-specific language environment significantly lower cost obtaining tool support domain-specific language since well-designed domain-specific language environment automate creation program parts costly build scratch domain-specific editors browsers components domain expert needs specify domain specific constructs rules domain-specific language environment provides modeling tool tailored target domain existing domain-specific language takes place domain-specific language environments either commercial metaedit+ actifsource open source gems academic gme increasing popularity domain-specific language led domain-specific language frameworks added existing ides e.g eclipse modeling project emp emf gmf microsoft dsl tools software factories unified modeling language uml general-purpose modeling language software-intensive systems designed support mostly object oriented programming consequently contrast domain-specific language languages uml used wide variety purposes across broad range domains primitives offered uml object oriented programming domain-specific languages offer primitives whose semantics familiar practitioners domain example domain automotive engineering software models represent properties anti-lock braking system steering wheel etc uml includes profile mechanism allows constrained customized specific domains platforms uml profiles use stereotypes stereotype attributes known tagged values uml 2.0 constraints restrict extend scope uml particular domain perhaps best known example customizing uml specific domain sysml domain specific language systems engineering
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Programming language topics
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online os online operating system fully multi-lingual free use web desktop written javascript using ajax windows-based desktop environment open-source applications system utilities developed upon rebox web application framework icube network solutions austrian company located vienna oos.cc short online operating system web application platform mimicked look feel classic desktop operating systems microsoft windows mac os x kde consisted various open source applications built upon so-called rebox web application framework applications could executed integrated parallel way oos could considered web desktop webtop provided basic services gui virtual file system access control management possibilities develop deploy applications online online operating system executed within web browser real operating system rather portal various web applications offering high usability flexibility project partly funded grants internetprivatstiftung austria ipa 01.08.2008 almost 20.000 users joined oos.cc community using offered featured applications development web desktop started icube network solutions 2005 followed first beta releases 2006 hence together youos eyeos considered one first publicly available systems kind first full version including core-level multi-language support file system basic set applications released public march 2007 occasion national exhibition itnt austria left beta state half year later october 2007 first release considered stable 1.0.0 published july 2007 project contained applications received several national innovation awards see gained attention mainly due comprehensive approach taken see oos.cc started national project full platform including offered applications currently available three languages german english well spanish receiving increasing coverage around world examples see current version 1.3.01 01.08.2008 project fully written javascript exclusively using dhtml techniques run web browser without additional software installation needed system implements modern kind web application model excessively using ajax communicating client components java server backend exclusively asynchronous manner aim offer users unique interaction behavior following desktop metaphor main idea web desktop also typical sort web application broadly use javascript-on-demand techniques cutting complete project source pieces loading instantly needed based technical basis rebox framework library applications oos.cc built fully flexible extensible api including gui widget set communication mechanisms server services offering general framework specific services online operating system consisted basic framework able launch javascript application using rebox library user interface based behavior windows desktop start menu task bar desktop background applications running environment server side java based web services ran serve client processes provide data relational database backend oos.cc also provided integrated development environment called developer suite allowed community build applications desktop environment based rebox see development section applications available oos.cc open source european union public licence eupl rebox development toolkit free use developing applications webtop mentioned applications published oos.cc open source based eupl installed deinstalled what-ever preferences user besides global services like multi-language support global theme support well minor tools games oos.cc offered four major services could used completely free charge next releases planned focus extensive security privacy suite dealing challenges like anonymous communication browsing well temporary mail-addresses well offering encrypted password file storage connectivity services since initial stable release oos.cc could accessed using https ensure secure communication one key focuses team right beginning offer flexible comprehensive api used develop custom applications within oos.cc also stand-alone web-applications integrate single components existing web-sites decoupling development web-related problems using rebox api web-applications development similar fashion java program elements positioned interact like high-level object oriented programming languages without taking care divs browser specific behavior communication handling framework also offers multi-language theme support existing well newly created applications allowing changing almost every aspect look feel used components according preferences users taking advantage approach one applications offered oos integrated development suite allowing directly writing executing code hence creating new programs within boundaries web computer applications oos.cc released open source thus existing programs offered imported reviewed changed locally deployed following idea every user free submit changed newly created applications included globally offered application set last release offered features like auto-completion outline-window
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Distributed computing architecture
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exfat exfat extended file allocation table file system introduced microsoft 2006 optimized flash memory usb flash drives sd cards exfat proprietary microsoft owns patents several elements design exfat used ntfs feasible solution due data-structure overhead greater file-size limit standard fat32 file system i.e 4 gib required exfat adopted sd card association default file system sdxc cards larger 32 gib 2013 samsung published gpl linux driver exfat exfat first introduced late 2006 part windows ce 6.0 embedded windows operating system vendors signing licenses exfat either embedded systems device manufacturers produce media preformatted exfat entire file allocation table fat family exfat included used embedded systems lightweight better suited solutions low memory low power requirements easily implemented firmware specifications features requirements exfat file system include exfat format allows individual files larger 4 gb facilitating long continuous recording hd video exceed 4 gb limit less hour current digital cameras using fat32 break video files multiple segments approximately 2 4 gb increase capacity increase data transferred write operation needs made efficient sdxc cards running uhs-i minimum guaranteed write speed 10 mbps exfat plays factor achieving throughput reduction file system overhead cluster allocation achieved introduction cluster bitmap elimination reduction writes fat single bit directory record indicates file contiguous telling exfat driver ignore fat optimization analogous extent file systems except applies whole files opposed contiguous parts files exfat supported windows xp windows server 2003 update kb955704 windows embedded ce 6.0 windows vista service pack 1 windows server 2008 windows 7 windows 8 windows server 2008 r2 except windows server 2008 server core windows 10 mac os x starting 10.6.5 companies integrate exfat specific group consumer devices including cameras camcorders digital photo frames flat fee mobile phones pcs networks different volume pricing model exfat supported number media devices modern flat-panel tvs media centers portable media players vendors flash media including usb pen drives compact flash cf solid-state drives ssd ship high-capacity media pre-formatted exfat file system example sandisk ships 256 gb cf cards exfat microsoft entered licensing agreements blackberry panasonic sanyo sony canon aspen avionics audiovox continental harman lg automotive bmw mac os x snow leopard 10.6.5 later create read write verify repair exfat file systems fuse-based implementation named fuse-exfat exfat-fuse read/write support available freebsd multiple linux distributions older versions mac os x kernel implementation also released written samsung initially released github unintentionally later released officially samsung compliance gpl none solutions become official part linux due patent encumbered status exfat file system implementation called exfatfilesystem based fuse-exfat available amigaos 4.1 proprietary read/write solutions licensed derived microsoft exfat implementation available android linux operating systems paragon software group tuxera xcfiles datalight proprietary full-featured implementation intended portable 32-bit systems rtfs ebs embedded software full-featured implementation embedded devices two experimental unofficial solutions available dos loadable usbexfat driver requires panasonic usb stack dos works usb storage devices open-source exfat executable exfat file system reader requires hx dos extender work native exfat real-mode dos drivers would allow usage booting exfat volumes exfat employs filename hash-based lookup phase speed certain cases described us patent 8321439 quick file name lookup using name hash document perhaps contains additional details helpful understanding file system appendix like ntfs exfat pre-allocate disk space file marking arbitrary space disk 'allocated file exfat uses two separate 64-bit length fields directory valid data length vdl indicates real size file physical data length provide improvement allocation cluster storage new file microsoft incorporated method pre-allocate contiguous clusters bypass use updating fat table december 10 2013 us patent office granted patent us8606830 one feature exfat used exfat implementation within embedded systems provides atomic transactions multiple steps updating file system metadata feature called transaction safe fat texfat granted patent us patent office us7613738 november 3 2009. exfat rest fat family file systems use indexes file names unlike ntfs uses b-trees file searching file accessed directory must sequentially searched match found file names shorter 16 characters length one file name record required entire file represented three 32-byte directory records called directory file set 256 mib sub-directory hold 2,796,202 file sets files longer names number decrease maximum based minimum three-record file set help improve sequential searching directories including root hash value file name derived file stored directory record searching file file name first converted upper case using upcase table file names case insensitive hashed using proprietary patented algorithm 16-bit 2 byte hash value record directory searched comparing hash value match found file names compared ensure proper file located case hash collisions improves performance 2 bytes compared file significantly reduces cpu cycles file names 2 characters bytes size virtually every comparison performed 2 bytes time intended file located exfat introduces metadata integrity use checksums three checksums currently use volume boot record vbr 12 sector region contains boot records bios parameter block bpb oem parameters checksum sector two vbr type regions main vbr backup vbr checksum sector checksum previous 11 sectors exception three bytes boot sector flags percent used provides integrity vbr determining vbr modified common cause could boot sector virus would also catch corruption vbr second checksum used upcase table static table never change corruption table could prevent files located table used convert filenames upper case searching locate file third checksum directory file sets multiple directory records used define single file called file set file set metadata including file name time stamps attributes address first cluster location data file lengths file name checksum taken entire file set mismatch would occur directory file set accidentally maliciously changed file system mounted integrity check conducted hashes verified mounting also includes comparison version exfat file system driver make sure driver compatible file system trying mount make sure none required directory records missing example directory record upcase table allocation bitmap required file system ca n't run missing checks fail file system mounted although certain cases may mount read-only file system provides extensibility template-based metadata definitions using generic layouts generic patterns exfat proprietary file system microsoft released specification lack documentation hampered development free open-source drivers exfat accordingly exfat support effectively limited microsoft products microsoft licensees turn inhibited exfat adoption universal exchange format interoperability requires certain results achieved particular predefined way algorithm exfat potentially requires every implementation perform certain procedures exactly way microsoft implementation procedures used microsoft implementation patented patents owned microsoft license use algorithms purchased microsoft companies including apple google samsung done however open-source ecosystem financial incentive open-source vendors purchase license algorithms regardless whether open-source including samsung leaked kernel driver source initially fraudulently rebadged gpl-licensed microsoft stated license required order implement exfat use product device unlicensed distribution exfat driver would make distributor liable financial damages driver found violated microsoft patents patents may enforceable determined legal process expensive time consuming may also possible achieve intended results without infringing microsoft patents october 2018 microsoft released 60,000 patents open invention network members linux systems exfat patents included however discussion within microsoft whether microsoft allow exfat linux devices
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Computer file systems
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arm cortex-a72 arm cortex-a72 microarchitecture implementing armv8-a 64-bit instruction set designed arm holdings austin design centre cortex-a72 3-wide decode out-of-order superscalar pipeline available sip core licensees design makes suitable integration sip cores e.g gpu display controller dsp image processor etc one die constituting system chip soc cortex-a72 announced 2015 serve successor cortex-a57 designed use 20 less power offer 90 greater performance
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Computer architecture
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google search console google search console previously google webmaster tools web service google provided free charge webmasters allows check indexing status optimize visibility websites may 20 2015 google rebranded google webmaster tools google search console january 2018 google introduced new version search console refreshed user interface improvements tools let webmasters list inbound links google webmaster tools generally much larger list inbound links discovered using link example.com search query google google tight lipped discrepancy list google webmaster tools includes nofollow links convey search engine optimization authority linked site hand list links generated link example.com type query deemed google important links controversial way google webmaster tools well google index seems routinely ignore link spam manual penalty removed google webmaster tools still display penalty another 1–3 days google search console rebrand information produced demonstrating google search console creates data points reconcile google analytics ranking data particularly within local search market webmaster services hawaii
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Web technology
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perlbal perlbal perl-based reverse proxy load balancer web server perlbal maintained group connected danga interactive program common use large web sites distribute load number servers like perl perlbal distributed gnu general public license artistic license thus free software perlbal also features so-called re-proxy mechanism allows backend webapp send back small response perlbal acts internal redirect causes get response data elsewhere often used expensive application server processes defer much simpler faster http servers serve static files freeing application server computing work commonly used conjunction mogilefs additionally plugins written support various operations may traditionally performed application layer example filter plugin developed dynamically alter palette png gif image passes proxy allowing image tinted used livejournal provide predefined page templates whose colors including baked images customized user relatively simple filtering task load balancer layer avoids overhead passing request back full application servers
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Web technology
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simultaneous authentication equals cryptography simultaneous authentication equals sae secure password-based authentication password-authenticated key agreement method sae variant dragonfly key exchange defined based diffie–hellman key exchange using finite cyclic groups primary cyclic group elliptic curve problem using diffie–hellman key exchange authentication mechanism resulting key influenced pre-shared key mac addresses peers solve authentication problem sae originally implemented use peers ieee 802.11s peers discover security enabled take part sae exchange sae completes successfully peer knows party possesses mesh password by-product sae exchange two peers establish cryptographically strong key key used authenticated mesh peering exchange ampe establish secure peering derive session key protect mesh traffic including routing traffic january 2018 wi-fi alliance announced wpa3 replacement wpa2 new standard uses 128-bit encryption wpa3-personal mode 192-bit wpa3-enterprise forward secrecy wpa3 standard also replaces pre-shared key exchange simultaneous authentication equals defined ieee 802.11-2016 resulting secure initial key exchange personal mode wi-fi alliance also claims wpa3 mitigate security issues posed weak passwords simplify process setting devices display interface
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Computer security
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json-wsp json-wsp javascript object notation web-service protocol web-service protocol uses json service description requests responses inspired json-rpc lack service description specification documentation json-rpc sparked design json-wsp description format purpose json-wsp wsdl soap idl corba describe types methods used given service also describes inter-type relations i.e nested types defines types expected method arguments types user expect receive method return values finally description opens possibility add documentation service method parameter return levels communication clients json-wsp server carried using http post requests responses json objects data content-type application/json json-wsp consists four json object specifications note json-wsp specification 1.0 still final please refer real-world example article get idea specification going structured current state actual specification kept launchpad.net rfc proposal currently created hopefully accepted within couple months service-locator service endpoint url accepts json-wsp post request objects service-name service name case sensitive identifies specific service exposed specific server doc_lines doc-string contained doc_lines list reflects single line documentation relates parent object doc_lines.. request object contains information method invoke arguments invoke method also stores information type version optional mirror value used send information client reflected server returned unchanged response object reflection value feature allows clients send multiple requests method send request identification values intercepted client response handler often necessary javascript one request processed simultaneously server response order unknown client reflection value unchanged server reflection request object mirror value marked optional client controls via request whether fault-code meanings possible fault-codes attachment type new json-wsp used anywhere description primitive type requests responses involve attachments message format must multipart/related attachments transported mimeparts media type application/octet-stream content-transfer-encoding raw binary mimeparts must unique content-id entity headers attachment values json-wsp request/response objects must match regular expression ^cid .+ capture group maps one mimepart content-id following example shows simple json-wsp description attachments could look like request method upload described could look like
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Web technology
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microsoft layer unicode microsoft layer unicode mslu software library windows software developers simplify creating unicode-aware applications windows 95 windows 98 windows also known unicows unicode windows 95/98/me systems unicows.dll even cows microsoft describes providing layer win32 api windows 95/98/me write single unicode version application run properly platforms previously software developers either provide two separate versions application perform complex string translations api decisions runtime mslu announced march 2001 first available july 2001 edition microsoft platform sdk arguably long peak popularity windows 95/98/me codename godot reference play waiting godot centered around failure man named godot appear endless wait felt long overdue normally windows api provides ansi w wide-character versions functions windows 95/98/me versions implemented attempting call w version fail error code indicates function unimplemented windows nt/2000/xp/2003 w versions implemented however operating system generally internally implements w version natively version usually translation thunk w version adding unicows.lib link command-line kernel32.lib advapi32.lib supported win32 system link library linker resolve referenced symbols one provided unicows.lib instead wide-character function called first time runtime function stub unicows.lib first receives control decides running windows 95/98/me system technique application linked mslu windows 95/98/me systems need unicows.dll runtime operating systems slight performance penalty first function call common problem encountered occurs updaters uninstallers rename delete file oledlg.dll preventing operating system loading unicows.dll results applications openoffice.org reporting application start one required libraries found occurs even unicows.dll installed system
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Operating systems
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disk formatting disk formatting process preparing data storage device hard disk drive solid-state drive floppy disk usb flash drive initial use cases formatting operation may also create one new file systems first part formatting process performs basic medium preparation often referred low-level formatting partitioning common term second part process making data storage device visible operating system third part process usually termed high-level formatting often refers process generating new file system operating systems parts three processes combined repeated different levels term format understood mean operation new disk medium fully prepared store files general rule formatting disk leaves existing data disk medium might recoverable special tools special tools remove user data single overwrite files free space block contiguous number bytes minimum unit storage read written disk disk driver earliest disk drives fixed block sizes e.g ibm 350 disk storage unit late 1950s block size 100 6 bit characters starting 1301 ibm marketed subsystems featured variable block sizes particular track could blocks different sizes disk subsystems ibm system/360 expanded concept form count key data ckd later extended count key data eckd however use variable block size hdds fell use 1990s one last hdds support variable block size ibm 3390 model 9 announced may 1993 modern hard disk drives serial attached scsi sas serial ata sata drives appear interfaces contiguous set fixed-size blocks many years 512 bytes long beginning 2009 accelerating 2011 major hard disk drive manufacturers began releasing hard disk drive platforms using advanced format 4096 byte logical blocks floppy disks generally used fixed block sizes sizes function host os interaction controller particular type media e.g. 5¼-inch dsdd would different block sizes depending upon host os controller optical discs generally use fixed block sizes formatting disk use operating system applications typically involves three different processes low-level format floppy disks early hard disks performed disk drive controller standard 1.44 mb floppy disk low-level formatting normally writes 18 sectors 512 bytes 160 tracks 80 side floppy disk providing 1,474,560 bytes storage disk physical sectors actually larger 512 bytes addition 512 byte data field include sector identifier field crc bytes cases error correction bytes gaps fields additional bytes normally included quoted figure overall storage capacity disk different low-level formats used media example large records used cut inter-record gap size several freeware shareware free software programs e.g gparted fdformat nformat 2m allowed considerably control formatting allowing formatting high-density 3.5 disks capacity 2 mb techniques used include linux supports variety sector sizes dos windows support large-record-size dmf-formatted floppy format hard disk drives prior 1990s typically separate disk controller defined data encoded media media drive and/or controller possibly procured separate vendors users often able perform low-level formatting separate procurement also potential incompatibility separate components subsystem would reliably store data user instigated low-level formatting llf hard disk drives common minicomputer personal computer systems 1990s ibm mainframe system vendors typically supplied hard disk drives media case removable media hdds low-level format typically involved subdividing track disk one blocks would contain user data associated control information different computers used different block sizes ibm notably used variable block sizes popularity ibm pc caused industry adopt standard 512 user data bytes per block middle 1980s depending upon system low-level formatting generally done operating system utility ibm compatible pcs used bios invoked using ms-dos debug program transfer control routine hidden different addresses different bioses starting late 1980s driven volume ibm compatible pcs hdds became routinely available pre-formatted compatible low-level format time industry moved historical dumb bit serial interfaces modern intelligent bit serial interfaces word serial interfaces wherein low level format performed factory today end-user cases never perform low-level formatting ide ata hard drive fact often possible modern hard drives formatting done servowriter disk assembled drive factory generally impossible perform complete llf modern hard drives since mid-1990s outside factory term low-level format still used could called reinitialization hard drive factory configuration even terms may misunderstood present ambiguity term low-level format seems due inconsistent documentation web sites belief many users process high-level file system format must called low-level format since much low level formatting process today performed factory various drive manufacturers describe reinitialization software llf utilities web sites since users generally way determine difference complete llf reinitialization simply observe running software results hard disk must high-level formatted misinformed user mixed signals various drive manufacturers perpetuated error note whatever possible misuse terms may exist search hard drive manufacturers web sites terms many sites make reinitialization utilities available possibly bootable floppy diskette cd image files overwrite every byte check damaged sectors hard disk reinitialization include identifying sparing possible sectors written read back drive correctly term however used refer portion process every sector drive written usually writing specific value every addressable location disk traditionally physical sectors initialized fill value codice_1 per int 1eh disk parameter table dpt format ibm compatible machines value also used atari portfolio 8-inch cp/m floppies typically came pre-formatted value codice_2 way digital research value also used atari st amstrad formatted floppies amstrad otherwise used codice_3 fill value modern formatters wipe hard disks value codice_4 instead sometimes also called zero-filling whereas value codice_5 used flash disks reduce wear latter value typically also default value used rom disks reformatted advanced formatting tools allow configuring fill value one popular method performing zero-fill operation hard disk writing zero-value bytes drive using unix dd utility /dev/zero stream input file drive specific partition output file command may take many hours complete erase files file systems another method scsi disks may use sg_format command issue low-level scsi format unit command zero-filling drive necessarily secure method erasing sensitive data preparing drive use encrypted filesystem zero-filling voids plausible deniability process partitioning process writing information blocks storage device medium allows access operating system operating systems allow device medium appear multiple devices i.e partitioned multiple devices ms-dos microsoft windows unix-based operating systems bsd linux mac os x normally done partition editor fdisk gnu parted disk utility operating systems support multiple partitions current ibm mainframe oss derived os/360 dos/360 z/os z/vse done init command ickdsf utility oss support single partition per device called volume ickdsf functions include creating volume label writing record 0 every track floppy disks partitioned however depending upon os may require volume information order accessed os partition editors ickdsf today handle low level functions hdds optical disc drives writing timing marks reinitialize modern disk degaussed otherwise lost factory formatting high-level formatting process setting empty file system disk partition logical volume pcs installing boot sector fast operation sometimes referred quick formatting entire logical drive partition may optionally scanned defects may take considerable time case floppy disks high- low-level formatting customarily performed one pass disk formatting software 8-inch floppies typically came low-level formatted filled format filler value codice_2 since 1990s 5.25-inch 3.5-inch floppies shipped pre-formatted factory dos fat12 floppies current ibm mainframe operating systems derived os/360 dos/360 may done part allocating file utility specific file system older access methods fly new data written host protected area sometimes referred hidden protected area area hard drive high level formatted area normally visible operating system os reformatting high-level formatting performed functioning disk drive free medium contents reformatting unique operating system actually done existing data varies os important aspect process frees disk space use data actually erase everything requires overwriting block data medium something done many high-level formatting utilities reformatting often carries implication operating system software reinstalled format complete rather fixing installation suffering malfunction security compromise may necessary simply reformat everything start scratch various colloquialisms exist process wipe reload nuke pave reimage etc format command ms-dos pc dos os/2 microsoft windows disk formatting performed codice_7 command codice_7 program usually asks confirmation beforehand prevent accidental removal data versions dos undocumented codice_9 option used usual confirmation skipped format begins right away wm/formatc macro virus uses command format drive c soon document opened unconditional format also codice_10 parameter performs unconditional format circumstances overwrites entire partition preventing recovery data software note however codice_10 switch works reliably floppy diskettes see image right technically unless codice_12 used floppies always low level formatted addition high-level formatted certain circumstances hard drive partitions however codice_10 switch merely prevents creation codice_14 information partition formatted otherwise leaving partition contents entirely intact still disk marked deleted cases user data remain ripe recovery specialist tools encase disk editors reliance upon codice_10 secure overwriting hard drive partitions therefore inadvisable purpose-built tools dban considered instead overwriting windows vista upwards non-quick format overwrite goes case windows xp os/2 os/2 use codice_16 parameter specifies long format format overwrite entire partition logical drive enhances ability chkdsk recover files high-level formatting disks systems traditionally done using codice_17 command linux potentially systems well codice_17 typically wrapper around filesystem-specific commands name codice_19 fsname name filesystem format disk filesystems supported certain implementations codice_17 manipulation tools example ntfsprogs provides format utility ntfs filesystem unix unix-like operating systems higher-level formatting tools usually purpose making disk formatting easier and/or allowing user partition disk tool examples include gnu parted various gui frontends gparted kde partition manager disk utility application mac os x file deletion operating system data disk fully erased every high-level format instead area disk containing data merely marked available retains old data overwritten disk formatted different file system one previously existed partition data may overwritten would n't file system used however file systems e.g. ntfs fat file indexes mfts ntfs inodes ext2/3 etc may written exact locations partition size increased even fat file systems overwrite data beginning new partition perspective preventing recovery sensitive data recovery tools data must either completely overwritten every sector random data format format program must perform overwriting dos codice_21 command floppy diskettes filling every data sector format filler byte value typically codice_1 however applications tools especially used forensic information technology recover data conventionally erased order avoid recovery sensitive data governmental organization big companies use information destruction methods like gutmann method average users also special applications perform complete data destruction overwriting previous information although applications perform multiple writes assure data erasure single write old data generally needed modern hard disk drives ata secure erase performed disk utilities quickly thoroughly wipe drives degaussing another option however may render drive unusable
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Computer file systems
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nexus driver term nexus driver refers bus device driver interfaces leaf drivers specific i/o bus provides low-level integration i/o bus
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Operating systems
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stuxnet stuxnet malicious computer worm first uncovered 2010 thought development since least 2005 stuxnet targets scada systems believed responsible causing substantial damage iran nuclear program although neither country openly admitted responsibility worm believed jointly built american/israeli cyberweapon stuxnet specifically targets programmable logic controllers plcs allow automation electromechanical processes used control machinery industrial processes including centrifuges separating nuclear material exploiting four zero-day flaws stuxnet functions targeting machines using microsoft windows operating system networks seeking siemens step7 software stuxnet reportedly compromised iranian plcs collecting information industrial systems causing fast-spinning centrifuges tear apart stuxnet design architecture domain-specific could tailored platform attacking modern supervisory control data acquisition scada plc systems e.g. factory assembly lines power plants majority reside europe japan us stuxnet reportedly ruined almost one fifth iran nuclear centrifuges targeting industrial control systems worm infected 200,000 computers caused 1,000 machines physically degrade stuxnet three modules worm executes routines related main payload attack link file automatically executes propagated copies worm rootkit component responsible hiding malicious files processes preventing detection presence stuxnet typically introduced target environment via infected usb flash drive thereby crossing air gap worm propagates across network scanning siemens step7 software computers controlling plc absence either criterion stuxnet becomes dormant inside computer conditions fulfilled stuxnet introduces infected rootkit onto plc step7 software modifying code giving unexpected commands plc returning loop normal operations system values feedback users 2015 kaspersky lab noted equation group used two zero-day attacks prior use stuxnet commented similar type usage exploits together different computer worms around time indicates equation group stuxnet developers either working closely together stuxnet discovered sergey ulasen initially spread via microsoft windows targeted siemens industrial control systems first time hackers targeted industrial systems first publicly known intentional act cyberwarfare implemented first discovered malware spies subverts industrial systems first include programmable logic controller plc rootkit worm initially spreads indiscriminately includes highly specialized malware payload designed target siemens supervisory control data acquisition scada systems configured control monitor specific industrial processes stuxnet infects plcs subverting step-7 software application used reprogram devices different variants stuxnet targeted five iranian organizations probable target widely suspected uranium enrichment infrastructure iran symantec noted august 2010 60 infected computers worldwide iran siemens stated worm caused damage customers iran nuclear program uses embargoed siemens equipment procured secretly damaged stuxnet kaspersky lab concluded sophisticated attack could conducted nation-state support f-secure chief researcher mikko hyppönen asked possible nation-state support involved agreed would look like yes may 2011 pbs program need know cited statement gary samore white house coordinator arms control weapons mass destruction said 're glad iranians trouble centrifuge machine – us allies – everything make sure complicate matters offering winking acknowledgement us involvement stuxnet according daily telegraph showreel played retirement party head israel defense forces idf gabi ashkenazi included references stuxnet one operational successes idf chief staff 1 june 2012 article new york times said stuxnet part us israeli intelligence operation called operation olympic games started president george w. bush expanded president barack obama 24 july 2012 article chris matyszczyk cnet reported atomic energy organization iran e-mailed f-secure chief research officer mikko hyppönen report new instance malware 25 december 2012 iranian semi-official news agency announced cyberattack stuxnet time industries southern area country virus targeted power plant industries hormozgan province recent months according expert eugene kaspersky worm also infected nuclear power plant russia kaspersky noted however since power plant connected public internet system remain safe worm first identified security company virusblokada mid-june 2010 journalist brian krebs blog posting 15 july 2010 first widely read report worm original name given virusblokada rootkit.tmphider symantec however called w32.temphid later changing w32.stuxnet current name derived combination keywords software .stub mrxnet.sys reason discovery time attributed virus accidentally spreading beyond intended target natanz plant due programming error introduced update led worm spreading engineer computer connected centrifuges spreading engineer returned home connected computer internet kaspersky lab experts first estimated stuxnet started spreading around march april 2010 first variant worm appeared june 2009 15 july 2010 day worm existence became widely known distributed denial-of-service attack made servers two leading mailing lists industrial-systems security attack unknown source likely related stuxnet disabled one lists thereby interrupted important source information power plants factories hand researchers symantec uncovered version stuxnet computer virus used attack iran nuclear program november 2007 developed early 2005 iran still setting uranium enrichment facility second variant substantial improvements appeared march 2010 apparently authors believed stuxnet spreading fast enough third minor improvements appeared april 2010 worm contains component build time-stamp 3 february 2010 united kingdom 25 november 2010 sky news reported received information anonymous source unidentified security organization stuxnet variation worm traded black market study spread stuxnet symantec showed main affected countries early days infection iran indonesia india iran reported beefed cyberwar capabilities following stuxnet attack suspected retaliatory attacks us banks unlike malware stuxnet little harm computers networks meet specific configuration requirements attackers took great care make sure designated targets hit ... marksman job worm promiscuous makes inert siemens software found infected computers contains safeguards prevent infected computer spreading worm three others erase 24 june 2012 targets stuxnet contains among things code man-in-the-middle attack fakes industrial process control sensor signals infected system shut due detected abnormal behavior complexity unusual malware worm consists layered attack three different systems stuxnet attacked windows systems using unprecedented four zero-day attacks plus cplink vulnerability vulnerability used conficker worm initially spread using infected removable drives usb flash drives contain windows shortcut files initiate executable code worm uses exploits techniques peer-to-peer rpc infect update computers inside private networks directly connected internet number zero-day exploits used unusual highly valued malware creators typically make use thus simultaneously make visible four different zero-day exploits worm amongst exploits remote code execution computer printer sharing enabled lnk/pif vulnerability file execution accomplished icon viewed windows explorer negating need user interaction stuxnet unusually large half megabyte size written several different programming languages including c c++ also irregular malware windows component malware promiscuous spreads relatively quickly indiscriminately malware user-mode kernel-mode rootkit capability windows device drivers digitally signed private keys two certificates stolen separate well-known companies jmicron realtek located hsinchu science park taiwan driver signing helped install kernel-mode rootkit drivers successfully without users notified therefore remained undetected relatively long period time compromised certificates revoked verisign two websites denmark malaysia configured command control servers malware allowing updated industrial espionage conducted uploading information domain names subsequently redirected dns service provider dynadot part global effort disable malware according researcher ralph langner installed windows system stuxnet infects project files belonging siemens wincc/pcs 7 scada control software step 7 subverts key communication library wincc called codice_1 intercepts communications wincc software running windows target siemens plc devices software able configure program two connected via data cable way malware able install plc devices unnoticed subsequently mask presence wincc control software attempts read infected block memory plc system malware furthermore used zero-day exploit wincc/scada database software form hard-coded database password entirety stuxnet code yet disclosed payload targets scada configurations meet criteria programmed identify stuxnet requires specific slave variable-frequency drives frequency converter drives attached targeted siemens s7-300 system associated modules attacks plc systems variable-frequency drives two specific vendors vacon based finland fararo paya based iran furthermore monitors frequency attached motors attacks systems spin 807 hz 1,210 hz industrial applications motors parameters diverse may include pumps gas centrifuges stuxnet installs malware memory block db890 plc monitors profibus messaging bus system certain criteria met periodically modifies frequency 1,410 hz 2 hz 1,064 hz thus affects operation connected motors changing rotational speed also installs rootkit – first documented case platform – hides malware system masks changes rotational speed monitoring systems siemens released detection removal tool stuxnet siemens recommends contacting customer support infection detected advises installing microsoft updates security vulnerabilities prohibiting use third-party usb flash drives siemens also advises immediately upgrading password access codes worm ability reprogram external plcs may complicate removal procedure symantec liam o'murchu warns fixing windows systems may completely solve infection thorough audit plcs may necessary despite speculation incorrect removal worm could cause damage siemens reports first four months since discovery malware successfully removed systems 22 customers without adverse impact prevention control system security incidents viral infections like stuxnet topic addressed public private sector us department homeland security national cyber security division ncsd operates control system security program cssp program operates specialized computer emergency response team called industrial control systems cyber emergency response team ics-cert conducts biannual conference provides training publishes recommended practices provides self-assessment tool part department homeland security plan improve american computer security 2008 idaho national laboratory inl worked siemens identify security holes company widely used process control system 7 pcs 7 software step 7 july 2008 inl siemens publicly announced flaws control system chicago conference stuxnet exploited holes 2009 several industry organizations professional societies published standards best practice guidelines providing direction guidance control system end-users establish control system security management program basic premise documents share prevention requires multi-layered approach often referred defense-in-depth layers include policies procedures awareness training network segmentation access control measures physical security measures system hardening e.g. patch management system monitoring anti-virus intrusion prevention system ips standards best practices also recommend starting risk analysis control system security assessment experts believe stuxnet required largest costliest development effort malware history developing many capabilities would required team highly capable programmers in-depth knowledge industrial processes interest attacking industrial infrastructure eric byres years experience maintaining troubleshooting siemens systems told wired writing code would taken many man-months man-years symantec estimates group developing stuxnet would consisted five thirty people would taken six months prepare guardian bbc new york times claimed unnamed experts studying stuxnet believe complexity code indicates nation-state would capabilities produce self-destruct safeguards within code implied western government responsible least responsible development however software security expert bruce schneier initially condemned 2010 news coverage stuxnet hype stating almost entirely based speculation subsequent research schneier stated 2012 conclusively link stuxnet centrifuge structure natanz nuclear enrichment lab iran ralph langner researcher identified stuxnet infected plcs first speculated publicly september 2010 malware israeli origin targeted iranian nuclear facilities however langner recently ted talk recorded february 2011 stated opinion mossad involved leading force israel leading force behind stuxnet cyber superpower – one united states kevin hogan senior director security response symantec reported majority infected systems iran 60 led speculation may deliberately targeting high-value infrastructure iran including either bushehr nuclear power plant natanz nuclear facility langner called malware one-shot weapon said intended target probably hit although admitted speculation another german researcher spokesman german-based chaos computer club frank rieger first speculate natanz target according israeli newspaper haaretz september 2010 experts iran computer security specialists increasingly convinced stuxnet meant sabotage uranium enrichment facility natanz – centrifuge operational capacity dropped past year 30 percent 23 november 2010 announced uranium enrichment natanz ceased several times series major technical problems serious nuclear accident supposedly shutdown centrifuges occurred site first half 2009 speculated forced head iran atomic energy organization gholam reza aghazadeh resign statistics published federation american scientists fas show number enrichment centrifuges operational iran mysteriously declined 4,700 3,900 beginning around time nuclear incident wikileaks mentioned would occurred institute science international security isis suggests report published december 2010 stuxnet reasonable explanation apparent damage natanz may destroyed 1,000 centrifuges 10 percent sometime november 2009 late january 2010 authors conclude isis report notes iranian authorities attempted conceal breakdown installing new centrifuges large scale worm worked first causing infected iranian ir-1 centrifuge increase normal operating speed 1,064 hertz 1,410 hertz 15 minutes returning normal frequency twenty-seven days later worm went back action slowing infected centrifuges hundred hertz full 50 minutes stresses excessive slower speeds caused aluminium centrifugal tubes expand often forcing parts centrifuges sufficient contact destroy machine according washington post iaea cameras installed natanz facility recorded sudden dismantling removal approximately 900–1,000 centrifuges time stuxnet worm reportedly active plant iranian technicians however able quickly replace centrifuges report concluded uranium enrichment likely briefly disrupted 15 february 2011 institute science international security released report concluding associated press reported semi-official iranian students news agency released statement 24 september 2010 stating experts atomic energy organization iran met previous week discuss stuxnet could removed systems according analysts david albright western intelligence agencies attempting sabotage iranian nuclear program time head bushehr nuclear power plant told reuters personal computers staff plant infected stuxnet state-run newspaper iran daily quoted reza taghipour iran telecommunications minister saying caused serious damage government systems director information technology council iranian ministry industries mines mahmud liaii said electronic war launched iran ... computer worm designed transfer data production lines industrial plants locations outside iran response infection iran assembled team combat 30,000 ip addresses affected iran official said infection fast spreading iran problem compounded ability stuxnet mutate iran set systems clean infections advised using siemens scada antivirus since suspected antivirus actually embedded codes update stuxnet instead eradicating according hamid alipour deputy head iran government information technology company attack still ongoing new versions virus spreading reported company begun cleanup process iran sensitive centres organizations anticipated could root virus within one two months virus stable since started cleanup process three new versions spreading told islamic republic news agency 27 september 2010 29 november 2010 iranian president mahmoud ahmadinejad stated first time computer virus caused problems controller handling centrifuges natanz facilities according reuters told reporters news conference tehran succeeded creating problems limited number centrifuges software installed electronic parts day two iranian nuclear scientists targeted separate nearly simultaneous car bomb attacks near shahid beheshti university tehran majid shahriari quantum physicist killed fereydoon abbasi high-ranking official ministry defense seriously wounded wired speculated assassinations could indicate whoever behind stuxnet felt sufficient stop nuclear program wired article suggested iranian government could behind assassinations january 2010 another iranian nuclear scientist physics professor tehran university killed similar bomb explosion 11 january 2012 director natanz nuclear enrichment facility mostafa ahmadi roshan killed attack quite similar one killed shahriari analysis fas demonstrates iran enrichment capacity grew 2010 study indicated iran centrifuges appeared performing 60 better previous year would significantly reduce tehran time produce bomb-grade uranium fas report reviewed official iaea affirmed study european us officials along private experts told reuters iranian engineers successful neutralizing purging stuxnet country nuclear machinery given growth iranian enrichment capability 2010 country may intentionally put misinformation cause stuxnet creators believe worm successful disabling iranian nuclear program actually israel unit 8200 speculated country behind stuxnet many media reports experts richard a. falkenrath former senior director policy plans within us office homeland security yossi melman covers intelligence israeli daily newspaper haaretz writing book israeli intelligence also suspected israel involved noting meir dagan former 2011 head national intelligence agency mossad term extended 2009 said involved important projects additionally israel expects iran nuclear weapon 2014 2015 – least three years later earlier estimates – without need israeli military attack iranian nuclear facilities seem know something time originally thought added israel publicly commented stuxnet attack confirmed cyberwarfare among pillars defense doctrine military intelligence unit set pursue defensive offensive options questioned whether israel behind virus fall 2010 israeli officials broke wide smiles fueling speculation government israel involved genesis american presidential advisor gary samore also smiled stuxnet mentioned although american officials indicated virus originated abroad according telegraph israeli newspaper haaretz reported video celebrating operational successes gabi ashkenazi retiring idf chief staff shown retirement party included references stuxnet thus strengthening claims israel security forces responsible 2009 year stuxnet discovered scott borg united states cyber-consequences unit us-ccu suggested israel might prefer mount cyber-attack rather military strike iran nuclear facilities late 2010 borg stated israel certainly ability create stuxnet little downside attack would virtually impossible prove tool like stuxnet israel obvious weapon choice iran uses p-1 centrifuges natanz design a. q. khan stole 1976 took pakistan black market nuclear-proliferation network sold p-1s among customers iran experts believe israel also somehow acquired p-1s tested stuxnet centrifuges installed dimona facility part nuclear program equipment may united states received p-1s libya former nuclear program also referred several clues code concealed reference word myrtus believed refer myrtle tree hadassah hebrew hadassah birth name former jewish queen persia queen esther however may myrtus reference simply misinterpreted reference scada components known rtus remote terminal units reference actually rtus –a management feature scada also number 19790509 appears code might refer date 1979 may 09 day habib elghanian persian jew executed tehran another date appears code 24 september 2007 day iran president mahmoud ahmadinejad spoke columbia university made comments questioning validity holocaust data conclusive since noted symantec ... attackers would natural desire implicate another party also testimony involvement united states collaboration israel one report stating vanishingly little doubt played role creating worm reported united states one secret programs initiated bush administration accelerated obama administration sought destroy iran nuclear program novel methods undermining iranian computer systems diplomatic cable obtained wikileaks showed united states advised target iran nuclear capabilities 'covert sabotage new york times article early january 2009 credited unspecified program preventing israeli military attack iran efforts focused ways destabilize centrifuges wired article claimed stuxnet believed created united states fact john bumgarner former intelligence officer member united states cyber-consequences unit us-ccu published article prior stuxnet discovered deciphered outlined strategic cyber strike centrifuges suggests cyber attacks permissible nation states operating uranium enrichment programs violate international treaties gives credibility claims bumgarner pointed centrifuges used process fuel nuclear weapons key target cybertage operations made destroy manipulating rotational speeds march 2012 interview 60 minutes retired us air force general michael hayden – served director central intelligence agency national security agency – denying knowledge created stuxnet said believed good idea carried downside legitimized use sophisticated cyber weapons designed cause physical damage hayden said take look ... maybe even attempt turn purposes report sean mcgurk former cybersecurity official department homeland security noted stuxnet source code could downloaded online modified directed new target systems speaking stuxnet creators said opened box demonstrated capability ... something put back april 2011 iranian government official gholam reza jalali stated investigation concluded united states israel behind stuxnet attack frank rieger stated three european countries intelligence agencies agreed stuxnet joint united states-israel effort code windows injector plc payload differ style likely implying collaboration experts believe us-israel cooperation unlikely level trust two countries ’ intelligence military establishments high wired magazine article us general keith b. alexander stated cyber warriors already launched first attack cyber weapon came known stuxnet created built nsa partnership cia israeli intelligence mid-2000s china jordan france possibilities siemens may also participated langner speculated infection may spread usb drives belonging russian contractors since iranian targets accessible via internet sandro gaycken free university berlin argued attack iran ruse distract stuxnet real purpose according broad dissemination 100,000 industrial plants worldwide suggests field test cyber weapon different security cultures testing preparedness resilience reactions highly valuable information cyberwar unit united kingdom denied involvement worm creation stratfor documents released wikileaks suggest international security firm 'stratfor believe israel behind stuxnet – ca n't assume stuxnet capable blast well july 2013 edward snowden claimed stuxnet cooperatively developed united states israel according report reuters nsa also tried sabotage north korea nuclear program using version stuxnet operation reportedly launched tandem attack targeted iranian centrifuges 2009–10 north korean nuclear program shares many similarities iranian developed technology transferred pakistani nuclear scientist a.q khan effort failed however north korea extreme secrecy isolation made impossible introduce stuxnet nuclear facility gholamreza jalali iran chief national passive defence organisation npdo claims country fended stuxnet-like attack targeting country telecom infrastructure iran telecommunications minister mohammad-javad azari jahromi since accused israel orchestrating attack iran plans sue israel international court justice icj also willing launch retaliation attack latter n't mend ways november 2013 article foreign policy magazine claims existence earlier much sophisticated attack centrifuge complex natanz focused increasing centrifuge failure rate long time period stealthily inducing uranium hexafluoride gas overpressure incidents malware capable spreading physically installed probably previously contaminated field equipment used contractors working siemens control systems within complex clear whether attack attempt successful followed different simpler conventional attack indicative 1 september 2011 new worm found thought related stuxnet laboratory cryptography system security crysys budapest university technology economics analyzed malware naming threat duqu symantec based report continued analysis threat calling nearly identical stuxnet completely different purpose published detailed technical paper main component used duqu designed capture information keystrokes system information exfiltrated data may used enable future stuxnet-like attack 28 december 2011 kaspersky lab director global research analysis spoke reuters recent research results showing platform stuxnet duqu originated 2007 referred tilded due ~d beginning file names also uncovered research possibility three variants based tilded platform may 2012 new malware flame found thought related stuxnet researchers named program flame name one modules analysing code flame kaspersky lab said strong relationship flame stuxnet early version stuxnet contained code propagate infections via usb drives nearly identical flame module exploits vulnerability december 2017 reported safety systems unidentified power station believed saudi arabia compromised triconex industrial safety technology made schneider electric se targeted believed state sponsored attack computer security company symantec claimed malware known triton exploited vulnerability computers running microsoft windows operating system since 2010 extensive international media coverage stuxnet aftermath early commentary economist pointed stuxnet new kind cyber-attack 8 july 2011 wired published article detailing network security experts able decipher origins stuxnet piece kim zetter claimed stuxnet cost–benefit ratio still question later commentators tended focus strategic significance stuxnet cyber weapon following wired piece holger stark called stuxnet first digital weapon geopolitical importance could change way wars fought meanwhile eddie walsh referred stuxnet world newest high-end asymmetric threat ultimately claim extensive media coverage afforded stuxnet served advertisement vulnerabilities used various cybercriminal groups may case media coverage also increased awareness cyber security threats alex gibney 2016 documentary zero days covers phenomenon around stuxnet 2016 revealed general james cartwright former head u.s. strategic command leaked information related stuxnet later pleaded guilty lying fbi agents pursuing investigation leak 17 january 2017 granted full pardon case president obama thereby expunging conviction
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Computer security
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wimg cpu wimg acronym describes memory/cache attributes powerpc/power isa letter wimg represents one bit access attribute specifically write-through access w cache-inhibited access memory coherence guarded g set 1 indicates write-through access set 0 indicates access address non-write set 1 indicates cache-inhibited access set 0 indicates access address cacheable external caches look-aside directory protocols use bit determine actions value bit must accesses processors given address carried ax field.1 however i/o peripheral may access bit set 1 address accessed processors bit set 0 aliasing bit considered error combination w=i=1 supported set 1 requires memory coherence must enforced regardless values qualifiers specifically cache hierarchies must snoop transaction even bit set bit set presentation transaction snooper snooper must ignore transaction however originator transaction may ignore even 0 cache-inhibited guarded writes g 1 issued given processor must performed system order issuance processor regardless coherency qualifier regardless addresses carried transactions
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Computer architecture
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william cheswick william r. bill cheswick also known ches computer security networking researcher cheswick graduated lawrenceville school 1970 received b.s fundamental science 1975 lehigh university lehigh working doug price steve lidie cheswick co-authored senator line-oriented text editor cheswick early career included contracting bethlehem pa 1975 1977 programmer american newspaper publishers association research institute easton pa 1976 1977 systems programmer computer sciences corporation warminster pa 1977 1978 following cheswick joined systems computer technology corporation served systems programmer consultant 1978 1987 much cheswick early career related expertise control data corporation cdc mainframes operating systems scope nos related compass assembly language cheswick initially worked cdc systems student lehigh university cheswick joined bell labs 1987 shortly thereafter steven m. bellovin created one world first network firewalls resulting research papers lead publication seminal book firewalls internet security one first describe architecture firewall detail cheswick bellovin also created one world first honeypots course detecting trapping attempted intruder network 1998 cheswick still bell labs controlled lucent started internet mapping project assisted hal burch research allowed large scale mapping internet first time using tracerouting techniques learn connectivity graph global networks work ultimately led founding 2000 spinoff company lumeta cheswick co-founder held title chief scientist joined shannon lab 2007 remained 2012 cheswick currently lives new jersey wife two children home farmhouse flemington electronic smart house equipped voice synthesizer reports relevant information mailbox status evening stock news cheswick developed interactive exhibits science museums including liberty science center new jersey cheswick also enjoys model rocketry lock picking electronic physical interested developing better passwords discussed article rethinking passwords communications acm 56.2 2013 cheswick also seeking permission filmmakers publish visualizations movies
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Computer security
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power4 power4 microprocessor developed international business machines ibm implemented 64-bit powerpc powerpc instruction set architectures released 2001 power4 succeeded power3 rs64 microprocessors used rs/6000 as/400 computers ending separate development powerpc microprocessors as/400 power4 multicore microprocessor two cores single die first non-embedded microprocessor power4 chip first commercially available multiprocessor chip original power4 clock speed 1.1 1.3 ghz enhanced version power4+ reached clock speed 1.9 ghz powerpc 970 derivative power4 power4 unified l2 cache divided three equal parts independent l2 controller feed 32 bytes data per cycle core interface unit ciu connects l2 controller either data cache instruction cache either two processors non-cacheable nc unit responsible handling instruction serializing functions performing noncacheable operations storage topology l3 cache controller actual memory off-chip gx bus controller controls i/o device communications two 4-byte wide gx buses one incoming outgoing fabric controller master controller network buses controlling communications l1/l2 controllers communications power4 chips 4-way 8-way 16-way 32-way power4 mcm trace-and-debug used first failure data capture provided also built self test function bist performance monitoring unit pmu power-on reset por supported power4 implements superscalar microarchitecture high-frequency speculative out-of-order execution using eight independent execution units two floating-point units fp1-2 two load-store units ld1-2 two fixed-point units fx1-2 branch unit br conditional-register unit cr execution units complete eight operations per clock including br cr units pipeline stages power4 also came configuration using multi-chip module mcm containing four power4 dies single package 128 mb shared l3 ecc cache per mcm power4+ released 2003 improved version power4 ran 1.9 ghz contained 184 million transistors measured 267 mm fabricated 0.13 µm soi cmos process eight layers copper interconnect
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Computer architecture
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medium access control ieee 802 lan/man standards medium access control mac sublayer layer controls hardware responsible interaction wired optical wireless transmission medium mac sublayer logical link control llc sublayer together make data link layer within data link layer llc provides flow control multiplexing logical link i.e ethertype 802.1q vlan tag etc mac provides flow control multiplexing transmission medium two sublayers together correspond layer 2 osi model compatibility reasons llc optional implementations ieee 802.3 frames raw compulsory implementations ieee 802 physical layer standards within hierarchy osi model ieee 802 standards mac sublayer provides control abstraction physical layer complexities physical link control invisible llc upper layers network stack thus llc sublayer higher layers may used mac turn medium access control block formally connected phy via media-independent interface although mac block today typically integrated phy within device package historically mac could used phy independent transmission medium sending data another device network mac sublayer encapsulates higher-level frames frames appropriate transmission medium i.e mac adds syncword preamble also padding necessary adds frame check sequence identify transmission errors forwards data physical layer soon appropriate channel access method permits topologies collision domain bus ring mesh point-to-multipoint topologies controlling data sent wait necessary avoid collisions additionally mac also responsible compensating collisions initiating retransmission jam signal detected receiving data physical layer mac block ensures data integrity verifying sender frame check sequences strips sender preamble padding passing data higher layers according ieee std 802-2001 section 6.2.3 mac sublayer primary functions performed mac layer case ethernet according 802.3-2002 section 4.1.4 functions required mac local network addresses used ieee 802 networks fddi networks called media access control addresses based addressing scheme used early ethernet implementations mac address intended unique serial number mac addresses typically assigned network interface hardware time manufacture significant part address identifies manufacturer assigns remainder address thus provide potentially unique address makes possible frames delivered network link interconnects hosts combination repeaters hubs bridges switches network layer routers thus example ip packet reaches destination sub network destination ip address layer 3 network layer concept resolved address resolution protocol ipv4 neighbor discovery protocol ipv6 mac address layer 2 concept destination host examples physical networks ethernet networks wi-fi networks ieee 802 networks use ieee 802 48-bit mac addresses mac layer required full-duplex point-to-point communication address fields included point-to-point protocols compatibility reasons channel access control mechanisms provided mac layer also known multiple access protocol makes possible several stations connected physical medium share examples shared physical media bus networks ring networks hub networks wireless networks half-duplex point-to-point links multiple access protocol may detect avoid data packet collisions packet mode contention based channel access method used reserve resources establish logical channel circuit-switched channelization-based channel access method used channel access control mechanism relies physical layer multiplex scheme widespread multiple access protocol contention based csma/cd protocol used ethernet networks mechanism utilized within network collision domain example ethernet bus network hub-based star topology network ethernet network may divided several collision domains interconnected bridges switches multiple access protocol required switched full-duplex network today switched ethernet networks often available equipment compatibility reasons use directional antennas millimeter-wave communication wireless personal area network increases probability concurrent scheduling non‐interfering transmissions localized area results immense increase network throughput however optimum scheduling concurrent transmission np-hard problem cellular networks gsm umts lte networks also use mac layer mac protocol cellular networks designed maximize utilization expensive licensed spectrum air interface cellular network layers 1 2 osi model layer 2 divided multiple protocol layers umts lte protocols packet data convergence protocol pdcp radio link control rlc protocol mac protocol base station absolute control air interface schedules downlink access well uplink access devices mac protocol specified 3gpp ts 25.321 umts ts 36.321 lte ts 38.321 5g new radio nr
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Internet protocols
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asynchrony computer programming asynchrony computer programming refers occurrence events independent main program flow ways deal events may outside events arrival signals actions instigated program take place concurrently program execution without program blocking wait results asynchronous input/output example latter cause asynchrony lets programs issue commands storage network devices service requests processor continues executing program provides degree parallelism common way dealing asynchrony programming interface provide subroutines methods functions return caller object sometimes called future promise represents ongoing events object typically come synchronizing operation blocks operation completed programming languages cilk special syntax expressing asynchronous procedure call examples asynchrony include following
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Distributed computing architecture
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european middleware initiative european middleware initiative emi computer software platform high performance distributed computing developed distributed directly emi project base grid middleware distributions used scientific research communities distributed computing infrastructures world especially europe south america asia emi supports broad scientific experiments initiatives worldwide lhc computing grid large hadron collider emi middleware cooperation among three general purpose grid platforms advanced resource connector glite unicore dcache storage software purpose emi distribution consolidate harmonize support original software platforms evolve extend redundant duplicate services resulting merging deprecated favour new services added satisfy user requirements specific consolidation needs standardizing developing common interfaces include adoption common structure accounting resource information exchange authentication authorization input development activities taken users infrastructures projects standardization initiatives changing technological innovations software products adapted necessary comply standard open-source guidelines facilitate integration mainstream operating system distributions cooperation futuregrid us distributed testbed clouds grids high-performance computing announced december 2011 january 2012 emi project formalized partnership imarine project create open data e-infrastructure fisheries management marine conservation 2008 emi software distribution provided middleware components support execution completion millions computational jobs handled 350 centers european grid infrastructure tens petabytes data transfers occurring storage systems centers emi middleware used wlcg infrastructure supports example search higgs boson god particle new types matter searches physicists lhc together research astronomy biology computational chemistry sciences common emi license though licenses used emi open-source product long history behind license apache bsd dcache products released dcache software license adopted affero general public license 1 january 2012 emi products components release grouped four categories areas computing data security infrastructure first release software composed 56 products packaged scientific linux 5 32 64bit second release also made 56 products available scientific linux 5 64bit scientific linux 6 64bit subset services also available debian 6 64bit planned updates third final release contains 61 products scientific linux 5 64bit 480 packages scientific linux 6 64bit 474 packages debian 6 233 packages linux distributions components supported scientific linux platforms debian emi releases two types major releases include components component releases related single product collection components may released update major release major releases delivered per year three planned major releases named european mountains full support updates released address issues code new features provided lasts 12 months standard updates updates released address issues code new features provided lasts 6 months security updates support updates targeting security vulnerabilities provided 6 months older versions emi products superseded newer versions end-of-life announcement made coincides end security updates support period may 2013 24 updates released emi 1 kebnekaise 13 emi 2 matterhorn 3 emi 3 monte bianco minor releases contain interface functional changes backwards-compatible current major release issued times per year revision releases available every week two weeks contain bug fixes emergency releases contain specific bug fixes typically security-related available need using emergency release procedures
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Distributed computing architecture
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uk educational evidence portal uk educational evidence portal eep online resource providing easy access published research evidence-based guidance across areas education related aspects children ’ services developed collaboration organisations make research evidence widely available range audiences including educational professionals practitioners policy makers research community portal went live september 2007 funded number organisations including cfbt education trust dcsf bis tda becta national college hosted eppi-centre institute education university london managed development group meets approximately bi-monthly subset group meets editorial group manages content portal cfbt education trust provides overall leadership portal cited useful information resource various academic government sources uk elsewhere eep searched following ways eep currently developing next release portal improve search results new experienced users subject list browsing database authors names british education thesaurus terms clickable related documents database linked new text mining tool provide automatic subject tags fly database website search
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Databases
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if-map interface metadata access points if-map open specification client/server protocol developed trusted computing group tcg one core protocols trusted network connect tnc open architecture if-map provides common interface metadata access point map database server acting clearinghouse information security events objects elements tnc architecture if-map protocol defines publish/subscribe/search mechanism set identifiers data types if-map protocol first published tcg april 28 2008 originally if-map specification developed support data sharing across various vendor ’ devices applications network security specification also adopted additional use cases data-sharing including physical security 2.0 version if-map spec separated base protocol metadata definitions define different types information represented goal separating base protocol metadata definitions within specification allow specification adopted across technologies cloud computing industrial control systems smart grid leverage existing data models within map framework version 2.1 if-map spec published may 7 2012 primary new feature if-map 2.1 if-map identifier space became extensible reference implementation available gplv3 license google code repository if-map supported variety vendors
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Computer security
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code red computer worm code red computer worm observed internet july 15 2001 attacked computers running microsoft iis web server code red worm first discovered researched eeye digital security employees marc maiffret ryan permeh exploited vulnerability discovered riley hassell named code red code red mountain dew drinking time although worm released july 13 largest group infected computers seen july 19 2001 day number infected hosts reached 359,000 worm showed vulnerability growing software distributed iis described microsoft security bulletin ms01-033 patch available month earlier worm spread using common type vulnerability known buffer overflow using long string repeated letter n overflow buffer allowing worm execute arbitrary code infect machine worm kenneth d. eichman first discover block invited white house discovery payload worm included scanning vulnerable machines worm test see server running remote machine running vulnerable version iis even see running iis apache access logs time frequently entries worm payload string following last n due buffer overflow vulnerable host interprets string computer instructions propagating worm august 4 2001 code red ii appeared although used injection vector completely different payload pseudo-randomly chose targets different subnets infected machines according fixed probability distribution favoring targets subnet often additionally used pattern repeating x characters instead n characters overflow buffer eeye believed worm originated makati city philippines origin vbs/loveletter aka iloveyou worm
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Computer security
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