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cgol cgol pronounced see goll alternative syntax featuring extensible algebraic notation lisp programming language designed maclisp vaughan pratt subsequently ported common lisp notation cgol traditional algebraic notation sometimes called infix notation style algol rather lisp traditional uniformly-parenthesized prefix notation syntax cgol parser based pratt design top-down operator precedence parsing sometimes informally referred pratt parser semantically cgol essentially common lisp additional reader printer support special notations available many commonly used common lisp operations example one write matrix multiply routine cgol infix codice_1 operation referring common lisp codice_2 function infix codice_3 operation referring common lisp codice_4 function preceding example corresponds text native common lisp cgol uses codice_5 read set properties preceding example corresponds text native common lisp illustrates cgol notates function two arguments preceding example corresponds text native common lisp syntax cgol data-driven modifiable extensible cgol known work armed bear common lisp cgol source code text files containing discussions available freeware carnegie-mellon university artificial intelligence repository well richard fateman homepage university california berkeley
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Programming language topics
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dangling pointer dangling pointers wild pointers computer programming pointers point valid object appropriate type special cases memory safety violations generally dangling references wild references references resolve valid destination include phenomena link rot internet dangling pointers arise object destruction object incoming reference deleted deallocated without modifying value pointer pointer still points memory location deallocated memory system may reallocate previously freed memory program dereferences dangling pointer unpredictable behavior may result memory may contain completely different data program writes memory referenced dangling pointer silent corruption unrelated data may result leading subtle bugs extremely difficult find memory reallocated another process attempting dereference dangling pointer cause segmentation faults unix linux general protection faults windows program sufficient privileges allow overwrite bookkeeping data used kernel memory allocator corruption cause system instabilities object-oriented languages garbage collection dangling references prevented destroying objects unreachable meaning incoming pointers ensured either tracing reference counting however finalizer may create new references object requiring object resurrection prevent dangling reference wild pointers arise pointer used prior initialization known state possible programming languages show erratic behavior dangling pointers though less likely stay undetected many compilers raise warning compile time declared variables accessed initialized many languages e.g. c programming language deleting object memory explicitly destroying stack frame return alter associated pointers pointer still points location memory even though may used purposes straightforward example shown operating system able detect run-time references null pointers solution assign 0 null dp immediately inner block exited another solution would somehow guarantee dp used without initialization another frequent source dangling pointers jumbled combination malloc free library calls pointer becomes dangling block memory points freed previous example one way avoid make sure reset pointer null freeing reference—as demonstrated common misstep returning addresses stack-allocated local variable called function returns space variables gets deallocated technically garbage values attempts read pointer may still return correct value 1234 calling func functions called thereafter may overwrite stack storage allocated num values pointer would longer work correctly pointer num must returned num must scope beyond function—it might declared static 1945-1996 created complete object management system free dangling reference phenomenon see consequently note cost kill constant formula_2 similar approach proposed fisher leblanc name locks-and-keys wild pointers created omitting necessary initialization prior first use thus strictly speaking every pointer programming languages enforce initialization begins wild pointer often occurs due jumping initialization omitting compilers able warn like buffer-overflow bugs dangling/wild pointer bugs frequently become security holes example pointer used make virtual function call different address possibly pointing exploit code may called due vtable pointer overwritten alternatively pointer used writing memory data structure may corrupted even memory read pointer becomes dangling lead information leaks interesting data put next structure allocated privilege escalation now-invalid memory used security checks dangling pointer used freed without allocating new chunk memory becomes known use free vulnerability example cve-2014-1776 use-after-free vulnerability microsoft internet explorer 6 11 used zero-day attacks advanced persistent threat c simplest technique implement alternative version free alike function guarantees reset pointer however technique clear pointer variables may contain copy pointer alternative version used even guarantee validity empty pointer calling malloc uses masked define directives construct useful macros creating something like metalanguage embedded tool library apart every case programmers using technique use safe versions every instance free would used failing leads problem also solution limited scope single program project properly documented among structured solutions popular technique avoid dangling pointers c++ use smart pointers smart pointer typically uses reference counting reclaim objects techniques include tombstones method locks-and-keys method see paper fisher leblanc another approach use boehm garbage collector conservative garbage collector replaces standard memory allocation functions c c++ garbage collector approach completely eliminates dangling pointer errors disabling frees reclaiming objects garbage collection languages like java dangling pointers occur mechanism explicitly deallocate memory rather garbage collector may deallocate memory object longer reachable references language rust type system extended include also variables lifetimes resource acquisition initialization unless one disables features language dangling pointers caught compile time reported programming errors expose dangling pointer errors one common programming technique set pointers null pointer invalid address storage point released null pointer dereferenced languages program immediately terminate—there potential data corruption unpredictable behavior makes underlying programming mistake easier find resolve technique help multiple copies pointer debuggers automatically overwrite destroy data freed usually specific pattern codice_1 microsoft visual c/c++ debugger example uses codice_2 codice_3 codice_4 depending freed usually prevents data reused making useless also prominent pattern serves show programmer memory already freed tools polyspace totalview valgrind mudflap addresssanitizer tools based llvm also used detect uses dangling pointers tools softbound insure++ checkpointer instrument source code collect track legitimate values pointers metadata check pointer access metadata validity another strategy suspecting small set classes temporarily make member functions virtual class instance destructed/freed pointer virtual method table set codice_5 call member function crash program show guilty code debugger term dangling pointer may also used contexts programming especially technical people example phone number person since changed phones real-world example dangling pointer another example entry online encyclopedia refers another entry whose title changed changing previously existing references entry dangling pointers
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Computer security
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plesiochronous digital hierarchy plesiochronous digital hierarchy pdh technology used telecommunications networks transport large quantities data digital transport equipment fibre optic microwave radio systems term plesiochronous derived greek plēsios meaning near chronos time refers fact pdh networks run state different parts network nearly quite perfectly synchronized backbone transport networks replaced pdh networks synchronous digital hierarchy sdh synchronous optical networking sonet equipment ten years ending around turn millennium 2000 whose floating payloads relaxed stringent timing requirements pdh network technology cost north america 4.5 billion 1998 alone p. 171 pdh allows transmission data streams nominally running rate allowing variation speed around nominal rate analogy two watches nominally running rate clocking 60 seconds every minute however link watches guarantee run exactly rate highly likely one running slightly faster data rate controlled clock equipment generating data rate allowed vary ±50 ppm 2048 kbit/s according itu-t recommendation means different data streams probably run slightly different rates one another order transport multiple data streams one place another common transmission medium multiplexed groups four four data streams necessarily running rate compensation introduced typically multiplexer takes data 4 incoming 2.048 mbit/s data streams feeds 2.112 mbit/s stream via buffer store leaving series fixed gaps frame data rate thus 2.112 mbit/s x number bits frame – number gaps number bits frame slightly greater 2.048 mbit/s 50ppm extra gap added slightly smaller 2.048 mbit/s – 50ppm thus average data rate made exactly equal incoming rate adding gap frames others extra gap fixed place frame referred stuffable bit contain data i.e ’ gap stuffed data 4 data streams contained 4 data streams 2.112 mbit/s synchronous easily multiplexed give single stream 8.448 mbit/s taking 1 bit stream 1 followed 1 bit stream 2 3 4 etc fixed gaps accommodate synchronisation word allows demultiplexer identify start frame others contain control bits stream say whether stuffable bit stuffed i.e contains data process reversed demultiplexer 4 data streams produced exactly bit rate previous timing irregularity ironed using phase locked loop scheme allow addition stuffed bit soon required stuffable bit fixed point frame necessary wait stuffable bit time slot wait results waiting time jitter arbitrarily low frequency i.e zero entirely eliminated filtering effects phase lock loop worst possible stuffing ratio would 1 frame 2 gives theoretical 0.5 bit jitter stuffing ratio carefully chosen give theoretical minimum jitter practical system however actual decision stuff may made comparing read address write address input buffer store position frame decision made varies adds second variable dependent length store process sometimes called pulse justification justification printing adding gaps line takes full column width believed term preferred ... stuffing stuffable bits waiting time jitter jitter get waiting stuff stuffable bit though technically correct sound like pleonasm similar techniques used combine four × 8 mbit/s together plus bit stuffing frame alignment giving 34 mbit/s four × 34 mbit/s gives 140 four × 140 gives 565 telecommunications networks independent clocks free-running precision clocks located nodes used synchronization variable storage buffers installed accommodate variations transmission delay nodes made large enough accommodate small time phase departures among nodal clocks control transmission traffic may occasionally interrupted allow buffers emptied stored data
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Internet protocols
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extended backus–naur form computer science extended backus-naur form ebnf family metasyntax notations used express context-free grammar ebnf used make formal description formal language computer programming language extensions basic backus–naur form bnf metasyntax notation earliest ebnf developed niklaus wirth incorporating concepts different syntax notation wirth syntax notation however many variants ebnf use international organization standardization adopted ebnf standard iso/iec 14977 1996 however according zaytsev standard ended adding yet another three dialects chaos noting lack success also notes iso ebnf even used iso standards wheeler argues using iso standard using ebnf recommends considering alternative ebnf notations one w3c extensible markup language xml 1.0 fifth edition article uses ebnf specified iso examples applying ebnfs ebnf variants use somewhat different syntactic conventions ebnf code expresses grammar formal language ebnf consists terminal symbols non-terminal production rules restrictions governing terminal symbols combined legal sequence examples terminal symbols include alphanumeric characters punctuation marks whitespace characters ebnf defines production rules sequences symbols respectively assigned nonterminal digit excluding zero 1 2 3 4 5 6 7 8 9 digit 0 digit excluding zero production rule defines nonterminal digit left side assignment vertical bar represents alternative terminal symbols enclosed quotation marks followed semicolon terminating character hence digit 0 digit excluding zero 1 2 3 forth 9 production rule also include sequence terminals nonterminals separated comma twelve 1 2 two hundred one 2 0 1 three hundred twelve 3 twelve twelve thousand two hundred one twelve two hundred one expressions may omitted repeated represented curly braces ... natural number digit excluding zero digit case strings 1 2 ... 10 ... 12345 ... correct expressions represent everything set within curly braces may repeated arbitrarily often including option represented squared brackets ... everything set within square brackets may present integer 0 natural number therefore integer zero 0 natural number may preceded optional minus sign ebnf also provides among things syntax describe repetitions specified number times exclude part production insert comments ebnf grammar following represents proposed iso/iec 14977 standard r. s. scowen page 7 table 1 even ebnf described using ebnf consider sketched grammar letter b c e f g digit 0 1 2 3 4 5 6 7 8 9 symbol character letter digit symbol identifier letter letter digit terminal character character lhs identifier rhs identifier rule lhs rhs grammar rule pascal-like programming language allows assignments defined ebnf follows syntactically correct program would language easily extended control flows arithmetical expressions input/output instructions small usable programming language would developed grammar defined ebnf also represented bnf though representations latter generally lengthier e.g. options repetitions directly expressed bnf require use intermediate rule alternative production defined either nothing optional production option either repeated production recursively repetition constructs still used ebnf bnf uses symbols := include quotes around terminal strings prevents characters used languages requires special symbol empty string ebnf terminals strictly enclosed within quotation marks ... ... angle brackets ... nonterminals omitted bnf syntax represent rule one line whereas ebnf terminating character semicolon marks end rule furthermore ebnf includes mechanisms enhancements defining number repetitions excluding alternatives comments etc examples following syntax rules illustrate facilities expressing repetition aa bb 3 aa b cc 3 aa c dd aa ee aa aa e ff 3 aa 3 aa f gg 3 aa g terminal strings defined rules follows according iso 14977 standard ebnf meant extensible two facilities mentioned first part ebnf grammar special sequence arbitrary text enclosed question marks interpretation text inside special sequence beyond scope ebnf standard example space character could defined following rule second facility extension using fact parentheses ebnf placed next identifiers must concatenated following valid ebnf following valid ebnf therefore extension ebnf could use notation example lisp grammar function application could defined following rule
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Programming language topics
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boris loza boris loza may 5 1960 founder safepatrol solutions tego systems well certified information systems security professional cissp born krasnodar russia attained masters degree age 22 phd age 26 computer science cybernetics still living former ussr loza published 30 scientific articles well secured one patent upon relocating canada 1996 phd confirmed higher attestation committee university toronto since immigrating loza worked ibm global services senior system administrator fidelity investments principal information systems security specialist loza interest computer security led continue developing products well publish articles book articles featured hacker magazines original phrack contributed 40 articles us industry magazines usenix sysadmin inside solaris inside internet several others 2005 loza published computer security book titled unix solaris linux practical security cookbook securing unix operating systems without third-party application number loza articles featured press including sun microsystems novell linux bsd communities work russian english translated several languages including french bulgarian polish loza holds secret level clearance government canada acts subject matter expert courts filed several information security patents usa conducted hundreds information security assessments security forensics penetration tests white hacking assessments speaker author trainer loza worked consults fortune global 500 companies including ibm fidelity investments well government agencies start-ups work cited books hack proofing sun solaris 8 among others 2008 boris loza internationally recognized work contribution field computer security awareness winner first international cyber security awareness contest held isc ² computer security products developed boris loza well co-authors loza current project notebak—a computer security system used personal corporate systems
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Computer security
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svi-838 svi-838 also known x'press 16 last microcomputer produced spectravideo hong kong although pc clone standard sound video coprocessors msx2 making hybrid system sales unimpressive considered collectible svi-811 adapter machine could run msx1 programs cartridge main itens
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Computer architecture
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firebase firebase mobile web application development platform developed firebase inc. 2011 acquired google 2014 october 2018 firebase platform 18 products used 1.5 million apps firebase evolved envolve prior startup founded james tamplin andrew lee 2011 envolve provided developers api enables integration online chat functionality websites releasing chat service tamplin lee found used pass application data n't chat messages developers using envolve sync application data game state real time across users tamplin lee decided separate chat system real-time architecture powered founded firebase separate company september 2011 launched public april 2012 firebase first product firebase real-time database api synchronizes application data across ios android web devices stores firebase cloud product assists software developers building real-time collaborative applications may 2012 one month beta launch firebase raised 1.1m seed funding venture capitalists flybridge capital partners greylock partners founder collective new enterprise associates june 2013 company raised 5.6m series funding venture capitalists union square ventures flybridge capital partners 2014 firebase launched two products firebase hosting firebase authentication positioned company mobile backend service october 2014 firebase acquired google october 2015 google acquired divshot merge firebase team may 2016 google i/o company annual developer conference firebase expanded services become unified platform mobile developers firebase integrates various google services including google cloud platform admob google ads offer broader products scale developers google cloud messaging google service send push notifications android devices superseded firebase product firebase cloud messaging added functionality deliver push notifications ios web devices january 2017 google acquired fabric crashlytics twitter add services firebase october 2017 firebase launched cloud firestore realtime document database successor product original firebase realtime database firebase analytics cost-free app measurement solution provides insight app usage user engagement formerly known google cloud messaging gcm firebase cloud messaging fcm cross-platform solution messages notifications android ios web applications 2016 used cost firebase auth service authenticate users using client-side code supports social login providers facebook github twitter google google play games additionally includes user management system whereby developers enable user authentication email password login stored firebase firebase provides realtime database backend service service provides application developers api allows application data synchronized across clients stored firebase cloud company provides client libraries enable integration android ios javascript java objective-c swift node.js applications database also accessible rest api bindings several javascript frameworks angularjs react ember.js backbone.js rest api uses server-sent events protocol api creating http connections receiving push notifications server developers using realtime database secure data using company server-side-enforced security rules january 31st 2019 cloud firestore officially brought beta making official product firebase line-up successor firebase original databasing system real-time database allows nested documents fields rather tree-view provided real-time database firebase storage provides secure file uploads downloads firebase apps regardless network quality developer use store images audio video user-generated content firebase storage backed google cloud storage firebase hosting static dynamic web hosting service launched may 13 2014 supports hosting static files css html javascript files well support cloud functions service delivers files content delivery network cdn http secure https secure sockets layer encryption ssl firebase partners fastly cdn provide cdn backing firebase hosting company states firebase hosting grew customer requests developers using firebase real-time database needed place host content ml kit mobile machine learning system developers launched may 8 2018 beta google i/o 2018 ml kit api feature variety features including text recognition detecting faces scanning barcodes labelling images recognising landmarks currently available ios android developers may also import tensorflow lite models given api n't enough api used on-device cloud crash reporting creates detailed reports errors app errors grouped clusters similar stack traces triaged severity impact app users addition automatic reports developer log custom events help capture steps leading crash acquiring crashlytics firebase using firebase crash reporting firebase performance provides insights app performance latencies app users experience firebase test lab android ios provides cloud-based infrastructure testing android ios apps one operation developers initiate testing apps across wide variety devices device configurations test results—including logs videos screenshots—are made available project firebase console even developer n't written test code app test lab exercise app automatically looking crashes.test lab ios currently beta earn google admob app marketing scope admob google product integrates firebase audience dynamic firebase links smart urls dynamically change behavior provide best available experience across multiple platforms desktop web browsers well ios android in-depth links mobile app dynamic links work app installs user opens dynamic link ios android application installed user prompted install app first installed application start running access link
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Distributed computing architecture
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growl software growl global notification system pop-up notification implementation mac os x windows operating systems applications use growl display small notifications events may important user software allows users fully control notifications allowing application developers spend less time creating notifications growl developers concentrate usability notifications growl used conjunction apple notification center included mac os x 10.8 mountain lion higher growl installed preference pane added mac os x system preferences pane may used enable disable growl notifications specific applications specific notifications application notification provides information download finished name current itunes track software comes multiple display plugins providing user different style options presenting notifications display plugins include visual styles well ability send notifications via email sms push notifications additional third-party plugins scripts exist add growl notifications ichat mail thunderbird safari itunes application developers may make use growl api send notifications users growl includes bindings developers use objective-c c perl python tcl applescript java ruby programming languages growl website lists applications install growl without user permission including adobe creative suite 5 adobe published blog post apologizing installing growl users systems without permission says actively working mitigate problem adobe article knowledge base explaining notifications cs5 sends remove growl
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Internet protocols
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identity-based security identity-based security approach control access digital product service based authenticated identity individual allows organizations grant access specific users access variety digital services using credentials ensuring accurate match users entitled actually receive also permitting access constraints company device location application type attributes underpinning identity-based security approach identity-based access control ibac identity-based licensing concept nist defines identity-based security policies policies based identities and/or attributes object system resource accessed subject user group users process device requesting access advantages identity-based security approach include ability exercise fine-grained control allowed use services functions users perform device-agnostic offering possibility enforce access control policy across variety devices smartphones tablets pcs identity-based security network security approach put forward cyberoam includes security components provides visibility control user activity particular network offers network security system includes user human identity part firewall rule matching criteria concept includes treating user identity eighth layer also known human layer network protocol stack thus attaching user identity security authenticating authorizing auditing network takes different step conventional security appliances bind security ip-addresses approach allows organisations create security policies align users groups rather ip addresses ultimately gives precise control access network—and access identity-based security prevents systems address spoofing attacks combining point encryption authentication access control single unit
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Computer security
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toc protocol toc protocol talk oscar protocol protocol used third-party aol instant messenger clients several clients aol produced sometime near august 19 2005 aol discontinued support protocol longer uses instant messaging clients actively maintains windows mac clients aol instant messenger icq systems however produce several toc clients including tik tac written tcl/tk tnt written emacs lisp open source java client originally called tic later became quick buddy web applet aol also provided toc protocol specification openly developers hopes use instead proprietary oscar protocol use july 2012 aol turned toc2 servers longer possible connect aim using protocol toc ascii-based protocol oscar binary protocol addition toc contained fewer features oscar counterpart oscar provides functionality buddy icons file transfer advertising toc acted wrapper oscar protocol grand scheme things toc server nothing oscar client happened listen socket translating messages two protocols upon login toc client specified oscar login server presumably either login.oscar.aol.com login.icq.com toc server used behalf client toc used flap encapsulate messages oscar however flap hacked way implemented port http server default toc server operated http mode indistinguishable typical web server connecting client place http request writes string flapon followed two crlfs toc would switch gears start reading flap messages upon getting user profile client expected re-connect toc use http server would host user profile html connected two basic message formats communications inside flap existed client-to-server messages sent format resembling unix-style command line commands whitespace-separated arguments quoting backslash escape sequences server-to-client messages much simpler sent colon-separated ascii strings manner similar many unix config files thus quite easy write client incoming messages easy parse outgoing commands easy generate contrast oscar due binary representation data difficult understand toc2 protocol updated version toc protocol talk oscar protocol existence never documented aol used aol instant messenger clients clients beginning offer plugins toc2 light aol recent shutdown toc servers like predecessor toc2 ascii protocol lacks features oscar unlike toc toc2 known support buddy icons receiving file transfers sending toc2 operates essentially way toc wrapper oscar porting code toc toc2 remarkably easy well similarities toc1.0 toc2.0 better defined differences
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Internet protocols
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pop-11 pop-11 reflective incrementally compiled programming language many features interpreted language core language poplog programming environment developed originally university sussex recently school computer science university birmingham hosts poplog website pop-11 evolution language pop-2 developed edinburgh university features open stack model like forth among others mainly procedural supports declarative language constructs including pattern matcher mostly used research teaching artificial intelligence although features sufficient many classes problems often used introduce symbolic programming techniques programmers conventional languages like pascal find pop syntax familiar lisp one pop-11 features supports first-class functions pop-11 core language poplog system availability compiler compiler subroutines run-time requirement incremental compilation gives ability support far wider range extensions would possible using macro facility made possible incremental compilers added prolog common lisp standard ml could added required support either mixed language development development second language without using pop-11 constructs made possible poplog used teachers researchers developers interested one languages successful product developed pop-11 clementine data-mining system developed isl spss bought isl decided port clementine c++ java eventually succeeded great effort perhaps loss flexibility provided use ai language pop-11 time available part expensive commercial package poplog since 1999 freely available part open source version poplog including various additional packages teaching libraries online version eliza using pop-11 available birmingham university sussex david young used pop-11 combination c fortran develop suite teaching interactive development tools image processing vision made available popvision extension poplog example simple pop-11 program prints one includes list processing examples using pop-11 pattern matcher makes relatively easy students learn develop sophisticated list-processing programs without treat patterns tree structures accessed 'head 'tail functions car cdr lisp found online introductory tutorial matcher heart simagent sim_agent toolkit powerful features toolkit linking pattern variables inline code variables would difficult implement without incremental compiler facilities category lisp programming language family category artificial intelligence category history computing united kingdom category science technology east sussex category university sussex
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Programming language topics
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history microsoft sql server history microsoft sql server begins first microsoft sql server product sql server 1.0 16-bit server os/2 operating system 1989 extends current day june 12th 1988 microsoft joined ashton-tate sybase create variant sybase sql server ibm os/2 developed jointly microsoft released following year first version microsoft sql server served microsoft entry enterprise-level database market competing oracle ibm later sybase sql server 4.2 shipped 1992 bundled os/2 version 1.3 followed version 4.21 windows nt released alongside windows nt 3.1 sql server 6.0 first version designed nt include direction sybase time windows nt released july 1993 sybase microsoft parted ways pursued design marketing schemes microsoft negotiated exclusive rights versions sql server written microsoft operating systems 1996 sybase changed name product adaptive server enterprise avoid confusion microsoft sql server 1994 microsoft sql server carried three sybase copyright notices indication origin sql server 7.0 major rewrite c++ older sybase engine coded c. data pages enlarged 2k bytes 8k bytes extents thereby grew 16k bytes 64k bytes user mode scheduling ums introduced handle sql server threads better windows preemptive multi-threading also adding support fibers lightweight threads introduced nt 4.0 used avoid context switching sql server 7.0 also introduced multi-dimensional database product called sql olap services became analysis services sql server 2000 sql server 7.0 would last version run dec alpha platform although pre-release versions sql 2000 well windows 2000 compiled alpha canceled never commercially released sql server 2000 included modifications extensions sybase code base adding support ia-64 architecture mainstream support sql server 2005 legacy sybase code completely rewritten since release sql server 2000 advances made performance client ide tools several complementary systems packaged sql server 2005 include sql server 2000 also introduced many t-sql language enhancements table variables user-defined functions indexed views instead triggers cascading referential constraints basic xml support release service pack 3 microsoft also released first 64-bit version sql server itanium ia-64 platform confused x86-64 platform sql server relational engine sql agent ported itanium time client tools enterprise manager would still need run 32-bit x86 clients first release sql ia-64 version 8.00.760 build date february 6 2003 sql server 2005 formerly codenamed yukon released november 2005 included native support managing xml data addition relational data purpose defined codice_1 data type could used either data type database columns literals queries xml columns associated xsd schemas xml data stored verified schema xml converted internal binary data type stored database specialized indexing methods made available xml data xml data queried using xquery sql server 2005 added extensions t-sql language allow embedding xquery queries t-sql also defines new extension xquery called xml dml allows query-based modifications xml data sql server 2005 also allows database server exposed web services using tabular data stream tds packets encapsulated within soap protocol requests data accessed web services results returned xml common language runtime clr integration introduced version enabling one write sql code managed code clr relational data t-sql augmented error handling features try/catch support recursive queries ctes common table expressions sql server 2005 also enhanced new indexing algorithms syntax better error recovery systems data pages checksummed better error resiliency optimistic concurrency support added better performance permissions access control made granular query processor handles concurrent execution queries efficient way partitions tables indexes supported natively scaling database onto cluster easier sql clr introduced sql server 2005 let integrate .net framework sql server 2005 introduced multi-version concurrency control mvcc user facing features include new transaction isolation level called snapshot variation read committed isolation level based statement-level data snapshots sql server 2005 introduced mars multiple active results sets method allowing usage database connections multiple purposes sql server 2005 introduced dmvs dynamic management views specialized views functions return server state information used monitor health server instance diagnose problems tune performance sql server 2005 first version native support x64 platform service pack 1 sp1 sql server 2005 introduced database mirroring high availability option provides redundancy failover capabilities database level failover performed manually configured automatic failover automatic failover requires witness partner operating mode synchronous also known high-safety full safety database mirroring included first release sql server 2005 evaluation purposes prior sp1 enabled default supported microsoft extended support sql server 2005 ended april 12 2016 sql server 2008 formerly codenamed katmai released august 6 2008 announced sql server special interest group esri 2008 user conference august 6 2008 ed katibah spatial program manager microsoft aims make data management self-tuning self organizing self maintaining development sql server always technologies provide near-zero downtime sql server 2008 also includes support structured semi-structured data including digital media formats pictures audio video multimedia data current versions multimedia data stored blobs binary large objects generic bitstreams intrinsic awareness multimedia data allow specialized functions performed according paul flessner senior vice president server applications microsoft sql server 2008 data storage backend different varieties data xml email time/calendar file document spatial etc well perform search query analysis sharing synchronization across data types new data types include specialized date time types spatial data type location-dependent data better support unstructured semi-structured data provided using new filestream data type used reference file stored file system structured data metadata file stored sql server database whereas unstructured component stored file system files accessed via win32 file handling apis well via sql server using t-sql latter accesses file data blob backing restoring database backs restores referenced files well sql server 2008 also natively supports hierarchical data includes t-sql constructs directly deal without using recursive queries full-text search functionality integrated database engine according microsoft technical article simplifies management improves performance spatial data stored two types flat earth geometry planar data type represents geospatial data projected native spherical coordinate system plane round earth data type geography uses ellipsoidal model earth defined single continuous entity suffer singularities international dateline poles map projection zone edges approximately 70 methods available represent spatial operations open geospatial consortium simple features sql version 1.1 sql server includes better compression features also helps improving scalability enhanced indexing algorithms introduced notion filtered indexes also includes resource governor allows reserving resources certain users workflows also includes capabilities transparent encryption data tde well compression backups sql server 2008 supports ado.net entity framework reporting tools replication data definition built around entity data model sql server reporting services gain charting capabilities integration data visualization products dundas data visualization inc. acquired microsoft management side sql server 2008 includes declarative management framework allows configuring policies constraints entire database certain tables declaratively version sql server management studio included sql server 2008 supports intellisense sql queries sql server 2008 database engine sql server 2008 also makes databases available via windows powershell providers management functionality available cmdlets server running instances managed windows powershell final sql server 2008 service pack 10.00.6000 service pack 4 released september 30 2014 sql server 2008 r2 10.50.1600.1 formerly codenamed kilimanjaro announced teched 2009 released manufacturing april 21 2010 sql server 2008 r2 adds certain features sql server 2008 including master data management system branded master data services central management master data entities hierarchies also multi server management centralized console manage multiple sql server 2008 instances services including relational databases reporting services analysis services integration services sql server 2008 r2 includes number new services including powerpivot excel sharepoint master data services streaminsight report builder 3.0 reporting services add-in sharepoint data-tier function visual studio enables packaging tiered databases part application sql server utility named uc utility control point part amsm application multi-server management used manage multiple sql servers first sql server 2008 r2 service pack 10.50.2500 service pack 1 released july 11 2011 second sql server 2008 r2 service pack 10.50.4000 service pack 2 released july 26 2012 final sql server 2008 r2 service pack 10.50.6000 service pack 3 released september 26 2014 sql 2008 r2 would last version sql server run itanium ia-64 platform however x64 platform would continue force extended support sql server itanium would continue 2018 2011 professional association sql server pass summit october 11 microsoft announced next major version sql server codenamed denali would sql server 2012 released manufacturing march 6 2012 sql server 2012 service pack 1 released manufacturing november 9 2012 service pack 2 released manufacturing june 10 2014 announced last version natively support ole db instead prefer odbc native connectivity sql server 2012 new features enhancements include always sql server failover cluster instances availability groups provides set options improve database availability contained databases simplify moving databases instances new modified dynamic management views functions programmability enhancements including new spatial features metadata discovery sequence objects throw statement performance enhancements columnstore indexes well improvements online partition level operations security enhancements including provisioning setup new permissions improved role management default schema assignment groups sql server 2014 released manufacturing march 18 2014 released general public april 1 2014 build number 12.0.2000.8 release november 2013 two ctp revisions ctp1 ctp2 sql server 2014 provides new in-memory capability tables fit entirely memory also known hekaton whilst small tables may entirely resident memory versions sql server also may reside disk work involved reserving ram writing evicted pages disk loading new pages disk locking pages ram operated many tasks treating table guaranteed entirely resident memory much 'plumbing disk-based databases avoided disk-based sql server applications also provides ssd buffer pool extension improve performance cache ram spinning media sql server 2014 also enhances always hadr solution increasing readable secondaries count sustaining read operations upon secondary-primary disconnections provides new hybrid disaster recovery backup solutions microsoft azure enabling customers use existing skills on-premises version sql server take advantage microsoft global datacenters addition takes advantage new windows server 2012 windows server 2012 r2 capabilities database application scalability physical virtual environment microsoft provides three versions sql server 2014 downloading one runs microsoft azure sql server 2014 cab sql server 2014 iso sql server 2014 sp1 consisting primarily bugfixes released may 15 2015 sql server 2014 last version available x86/ia32 architecture official general availability ga release date sql server 2016 june 1 2016 rtm version 13.0.1601.5 sql server 2016 supported x64 processors longer supported x86 processors microsoft sql server 2017 recent version available microsoft launched sql server 2017 october 2nd 2017 along support linux
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Databases
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tribe flood network tribe flood network tfn set computer programs conduct various ddos attacks icmp flood syn flood udp flood smurf attack first tfn initiated attacks described cert incident note 99-04 tfn2k written mixter security professional hacker based germany
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Computer security
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relying party relying party rp computer term used refer server providing access secure software application claims-based applications claim statement entity makes order establish access also called relying party rp applications rps also called “ claims aware applications ” “ claims-based applications ” web applications services rps security token service sts rp redirects clients sts authenticates client issues security token containing set claims client identity present rp instead application authenticating user directly rp extract claims token use identity related tasks openid standard defines situation whereby cooperating site act rp allowing user log multiple sites using one set credentials user benefits share login credentials multiple sites operators cooperating site avoid develop login mechanism application demonstrating concept relying party software running mobile devices used granting user access software applications also secure building access without user enter credentials time
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Computer security
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multiplexer electronics multiplexer mux device selects several analog digital input signals forwards single output line multiplexer formula_1 inputs formula_2 select lines used select input line send output multiplexers mainly used increase amount data sent network within certain amount time bandwidth multiplexer also called data selector multiplexers also used implement boolean functions multiple variables electronic multiplexer makes possible several signals share one device resource example one a/d converter one communication line instead one device per input signal conversely demultiplexer demux device taking single input selecting signals output compatible mux connected single input shared selection line multiplexer often used complementary demultiplexer receiving end electronic multiplexer considered multiple-input single-output switch demultiplexer single-input multiple-output switch schematic symbol multiplexer isosceles trapezoid longer parallel side containing input pins short parallel side containing output pin schematic right shows 2-to-1 multiplexer left equivalent switch right formula_3 wire connects desired input output one use multiplexers economizing connections single channel connecting multiplexer single output demultiplexer single input image right demonstrates benefit case cost implementing separate channels data source higher cost inconvenience providing multiplexing/demultiplexing functions receiving end data link complementary demultiplexer usually required break single data stream back original streams cases far end system may functionality greater simple demultiplexer demultiplexing still occurs technically may never implemented discretely would typical multiplexer serves number ip network users feeds directly router immediately reads content entire link routing processor demultiplexing memory converted directly ip sections often multiplexer demultiplexer combined together single piece equipment conveniently referred multiplexer circuit elements needed ends transmission link communications systems transmit directions analog circuit design multiplexer special type analog switch connects one signal selected several inputs single output digital circuit design selector wires digital value case 2-to-1 multiplexer logic value 0 would connect formula_4 output logic value 1 would connect formula_5 output larger multiplexers number selector pins equal formula_6 formula_7 number inputs example 9 16 inputs would require fewer 4 selector pins 17 32 inputs would require fewer 5 selector pins binary value expressed selector pins determines selected input pin 2-to-1 multiplexer boolean equation formula_8 formula_9 two inputs formula_10 selector input formula_11 output expressed truth table simpler notation tables show formula_13 formula_14 formula_15 formula_16 straightforward realization 2-to-1 multiplexer would need 2 gates gate gate mathematically correct direct physical implementation would prone race conditions require additional gates suppress larger multiplexers also common stated require formula_6 selector pins formula_2 inputs common sizes 4-to-1 8-to-1 16-to-1 since digital logic uses binary values powers 2 used 4 8 16 maximally control number inputs given number selector inputs boolean equation 4-to-1 multiplexer following 4-to-1 multiplexer constructed 3-state buffers gates gates acting decoder subscripts formula_20 inputs indicate decimal value binary control inputs input let larger multiplexers constructed using smaller multiplexers chaining together example 8-to-1 multiplexer made two 4-to-1 one 2-to-1 multiplexers two 4-to-1 multiplexer outputs fed 2-to-1 selector pins 4-to-1 put parallel giving total number selector inputs 3 equivalent 8-to-1 7400 series several ics contain multiplexer demultiplexers take one data input number selection inputs several outputs forward data input one outputs depending values selection inputs demultiplexers sometimes convenient designing general purpose logic demultiplexer input always true demultiplexer acts decoder means function selection bits constructed logically or-ing correct set outputs x input selector b outputs formula_21 formula_22 7400 series several ics contain demultiplexer multiplexers also used programmable logic devices specifically implement boolean functions boolean function n variables one result implemented multiplexer n selector inputs variables connected selector inputs function result 0 1 possible combination selector inputs connected corresponding data input especially useful situations cost factor modularity ease modification one variables example also available inverted multiplexer n -1 selector inputs sufficient data inputs connected 0 1 according desired output combination selector inputs
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Internet protocols
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zeropc zeropc commercial webtop developed zerodesktop inc. located san mateo california zeropc called personal cloud os mimicked look feel functionality desktop environment real operating system software launched september 2011 disrupt sf 2011 event recently selected finalist sxsw 2012 innovative web technology category zeropc web-based required java applet operate bundled productivity tool thinkfree web applications found zeropc built java back end features included drag-and-drop functionality cloud dashboard personal cloud storage meta services zeropc belonged category services intended turn web full-fledged platform using web services foundation along presentation technologies replicated experience desktop applications users zeropc aggregates content users easily access transfer share whatever content want using internet browser anywhere anytime device meta-cloud layer supports dropbox box sugarsync onedrive 4shared google drive evernote picasa flickr instagram facebook twitter photobucket zeropc cloud os platform also provides extensive apis ios android app developers features found zeropc file sharing webmail cloud content navigator instant messenger sticky note audio/video player office productivity applications zeropc 2.0 platform ran aws free paid users platform licensable telco isv commercial purpose clients sfr sk telecom hancom others june 1 2017 zeropc servers switched completely zeropc longer service since parent company ncomputing launched virtual desktop service cloud aws public zeropc web desktop compatible mac os x microsoft windows platforms certified operate safari 6.0 firefox 15.0.1 google chrome 22.0.1229.79 internet explorer 8 9 zeropc front end user interface executes entirely within internet browser see uses html features html5 javascript ajax optional java plug-in communication zeropc front end user interface zeropc back end servers encrypted using ssl https protocol furthermore content stored zeropc server-side repository also encrypted using 256-bit advanced encryption standard aes-256 amazon web services simple storage service s3 zeropc users could connect zeropc profile storage services dropbox box connection allows zeropc user fully manage content stored storage services establish connection zeropc rigorously adhered oauth implementation provided target storage service upon completion oauth process zeropc stores relevant access token user profile token along sensitive password related data encrypted using aes 256-bit key size noted zeropc platform hosted amazon web services infrastructure available general consumer user allowed sign selecting one three account plans including no-cost option zeropc could also white-labeled organizations wishing provide functionality users white-label options include managed hosting amazon web services infrastructure also installation within organization infrastructure zeropc infrastructure provided user access content features several different ways described article user access information signing zeropc web desktop additionally zeropc offers native applications designed run popular mobile devices including smartphones tablets zeropc founded chief executive officer young song entrepreneur previously founded ncomputing 60 million venture-backed company also co-founded emachines inc. low-cost computer brand later acquired gateway
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Distributed computing architecture
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orbital angular momentum multiplexing orbital angular momentum oam multiplexing physical layer method multiplexing signals carried electromagnetic waves using orbital angular momentum electromagnetic waves distinguish different orthogonal signals orbital angular momentum one two forms angular momentum light oam distinct confused light spin angular momentum spin angular momentum light offers two orthogonal quantum states corresponding two states circular polarization demonstrated equivalent combination polarization multiplexing phase shifting oam hand relies extended beam light higher quantum degrees freedom come extension oam multiplexing thus access potentially unbounded set states offer much larger number channels subject constraints real-world optics although oam multiplexing promises significant improvements bandwidth used concert existing modulation multiplexing schemes still experimental technique far demonstrated laboratory following early claim oam exploits new quantum mode information propagation technique become controversial however nowadays understood particular form tightly modulated mimo multiplexing strategy obeying classical information theoretic bounds oam multiplexing demonstrated using light beams free space early 2004 since research oam proceeded two areas radio frequency optical transmission experiment 2011 demonstrated oam multiplexing two incoherent radio signals distance 442 m. claimed oam improve achieved conventional linear-momentum based rf systems already use mimo since theoretical work suggests radio frequencies conventional mimo techniques shown duplicate many linear-momentum properties oam-carrying radio beam leaving little extra performance gain november 2012 reports disagreement basic theoretical concept oam multiplexing radio frequencies research groups tamburini thide many different camps communications engineers physicists declaring belief oam multiplexing implementation mimo others holding assertion oam multiplexing distinct experimentally confirmed phenomenon 2014 group researchers described implementation communication link 8 millimetre-wave channels multiplexed using combination oam polarization-mode multiplexing achieve aggregate bandwidth 32 gbit/s distance 2.5 metres results agree well predictions severely limited distances made edfors et al industrial interest long-distance microwave oam multiplexing seems diminishing since 2015 original promoters oam-based communication radio frequencies including siae microelettronica published theoretical investigation showing real gain beyond traditional spatial multiplexing terms capacity overall antenna occupation oam multiplexing used optical domain 2012 researchers demonstrated oam-multiplexed optical transmission speeds 2.5 tbits/s using 8 distinct oam channels single beam light short free-space path roughly one metre work ongoing applying oam techniques long-range practical free-space optical communication links oam multiplexing implemented existing long-haul optical fiber systems since systems based single-mode fibers inherently support oam states light instead few-mode multi-mode fibers need used additional problem oam multiplexing implementation caused mode coupling present conventional fibers cause changes spin angular momentum modes normal conditions changes orbital angular momentum fibers bent stressed mode instability direct-detection oam multiplexing yet realized long-haul communications 2012 transmission oam states 97 purity 20 meters special fibers demonstrated researchers boston university later experiments shown stable propagation modes distances 50 meters improvements distance subject ongoing work ongoing research making oam multiplexing work future fibre-optic transmission systems includes possibility using similar techniques used compensate mode rotation optical polarization multiplexing alternative direct-detection oam multiplexing computationally complex coherent-detection mimo digital signal processing dsp approach used achieve long-haul communication strong mode coupling suggested beneficial coherent-detection-based systems paper bozinovic et al published science 2013 claims successful demonstration oam-multiplexed fiber-optic transmission system 1.1 km test path test system capable using 4 different oam channels simultaneously using fiber vortex refractive-index profile also demonstrated combined oam wdm using apparatus using two oam modes 2014 articles g. milione et al h. huang et al claimed first successful demonstration oam-multiplexed fiber-optic transmission system 5 km conventional optical fiber i.e. optical fiber circular core graded index profile contrast work bozinovic et al. used custom optical fiber vortex refractive-index profile work g. milione et al h. huang et al showed oam multiplexing could used commercially available optical fibers using digital mimo post-processing correct mode mixing within fiber method sensitive changes system change mixing modes propagation changes bending fiber requires substantial computation resources scale larger numbers independent modes shows great promise 2018 zengji yue haoran ren shibiao wei jiao lin min gu royal melbourne institute technology miniaturised technology shrinking size large dinner table small chip could integrated communications networks chip could predict increase capacity fibre-optic cables least 100-fold likely higher technology developed
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Internet protocols
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ransomware ransomware type malware cryptovirology threatens publish victim data perpetually block access unless ransom paid simple ransomware may lock system way difficult knowledgeable person reverse advanced malware uses technique called cryptoviral extortion encrypts victim files making inaccessible demands ransom payment decrypt properly implemented cryptoviral extortion attack recovering files without decryption key intractable problem – difficult trace digital currencies ukash bitcoin cryptocurrency used ransoms making tracing prosecuting perpetrators difficult ransomware attacks typically carried using trojan disguised legitimate file user tricked downloading opening arrives email attachment however one high-profile example wannacry worm travelled automatically computers without user interaction starting around 2012 use ransomware scams grown internationally 181.5 million ransomware attacks first six months 2018 marks 229 increase time frame 2017 june 2014 vendor mcafee released data showing collected double number samples ransomware quarter quarter previous year cryptolocker particularly successful procuring estimated us 3 million taken authorities cryptowall estimated us federal bureau investigation fbi accrued us 18 million june 2015 concept file-encrypting ransomware invented implemented young yung columbia university presented 1996 ieee security privacy conference called cryptoviral extortion inspired fictional facehugger movie alien cryptoviral extortion following three-round protocol carried attacker victim symmetric key randomly generated assist victims point attacker private key exposed victims victim need send small ciphertext encrypted symmetric-cipher key attacker ransomware attacks typically carried using trojan entering system example malicious attachment embedded link phishing email vulnerability network service program runs payload locks system fashion claims lock system e.g. scareware program payloads may display fake warning purportedly entity law enforcement agency falsely claiming system used illegal activities contains content pornography pirated media payloads consist simply application designed lock restrict system payment made typically setting windows shell even modifying master boot record and/or partition table prevent operating system booting repaired sophisticated payloads encrypt files many using strong encryption encrypt victim files way malware author needed decryption key payment virtually always goal victim coerced paying ransomware removed either supplying program decrypt files sending unlock code undoes payload changes attacker may simply take money without returning victim files attacker best interest perform decryption agreed since victims stop sending payments becomes known serve purpose key element making ransomware work attacker convenient payment system hard trace range payment methods used including wire transfers premium-rate text messages pre-paid voucher services paysafecard digital currency bitcoin 2016 survey commissioned citrix claimed larger businesses holding bitcoin contingency plans first known malware extortion attack aids trojan written joseph popp 1989 design failure severe necessary pay extortionist payload hid files hard drive encrypted names displayed message claiming user license use certain piece software expired user asked pay us 189 pc cyborg corporation order obtain repair tool even though decryption key could extracted code trojan trojan also known pc cyborg popp declared mentally unfit stand trial actions promised donate profits malware fund aids research idea abusing anonymous cash systems safely collect ransom human kidnapping introduced 1992 sebastiaan von solms david naccache electronic money collection method also proposed cryptoviral extortion attacks von solms-naccache scenario newspaper publication used since bitcoin ledgers exist time paper written notion using public key cryptography data kidnapping attacks introduced 1996 adam l. young moti yung young yung critiqued failed aids information trojan relied symmetric cryptography alone fatal flaw decryption key could extracted trojan implemented experimental proof-of-concept cryptovirus macintosh se/30 used rsa tiny encryption algorithm tea hybrid encrypt victim data since public key crypto used cryptovirus contains encryption key attacker keeps corresponding private decryption key private young yung original experimental cryptovirus victim send asymmetric ciphertext attacker deciphers returns symmetric decryption key contains victim fee long electronic money existed young yung proposed electronic money could extorted encryption well stating virus writer effectively hold money ransom half given even e-money previously encrypted user use user gets encrypted cryptovirus referred attacks cryptoviral extortion overt attack part larger class attacks field called cryptovirology encompasses overt covert attacks cryptoviral extortion protocol inspired parasitic relationship h. r. giger facehugger host movie alien examples extortionate ransomware became prominent may 2005 mid-2006 trojans gpcode troj.ransom.a archiveus krotten cryzip mayarchive began utilizing sophisticated rsa encryption schemes ever-increasing key-sizes gpcode.ag detected june 2006 encrypted 660-bit rsa public key june 2008 variant known gpcode.ak detected using 1024-bit rsa key believed large enough computationally infeasible break without concerted distributed effort encrypting ransomware returned prominence late 2013 propagation cryptolocker—using bitcoin digital currency platform collect ransom money december 2013 zdnet estimated based bitcoin transaction information 15 october 18 december operators cryptolocker procured us 27 million infected users cryptolocker technique widely copied months following including cryptolocker 2.0 thought related cryptolocker cryptodefense initially contained major design flaw stored private key infected system user-retrievable location due use windows built-in encryption apis august 2014 discovery trojan specifically targeting network-attached storage devices produced synology january 2015 reported ransomware-styled attacks occurred individual websites via hacking ransomware designed target linux-based web servers microsoft malware protection center identified trend away wsf files favour lnk files powershell scripting lnk shortcut files install locky ransomware automating infection operations rather relying traditional user downloads wsf files—all made possible universal powershell windows application unfortunately cybercriminals able leverage powershell attacks years recent report application found involved nearly 40 endpoint security incidents attackers finding weaknesses windows operating system years ’ clear ’ something problematic powershell scripting ransomware strains used proxies tied tor hidden services connect command control servers increasing difficulty tracing exact location criminals furthermore dark web vendors increasingly started offer technology service symantec classified ransomware dangerous cyber threat august 2010 russian authorities arrested nine individuals connected ransomware trojan known winlock unlike previous gpcode trojan winlock use encryption instead winlock trivially restricted access system displaying pornographic images asked users send premium-rate sms costing around us 10 receive code could used unlock machines scam hit numerous users across russia neighbouring countries—reportedly earning group us 16 million 2011 ransomware trojan surfaced imitated windows product activation notice informed users system windows installation re-activated due victim fraud online activation option offered like actual windows activation process unavailable requiring user call one six international numbers input 6-digit code malware claimed call would free routed rogue operator country high international phone rates placed call hold causing user incur large international long distance charges february 2013 ransomware trojan based stamp.ek exploit kit surfaced malware distributed via sites hosted project hosting services sourceforge github claimed offer fake nude pics celebrities july 2013 os x-specific ransomware trojan surfaced displays web page accuses user downloading pornography unlike windows-based counterparts block entire computer simply exploits behaviour web browser frustrate attempts close page normal means july 2013 21-year-old man virginia whose computer coincidentally contain pornographic photographs underage girls conducted sexualized communications turned police receiving deceived ransomware purporting fbi message accusing possessing child pornography investigation discovered incriminating files man charged child sexual abuse possession child pornography converse ransomware cryptovirology attack invented adam l. young threatens publish stolen information victim computer system rather deny victim access leakware attack malware exfiltrates sensitive host data either attacker alternatively remote instances malware attacker threatens publish victim data unless ransom paid attack presented west point 2003 summarized book malicious cryptography follows attack differs extortion attack following way extortion attack victim denied access valuable information pay get back attack presented victim retains access information disclosure discretion computer virus attack rooted game theory originally dubbed non-zero sum games survivable malware attack yield monetary gain cases malware acquires access information may damage victim user organization e.g. reputational damage could result publishing proof attack success increased popularity ransomware pc platforms ransomware targeting mobile operating systems also proliferated typically mobile ransomware payloads blockers little incentive encrypt data since easily restored via online synchronization mobile ransomware typically targets android platform allows applications installed third-party sources payload typically distributed apk file installed unsuspecting user may attempt display blocking message top applications another used form clickjacking cause user give device administrator privileges achieve deeper access system different tactics used ios devices exploiting icloud accounts using find iphone system lock access device ios 10.3 apple patched bug handling javascript pop-up windows safari exploited ransomware websites recently shown ransomware may also target arm architectures like found various internet-of-things iot devices industrial iot edge devices august 2019 researchers demonstrated possible infect dslr cameras ransomware digital cameras often use picture transfer protocol ptp standard protocol used transfer files researchers found possible exploit vulnerabilities protocol infect target camera ransomware execute arbitrary code attack presented defcon security conference las vegas proof concept attack actual armed malware 2012 major ransomware trojan known reveton began spread based citadel trojan based zeus trojan payload displays warning purportedly law enforcement agency claiming computer used illegal activities downloading unlicensed software child pornography due behaviour commonly referred police trojan warning informs user unlock system would pay fine using voucher anonymous prepaid cash service ukash paysafecard increase illusion computer tracked law enforcement screen also displays computer ip address versions display footage victim webcam give illusion user recorded reveton initially began spreading various european countries early 2012 variants localized templates branded logos different law enforcement organizations based user country example variants used united kingdom contained branding organizations metropolitan police service police national e-crime unit another version contained logo royalty collection society prs music specifically accused user illegally downloading music statement warning public malware metropolitan police clarified would never lock computer way part investigation may 2012 trend micro threat researchers discovered templates variations united states canada suggesting authors may planning target users north america august 2012 new variant reveton began spread united states claiming require payment 200 fine fbi using moneypak card february 2013 russian citizen arrested dubai spanish authorities connection crime ring using reveton ten individuals arrested money laundering charges august 2014 avast software reported found new variants reveton also distribute password-stealing malware part payload encrypting ransomware reappeared september 2013 trojan known cryptolocker generated 2048-bit rsa key pair uploaded turn command-and-control server used encrypt files using whitelist specific file extensions malware threatened delete private key payment bitcoin pre-paid cash voucher made within 3 days infection due extremely large key size uses analysts affected trojan considered cryptolocker extremely difficult repair even deadline passed private key could still obtained using online tool price would increase 10 btc—which cost approximately us 2300 november 2013 cryptolocker isolated seizure gameover zeus botnet part operation tovar officially announced u.s. department justice 2 june 2014 department justice also publicly issued indictment russian hacker evgeniy bogachev alleged involvement botnet estimated least us 3 million extorted malware shutdown september 2014 wave ransomware trojans surfaced first targeted users australia names cryptowall cryptolocker cryptolocker 2.0 unrelated original cryptolocker trojans spread via fraudulent e-mails claiming failed parcel delivery notices australia post evade detection automatic e-mail scanners follow links page scan malware variant designed require users visit web page enter captcha code payload actually downloaded preventing automated processes able scan payload symantec determined new variants identified cryptolocker.f unrelated original cryptolocker due differences operation notable victim trojans australian broadcasting corporation live programming television news channel abc news 24 disrupted half hour shifted melbourne studios due cryptowall infection computers sydney studio another trojan wave torrentlocker initially contained design flaw comparable cryptodefense used keystream every infected computer making encryption trivial overcome however flaw later fixed late-november 2014 estimated 9,000 users infected torrentlocker australia alone trailing turkey 11,700 infections another major ransomware trojan targeting windows cryptowall first appeared 2014 one strain cryptowall distributed part malvertising campaign zedo ad network late-september 2014 targeted several major websites ads redirected rogue websites used browser plugin exploits download payload barracuda networks researcher also noted payload signed digital signature effort appear trustworthy security software cryptowall 3.0 used payload written javascript part email attachment downloads executables disguised jpg images evade detection malware creates new instances explorer.exe svchost.exe communicate servers encrypting files malware also deletes volume shadow copies installs spyware steals passwords bitcoin wallets fbi reported june 2015 nearly 1,000 victims contacted bureau internet crime complaint center report cryptowall infections estimated losses least 18 million recent version cryptowall 4.0 enhanced code avoid antivirus detection encrypts data files also file names fusob one major mobile ransomware families april 2015 march 2016 56 percent accounted mobile ransomware fusob like typical mobile ransomware employs scare tactics extort people pay ransom program pretends accusatory authority demanding victim pay fine 100 200 usd otherwise face fictitious charge rather surprisingly fusob suggests using itunes gift cards payment also timer clicking screen adds users ’ anxiety well order infect devices fusob masquerades pornographic video player thus victims thinking harmless unwittingly download fusob fusob installed first checks language used device uses russian certain eastern european languages fusob nothing otherwise proceeds lock device demand ransom among victims 40 germany united kingdom united states following 14.5 11.4 respectively fusob lots common small another major family mobile ransomware represented 93 mobile ransomware 2015 2016 may 2017 wannacry ransomware attack spread internet using exploit vector named eternalblue leaked u.s. national security agency ransomware attack unprecedented scale infected 230,000 computers 150 countries using 20 different languages demand money users using bitcoin cryptocurrency wannacry demanded us 300 per computer attack affected telefónica several large companies spain well parts british national health service nhs least 16 hospitals turn away patients cancel scheduled operations fedex deutsche bahn honda renault well russian interior ministry russian telecom megafon attackers gave victims 7-day deadline day computers got infected encrypted files would deleted petya first discovered march 2016 unlike forms encrypting ransomware malware aimed infect master boot record installing payload encrypts file tables ntfs file system next time infected system boots blocking system booting windows ransom paid check point reported despite believed innovative evolution ransomware design resulted relatively-fewer infections ransomware active around time frame 27 june 2017 heavily modified version petya used global cyberattack primarily targeting ukraine affecting many countries version modified propagate using eternalblue exploit used wannacry due another design change also unable actually unlock system ransom paid led security analysts speculating attack meant generate illicit profit simply cause disruption 24 october 2017 users russia ukraine reported new ransomware attack named bad rabbit follows similar pattern wannacry petya encrypting user file tables demands bitcoin payment decrypt eset believed ransomware distributed bogus update adobe flash software among agencies affected ransomware interfax odessa international airport kiev metro ministry infrastructure ukraine used corporate network structures spread ransomware also discovered countries including turkey germany poland japan south korea united states experts believed ransomware attack tied petya attack ukraine especially bad rabbit code many overlapping analogical elements code petya/notpetya appending crowdstrike bad rabbit notpetya dll dynamic link library share 67 percent code though identity culprits names characters game thrones series embedded within code security experts found ransomware use eternalblue exploit spread simple method vaccinate unaffected machine running older windows versions found 24 october 2017 sites used spread bogus flash updating gone offline removed problematic files within days discovery effectively killing spread bad rabbit 2016 new strain ransomware emerged targeting jboss servers strain named samsam found bypass process phishing illicit downloads favor exploiting vulnerabilities weak servers malware uses remote desktop protocol brute-force attack guess weak passwords one broken virus behind attacks government healthcare targets notable hacks occurring town farmington new mexico colorado department transportation davidson county north carolina recently major breach security infrastructure atlanta mohammad mehdi shah mansouri born qom iran 1991 faramarz shahi savandi born shiraz iran 1984 wanted fbi allegedly launching samsam ransomware two allegedly made 6 million extortion caused 30 million damages using malware forms malware security software antivirus software might detect ransomware payload especially case encrypting payloads encryption way complete particularly new version unknown protective software distributed attack suspected detected early stages takes time encryption take place immediate removal malware relatively simple process completed would stop damage data without salvaging already lost security experts suggested precautionary measures dealing ransomware using software security policies block known payloads launching help prevent infection protect attacks keeping offline backups data stored locations inaccessible potentially infected computer external storage drives devices access network including internet prevents accessed ransomware installing security updates issued software vendors mitigate vulnerabilities leveraged certain strains propagate measures include cyber hygiene − exercising caution opening e-mail attachments links network segmentation keeping critical computers isolated networks furthermore mitigate spread ransomware measures infection control applied may include disconnecting infected machines networks educational programs effective communication channels malware surveillance ways collective participation number file systems keep snapshots data hold used recover contents files time prior ransomware attack event ransomware n't disable number tools intended specifically decrypt files locked ransomware although successful recovery may possible encryption key used files decryption tools use files uncorrupted backups encrypted copies known-plaintext attack jargon cryptanalysis works cipher attacker used weak begin vulnerable known-plaintext attack recovery key possible may take several days free ransomware decryption tools help decrypt files encrypted following forms ransomware aes_ni alcatraz locker apocalypse badblock bart btcware crypt888 cryptomix crysis encryptile findzip globe hidden tear jigsaw lambdalocker legion noobcrypt stampado szflocker teslacrypt xdata addition old copies files may exist disk previously deleted cases deleted versions may still recoverable using software designed purpose ransomware malicious software evolved since beginnings confined one two countries eastern europe spread across atlantic united states canada first versions type malware used various techniques disable computers locking victims system machine locker ransomware 133 examples ransomware works include locking screen displaying message branch local law enforcement indicating user ’ lines like “ browsed illicit materials must pay fine ” first seen russia year 2009 claiming message microsoft also used request payment sending sms message premium rate number next variant displayed pornographic image content demanded payment removal 2011 tactics changed attackers started use electronic payment methods added languages messages also changed based user ’ location obtained geo-locating user ’ ip addresses end users affected attacks corporations private entities government even hospitals also affected example healthcare although 2015 year largest ephi data breaches occurred according onc 2016 year ransomware started increase exponentially market according 2017 internet security threat report symantec corp ransomware affects systems also patient care clinical operations billing online criminals found “ easy money made healthcare ” according symantec report developed data insurance claims u.s. department health human services hhs ransomware growing rapidly across internet users also iot environment creates challenging problem infosec increasing attack surface area evolving sophisticated attacks becoming resistant time also accessible ever today cheap price attackers access ransomware service big problem millions dollars lost organizations industries decided pay hollywood presbyterian medical center medstar health end pressure offer services patients keep lives critical forced pay attacker knows problem paying ransom funding cybercrime according symantec 2019 istr report first time since 2013 2018 observed decrease ransomware activity drop 20 percent 2017 consumers preferred victims 2017 changed dramatically moved enterprises 2018 path accelerated 81 percent infections represented 12 percent increase common distribution method today based email campaigns cyber awareness training crucial detecting attacks whereas technology protect careless foolish behavior important organizations help users recognize malicious contact whereas ransomware typically introduced email social engineering techniques either download file provide key sensitive information take action bring harm organization according knowbe4 osterman report number approaches security awareness training practiced organizations managed security teams break room approach special meetings periodically held talk security monthly security videos short snippets security information simulated phishing tests target users internal phishing messages human firewall approach everyone subject simulated phishing employees prone attack identified do-nothing approach cyber awareness training exist organization effective successful cyber awareness training program must sponsored top organization supporting policies procedures effectively outline ramifications non-compliance frequency training process acknowledgement training without sponsorship “ c-level ” executives training ignored factors key successful cyber awareness training program establish baseline identifying level knowledge organization establish users knowledge prior training whichever approach organization decides implement important organization policies procedures place provide training date performed frequently backing entire organization top investment technology detect stop threats must maintained along need remember focus weakest link user publication proof-of-concept attack code common among academic researchers vulnerability researchers teaches nature threat conveys gravity issues enables countermeasures devised put place however lawmakers support law-enforcement bodies contemplating making creation ransomware illegal state maryland original draft hb 340 made felony create ransomware punishable 10 years prison however provision removed final version bill minor japan arrested creating distributing ransomware code young yung ansi c source code ransomware cryptotrojan on-line cryptovirology.com since 2005 part cryptovirology book written source code cryptotrojan still live internet associated draft chapter 2
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Computer security
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dg/ux dg/ux discontinued unix operating system developed data general eclipse mv minicomputer line later aviion workstation server line motorola 88000 intel ia-32-based variants dg/ux 1.00 released march 1985 based unix system v release 2 additions 4.1bsd 1987 dg/ux 3.10 released 4.2bsd tcp/ip networking nfs x window system included dg/ux 4.00 1988 comprehensive re-design system based system v release 3 supporting symmetric multiprocessing eclipse mv 4.00 filesystem based aos/vs ii filesystem using logical disk facility could span multiple disks dg/ux 5.4 released around 1991 replaced legacy unix file buffer cache unified demand paged virtual memory management later versions based system v release 4 aviion dg/ux supported multiprocessor machines time variants unix operating system also complete unix variants example operating system included full c compiler gcc also logical volume manager os small compact rich features simple easy install require vast resources memory processing power example six-way pentium pro-based aviion would support several hundred users using text terminals volume manager built os simple powerful disk administration could performed online without taking file system offline included extending relocating mirroring shrinking functions could performed swap area allowing in-place migrations disk storage without downtime dg/ux 5.4 supported filesystem shrinking split mirror online backup filesystems 2 tb filesystem journaling 1991 vendors offered similar features time later versions added support processor memory affinity support high-end multiprocessor numa aviion system
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Operating systems
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ofono ofono free software project mobile telephony gsm/umts applications built 3gpp standards uses high-level d-bus api use telephony applications ofono free software released terms gnu general public license v2 ofono jointly announced linux intel nokia nokia since shipped ofono meego-based n9 meego project ended intel collaborated samsung new linux-based project named tizen first release tizen contained another telephony stack 2012 announced replace ofono early 2013 canonical ltd announced ubuntu touch also uses ofono another successor project meego sailfish os also uses ofono telephony since version 1.4 released august 2016 networkmanager use ofono modem manager
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Operating systems
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instance variable object-oriented programming classes instance variable variable defined class i.e member variable instantiated object class separate copy instance instance variable similar class variable instance variable variable declared class outside constructor method/function instance variables created object instantiated accessible methods constructor block class access modifiers given instance variable instance variable class variable although similarities type class attribute class property field data member dichotomy instance class members applies methods member functions well class may instance methods class methods instance variable lives memory life object owned variables properties object knows instances object copies instance variables even value one object another one object instance change values instance variables without affecting instances instance variables used methods class unless method declared static c++ example instance variable codice_1 copy class variable codice_2 instance constructed assigned sequential value codice_3 incremented since codice_4 instance variable codice_5 object contains distinct value contrast one object codice_2 available instances value
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Programming language topics
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gran turismo official steering wheel gran turismo official steering wheels gt force driving force see trademark symbols difference series steering wheels designed logitech a.k.a logicool japan collaboration polyphony digital racing games controllers designed used playstation 2 playstation 3 systems later models used pc well due usb connection gt force central part driving simulation cockpit installation official kits co-designed released japan logicool sparco distributed import tuner endless north america compatible kits designed released worldwide european manufacturers playseat® movetech features common models include features vary models original gt force first came japan south east asia 2001 later released north america europe brand soon evolved driving force logitech distributed territories code product lprc logicool playstation racing controller 2007 gt force line-up made three wheels entry-level gt force rx replacing discontinued driving force type 79.99 usd/eur medium-level gt force pro 129.98 usd/eur g25 racing wheel replaced first top level 299.99 usd/eur compatible playstation 2 playstation 3 windows pc systems supported gran turismo 5 prologue gt force lprc-10000 rebranded logitech wingman formula gp blue rather yellow rubber grip released april 28 2001 official wheel gt force gran turismo 2000 lprc-10001 scheduled 2001 however due game title change replaced gt force gran turismo 3 a-spec custom version released april 28 2001 june 26 2003 logicool released initial special stage custom version gt force lprc-10000 driving force first evolution gt force announced london games convention early september 2001 model discontinued since replaced driving force pro 2003 driving force pro also known gt force pro lprc-11000 gran turismo 4 prologue official wheel released december 2003 sega rally 2006 custom version named released january 12 2006 manufactured logitech playstation 2 primarily well compatible select pc games wheel featured force feedback 900 degree rotation wheel offers analogue accelerator brake pedals sequential gear shift side paddle shifters mounted back wheel addition standard playstation 2 buttons controller jointly designed logitech polyphony digital used gran turismo 4 however works games compatible 900 degree rotation switching 200 degree mode wheel received strong praise reviewers launch overall good experience paired gran turismo 4 logitech website lists playstation 3 system requirements indicating supported 900° support software dependent driving force ex also known gt force rx lprc-12000 driving force rx retail version playstation 3 official wheel released console launch date november 11 2006 features force feedback succeeded driving force gt wheel came bundled formula one championship edition driving force gt released december 13 2007 developed conjunction polyphony digital first introduced 2007 tokyo game show intended use gran turismo 5 prologue gran turismo 5 playstation 3 auto racing games driving force gt fifth entry company driving force series game controllers g25 racing wheel lprc-13000 unveiled october 25 2007 released december 13 2007 currently matching official racing cockpit available official gt steering wheel fully compatible updates officially supported gt5 gt6 g27 racing wheel based upon previous g25 new features like g25 g27 also official gt steering wheel fully compatible updates officially supported gt5 gt6 g29 driving force racing wheel based upon g27 driving force gt compatible playstation 3 playstation 4 pc released 2015 replace g27 like g27 also official gran turismo steering wheel however supported gran turismo latest installment gran turismo sport
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Computer architecture
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national white collar crime center national white collar crime center also known nw3c congressionally funded non-profit corporation trains state local law enforcement agencies combat emerging economic cyber crime problems nw3c provides general public information research preventing economic cyber crime national white collar crime center provides training investigative support research organizations involved preventing investigating prosecuting economic high tech crime
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Computer security
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john backus john warner backus december 3 1924 – march 17 2007 american computer scientist directed team invented implemented fortran first widely used high-level programming language inventor backus–naur form bnf widely used notation define formal language syntax later research function-level programming paradigm presenting findings influential 1977 turing award lecture programming liberated von neumann style ieee awarded backus w. w. mcdowell award 1967 development fortran received national medal science 1975 1977 acm turing award profound influential lasting contributions design practical high-level programming systems notably work fortran publication formal procedures specification programming languages retired 1991 died home ashland oregon march 17 2007 backus born philadelphia grew nearby wilmington delaware studied hill school pottstown pennsylvania apparently diligent student entering university virginia study chemistry quit conscripted u.s. army began medical training haverford college internship hospital diagnosed cranial bone tumor successfully removed plate installed head ended medical training nine months subsequent operation replace plate one design moving new york city trained initially radio technician became interested mathematics graduated columbia university bachelor degree 1949 master degree 1950 mathematics joined ibm 1950 first three years worked selective sequence electronic calculator ssec first major project write program calculate positions moon 1953 backus developed language speedcoding first high-level language created ibm computer aid software development ibm 701 computer programming difficult time 1954 backus assembled team define develop fortran ibm 704 computer fortran first high-level programming language put broad use backus served international committees developed algol 58 influential algol 60 quickly became de facto worldwide standard publishing algorithms backus developed backus–naur form bnf unesco report algol 58 formal notation able describe context-free programming language important development compilers deviations approach tried—notably lisp apl—but 1970s following development automated compiler generators yacc backus–naur context-free specifications computer languages become quite standard contribution helped backus win turing award 1977 backus later worked function-level programming language known fp described turing award lecture programming liberated von neumann style sometimes viewed backus apology creating fortran paper less garner interest fp language spark research functional programming general backus publicized function-level style programming message mostly misunderstood traditional functional programming style languages fp strongly inspired kenneth e. iverson apl even using non-standard character set fp interpreter distributed 4.2bsd unix operating system relatively implementations language used educational purposes backus spent latter part career developing fl function level successor fp fl internal ibm research project development language stopped project finished papers documenting remain source code compiler described made public fl odds functional programming languages developed 1980s based lambda calculus static typing systems instead apl concatenation primitive operations many language ideas implemented versions j programming language iverson successor apl
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Programming language topics
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inverse multiplexer inverse multiplexer often abbreviated inverse mux imux allows data stream broken multiple lower data rate communication links inverse multiplexer differs demultiplexer multiple output streams former stay inter-related whereas latter unrelated inverse multiplexer opposite multiplexer divides one high-speed link multiple low-speed links whereas multiplexer combines multiple low-speed links one high-speed link provides end end connection several times data rate available low rate data links note multiplexers links often used bi-directional pairs either end link inverse multiplexer combined reverse inverse demultiplexer still called inverse mux inverse multiplexers used example combine number isdn channels together one high rate circuit higher rate connection available single isdn connection needed typically useful areas higher rate circuits available alternative inverse multiplexer use three separate links load sharing data case ip network packets could sent round-robin mode separate link advantages using inverse multiplexing separate links include simple analogy transport help explain distinction multiplexing inverse multiplexing small cargoes pencils shipped overseas generally carried one time rather assembled small boxes grouped larger cartons go intermodal containers join multiple containers aboard container ship step analogous multiplexing process conversely large cargo example structure relocation may disassembled carriage multiple vehicles reassembled correct order destination analogous inverse multiplexing
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Internet protocols
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encrypting file system encrypting file system efs microsoft windows feature introduced version 3.0 ntfs provides filesystem-level encryption technology enables files transparently encrypted protect confidential data attackers physical access computer efs available versions windows developed business environments see supported operating systems windows 2000 onwards default files encrypted encryption enabled users per-file per-directory per-drive basis efs settings also mandated via group policy windows domain environments cryptographic file system implementations operating systems available microsoft efs compatible see also list cryptographic file systems operating system running system without file encryption access files normally goes os-controlled user authentication access control lists however attacker gains physical access computer barrier easily circumvented one way example would remove disk put another computer os installed read filesystem another would simply reboot computer boot cd containing os suitable accessing local filesystem widely accepted solution store files encrypted physical media disks usb pen drives tapes cds microsoft windows family operating systems efs enables measure although ntfs drives using combination public key cryptography symmetric key cryptography make decrypting files extremely difficult without correct key however cryptography keys efs practice protected user account password therefore susceptible password attacks words encryption file strong password unlock decryption key efs works encrypting file bulk symmetric key also known file encryption key fek uses symmetric encryption algorithm takes less time encrypt decrypt large amounts data asymmetric key cipher used symmetric encryption algorithm used vary depending version configuration operating system see algorithms used windows version fek symmetric key used encrypt file encrypted public key associated user encrypted file encrypted fek stored efs alternative data stream encrypted file decrypt file efs component driver uses private key matches efs digital certificate used encrypt file decrypt symmetric key stored efs stream efs component driver uses symmetric key decrypt file encryption decryption operations performed layer ntfs transparent user applications folders whose contents encrypted file system marked encryption attribute efs component driver treats encryption attribute way analogous inheritance file permissions ntfs folder marked encryption default files subfolders created folder also encrypted encrypted files moved within ntfs volume files remain encrypted however number occasions file could decrypted without user explicitly asking windows files folders decrypted copied volume formatted another file system like fat32 finally encrypted files copied network using smb/cifs protocol files decrypted sent network significant way preventing decryption-on-copy using backup applications aware raw apis backup applications implemented raw apis simply copy encrypted file stream efs alternative data stream single file words files copied e.g backup file encrypted form decrypted backup starting windows vista user private key stored smart card data recovery agent dra keys also stored smart card two significant security vulnerabilities existed windows 2000 efs variously targeted since windows 2000 local administrator default data recovery agent capable decrypting files encrypted efs local user efs windows 2000 function without recovery agent always someone decrypt encrypted files users non-domain-joined windows 2000 computer susceptible unauthorized efs decryption anyone take local administrator account trivial given many tools available freely internet windows xp later default local data recovery agent requirement one setting syskey mode 2 3 syskey typed bootup stored floppy disk mitigate risk unauthorized decryption local administrator account local user password hashes stored sam file encrypted syskey syskey value available offline attacker possess syskey passphrase/floppy windows 2000 user rsa private key stored truly encrypted form also backup user rsa private key weakly protected attacker gains physical access windows 2000 computer resets local user account password attacker log user recovery agent gain access rsa private key decrypt files backup user rsa private key encrypted lsa secret accessible attacker elevate login localsystem trivial given numerous tools internet windows xp beyond user rsa private key backed using offline public key whose matching private key stored one two places password reset disk windows xp member domain active directory windows xp member domain means attacker authenticate windows xp localsystem still access decryption key stored pc hard drive windows 2000 xp later user rsa private key encrypted using hash user ntlm password hash plus user name – use salted hash makes extremely difficult reverse process recover private key without knowing user passphrase also setting syskey mode 2 3 syskey typed bootup stored floppy disk mitigate attack since local user password hash stored encrypted sam file user logged successfully access efs encrypted data requires additional authentication decryption happens transparently thus compromise user password automatically leads access data windows store versions user account passphrases reversible encryption though longer default behaviour also configured store default original version windows xp lower lan manager hashes local user account passphrases attacked broken easily also stores local user account passphrases ntlm hashes fairly easily attacked using rainbow tables passwords weak windows vista later versions n't allow weak passwords default mitigate threat trivial brute-force attacks local passphrases older versions windows need configured using security settings portion group policy never store lm hashes course enable autologon stores plaintext passphrases registry using local user account passphrases 14 characters long prevents windows storing lm hash sam – added benefit making brute-force attacks ntlm hash harder encrypting files efs – converting plaintext files encrypted files – plaintext files wiped simply deleted i.e data blocks flagged use filesystem means unless example happen stored ssd trim support easily recovered unless overwritten fully mitigate known non-challenging technical attacks efs configure encryption folder level temporary files like word document backups created directories also encrypted wish encrypt individual files copy encrypted folder encrypt file place securely wipe disk volume use windows cipher utility /w option wipe free space including still contains deleted plaintext files various third-party utilities may work well anyone gain administrators access overwrite override change data recovery agent configuration serious issue since attacker example hack administrator account using third-party tools set whatever dra certificate want data recovery agent wait sometimes referred two-stage attack significantly different scenario risk due lost stolen pc highlights risk due malicious insiders user encrypts files first stage attack feks automatically encrypted designated dra public key attacker needs access computer administrator gain full access subsequently efs-encrypted files even using syskey mode 2 3 protect attack attacker could back encrypted files offline restore elsewhere use dra private key decrypt files course malicious insider gain physical access computer might consider security features irrelevant could also install rootkits software even hardware keyloggers etc computer – potentially much interesting effective overwriting dra policy files encrypted efs decrypted using rsa private key matching previously used public key stored copy user private key ultimately protected user logon password accessing encrypted files outside windows operating systems linux example possible — least currently third party efs component driver using special tools reset user login password render impossible decrypt user private key thus useless gaining access user encrypted files significance occasionally lost users resulting data loss user forgets password fails back encryption key led coining term delayed recycle bin describe seeming inevitability data loss inexperienced user encrypts files efs configured use keys issued public key infrastructure pki configured enable key archival recovery encrypted files recovered recovering private key first operating systems file systems native support efs windows efs supports range symmetric encryption algorithms depending version windows use files encrypted
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Computer file systems
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gameover zeus gameover zeus peer-to-peer botnet based components earlier zeus trojan malware created evgeniy mikhailovich bogachev russia believed spread use cutwail botnet unlike predecessor zeus trojan gameover zeus uses encrypted peer-to-peer communication system communicate nodes command control servers greatly reducing vulnerability law enforcement operations algorithm used appears modeled kademlia p2p protocol scammers control monitor gameover zeus via command control c c server virus establishes connection server soon malicious executable installs computer disables certain system processes download launch executables even delete essential system files easily bricking device according report symantec gameover zeus largely used banking fraud distribution cryptolocker ransomware early june 2014 u.s. department justice announced international inter-agency collaboration named operation tovar succeeded temporarily cutting communication gameover zeus command control servers effort shut evgeniy mikhailovich bogachev criminal infrastructure liberate computers infected gameover zeus indicted united states accused creating sprawling network virus-infected computers siphon hundreds millions dollars bank accounts around world targeting anyone enough money worth stealing widely circulated photo pictured holding domestic bengal cat bitdefender identified two gameover zeus variants wild one generates 1,000 domains per day generates 10,000 per day 24 february 2015 fbi announced reward 3 million exchange information regarding alleged russian cyber criminal evgeniy mikhailovich bogachev known online aliases « slavik » « lucky12345 » « pollingsoon » « monstr » « ioo » « nu11 » suspected association gameover zeus fbi reward 3 million highest ever cybercriminal
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Distributed computing architecture
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co-managed security co-managed security service model entails security monitoring event correlation incident response system tuning compliance support across organization entire environment co-management allows organizations collaborate service providers blending security expertise provider contextual knowledge customer optimize security posture co-managed security services also allow organizations ’ critical data tools remotely managed team certified engineers security analysts 24/7/365 security operations center soc service approach allows customer data remain in-house siem platform either on-site cloud-hosted service provider staff works conjunction customer security teams outline rules engagement inside environment provide monitoring respond alerts real-time security operation center also provide “ care feeding ” development variety security solutions co-managed approach also allows organizations focus emerging internal projects critical areas according gartner use co-managed security information event management report “ co-managed siem services enable security risk management leaders maximize value siem enhance security monitoring capabilities retaining control flexibility. ” co-management rise expected grow five-fold 2020 siem ids/ips compliance automation network configuration management tools advanced threat intelligence network access control endpoint threat detection response application security file integrity monitoring forensic investigation vulnerability scanning assessment examples cyber security solutions co-managed service providers support
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Computer security
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compaq presario m2000 many models compaq presario m2000 ran intel celeron processor although also made amd turion 64 amd mobile sempron processors hard drive 40 gb 5400 rpm br display 15 glare type lcd br processor intel celeron 1.4 ghz amd turion ml-28 1.6ghz amd sempron br os provided windows xp home edition standard br memory expandable 1024mb ram br jacks inputs special buttons notifications connectivity security kensington lock slot
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Computer architecture
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david turner computer scientist david a. turner born 1946 british computer scientist best known designing implementing first functional programming languages based lazy evaluation combinator graph reduction polymorphic types sasl 1972 krc 1981 commercially supported miranda 1985 miranda strong influence later haskell programming language d.phil university oxford held professorships queen mary college london university texas austin university kent canterbury spent career retains title emeritus professor computation also emeritus professor middlesex university england
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Programming language topics
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powerpc e5500 powerpc e5500 64-bit power isa-based microprocessor core freescale semiconductor core implements core power isa v.2.06 hypervisor support altivec four issue seven-stage out-of-order pipeline double precision fpu three integer units 32/32 kb data instruction l1 caches 512 kb private l2 cache per core 2 mb shared l3 cache speeds range 2.5 ghz core designed highly configurable via corenet fabric meet specific needs embedded applications features like multi-core operation interface auxiliary application processing units apu e5500 based e500mc core adds new instructions introduced power isa 2.06 specification namely byte- bit-level acceleration parity population count bit permute compare byte fpu taken straight powerpc e600 core classic fully pipelined dual precision ieee 754 unit running full core speed supports conversion 64-bit floats integers effectively twice fast fpu e500mc e5500 also introduces enhanced branch prediction unit 8-entry link stack e5500 core first 64-bit power isa core designed solely freescale introduced freescale technology forum june 2010 simulated models available july 2010 hard samples late 2010 full scale manufacturing second half 2011 freescale used e700 ng-64 monikers refer similarly speced core since 2004 product e5500 powers high-performance qoriq p5 system chip soc family share common naming scheme p50x0 bae systems built radiation hardened computer based e5500 core devices space
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Computer architecture
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fruity frank fruity frank 1984 computer game amstrad cpc msx home computers produced kuma software authored steve wallis graphics brother sean wallis gameplay similar mr though story involves frank protecting garden invading monsters player collect fruits lying around garden avoiding touching monsters apples pushed kill offer temporary respite monsters also killed throwing bouncing apple pip pieces fruit collected player proceeds next level level identifiable different colour background new jocular tune music game inspired traditional english songs rhymes fruity frank four types enemies every 1 000 points frank gains extra life maximum two 100 000 points reached counter set back 0
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Computer architecture
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power processing element power processing unit ppu 64-bit dual-threaded in-order powerpc 2.02 microprocessor core designed ibm use primarily game consoles playstation 3 xbox 360 also found applications high performance computing supercomputers record setting ibm roadrunner instances ppu joined 512 kb l2 cache form called power processing element ppe ppu used main cpu core three different processor designs ppu in-order processor unique traits allow achieve benefits out-of-order execution without expensive re-ordering hardware upon reaching l1 cache miss execute past cache miss stopping instruction actually dependent load send 8 load instructions l2 cache out-of-order instruction delay pipe side path allows execute instructions would normally cause pipeline stalls without holding rest pipeline instruction delay pipeline used out-of-order load/stores cache misses put moves ppe 23 stage general pipeline additional 11 stages possible microcode additional 4 stages possible branch prediction ppu runs two hardware threads simultaneously main registers code execution duplicated exception interrupt-handling registers several essential arrays queues generate exceptions simultaneously perform branch prediction individual branch histories execution engine caches duplicated though still single-core design 64-bit double precision floating-point unit 128-bit vmx unit using altivec instruction set perform theoretical 12 floating-point operations per cycle floating-point unit floating-point multiply-adds come smaller 64-bits gives 3.2 billion clock cycles 12 38.4 billion floating-point operations/second ppu enhanced powerxcell 8i processor able make single cycle double precision floating point operations tailored high performance computing supercomputers vmx unit xcpu xbox 360 enhanced 128 registers entirely compatible regular altivec
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Computer architecture
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bernard ardisana brigadier general bernard ardisana born 1924 died 1978 assistant deputy director operations national security agency fort george g. meade tenure us military also commanded usaf security service ’ 6924th security squadron went become vice commander usaf security service died january 14 1978 heart attack kimbrough army hospital ft. meade bernard ardisana born october 27 1924 tampa florida immediately completing high school 1943 enlisted u.s. army signal corps took position radio engineer stayed military three years returning civilian life attending university illinois graduated 1949 bachelor science degree economics 1966 officer air force reserve earned master arts degree education lady lake university san antonio texas april september 1961 ardisana attended graduated air command staff college maxwell air force base 1972 attended air war college maxwell air force base ardisana worked several u.s. military agencies including air force nsa army signal corps march 1952 called active duty train brooks air force base student traffic-analysis upon completion training august transferred washington dc work language officer armed forces security agency 1956 transferred fort meade developed new analysis techniques still use today 1958 transferred zweibrücken germany developed operations communications system still used cryptography community today 1963 1965 served chief operations inspection team kelly air force base san antonio texas 1966 became head operations systems evaluation management branch u.s. air force security service directorate operations 1967 1970 served vietnam various positions sent frankfurt germany act assistant deputy chief staff operations european security region returned united states 1972 1973 assigned ft. meade serve part national security agency stayed two years becoming vice commander u.s. air force security service retained position two years well returning nsa assistant deputy director operations ardisana died january 14 1978 kimbrough army hospital ft. meade heart attack serving nsa assistant deputy director operations ardisana expertise cryptography allowed develop number important changes usaf cryptologic operations procedures much work designing operations communications remained standard 25 years within us air force work key concept allowed development critical intelligence communication system
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Computer security
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dc computer program dc desk calculator cross-platform reverse-polish calculator supports arbitrary-precision arithmetic one oldest unix utilities predating even invention c programming language like utilities vintage powerful set features terse syntax traditionally bc calculator program infix notation implemented top dc article provides examples attempt give general flavour language complete list commands syntax one consult man page one specific implementation dc oldest surviving unix language home bell labs received pdp-11 dc—written b—was first language run new computer even assembler multiply four five dc note whitespace optional also get result commands translates push four five onto stack multiplication operator pop two elements stack multiply push result back stack p command used examine print screen top element stack q command quits invoked instance dc note numbers must spaced even operators need arithmetic precision changed command k sets number fractional digits number digits following point used arithmetic operations since default precision zero sequence commands produces 0 result adjusting precision k arbitrary number decimal places produced command sequence outputs '.66666 evaluate formula_1 v computes square root top stack used input negative number swap top two elements stack use r command duplicate top element use 'd command read line stdin use command evaluate line dc command necessary syntactically correct potentially security problem since dc command allow arbitrary command execution mentioned p print top stack newline n pop top stack output without trailing newline f dump entire stack one entry per line dc also supports arbitrary input output radices command pop top stack use input base hex digits must upper case avoid collisions dc commands limited a-f input radix larger 16 command output base keep mind input base affect parsing every numeric value afterwards usually advisable set output base first read values k commands push current precision input radix output radix top stack example convert hex binary addition basic arithmetic stack operations dc includes support macros conditionals storing results later retrieval mechanism underlying macros conditionals register dc storage location single character name stored retrieved 'sc pops top stack stores register c 'lc pushes value register c onto stack example registers also treated secondary stacks values pushed popped main stack using l commands string values enclosed characters may pushed stack stored registers command convert low order byte numeric value ascii character top stack string replace first character string ways build strings perform string manipulation executing x command printing p command character begins comment end line macros implemented allowing registers stack entries strings well numbers string printed also executed i.e processed sequence dc commands instance store macro add one multiply 2 register using x command executes top stack use like finally use macro mechanism provide conditionals command '=r pop two values stack execute macro stored register r equal print string 'equal top stack equal 5 conditionals execute specified macro top two values stack greater less equal greater less greater equal less equals respectively looping possible defining macro conditionally reinvokes simple factorial top stack might implemented '1q command exit macro allowing early return q quit two levels macros dc less two levels call stack z push current stack depth z operation print prime numbers example relatively simple program dc command 1 line convert distances metres feet inches bulk concerned prompting input printing output suitable format looping round convert another number example implementation euclidean algorithm find greatest common divisor|gcd category cross-platform software category unix software category software calculators category free mathematics software category numerical programming languages category stack-oriented programming languages
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Programming language topics
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cdb software cdb short constant database refers library data format created daniel j. bernstein cdb acts on-disk associative array mapping keys values allows multiple values stored single key constant database allows two operations creation reading operations designed fast highly reliable since database change use multiple processes access single database without locking additionally since modifications actually creation replacement database take advantage unix filesystem semantics provide guarantee reliability record positions key value lengths hash values 32-bit quantities stored 4 bytes thus cdb must fit 4 gigabytes cdb used djbdns fastforward mess822 qmail ucspi-tcp provide highly efficient reliable simple data access database contains entire data set e.g single associative array single computer file consists three parts fixed-size header data set hash tables lookups designed exact keys though types searches could performed scanning entire database lookups performed using following algorithm lookups keys multiple values additional values may found simply resuming search next slot numbers—offsets lengths hash values—are unsigned 32-bit integers stored little endian format keys data considered opaque byte strings special treatment fixed-size header beginning database describes 256 hash tables listing position within file length slots data stored series records storing key length data length key data alignment sorting rules records followed set 256 hash tables varying lengths since zero valid length may fewer 256 hash tables physically stored database nonetheless considered 256 tables hash tables contain series slots contains hash value record offset empty slots offset zero hashes unsigned 32 bit integers start value 5381 byte key current hash multiplied 33 xor'ed current byte key overflow bits discarded slots tables trivially computed hashes target table simply lowest eight bits hash i.e hash modulo 256 slot within table remaining bits hash modulo table length i.e hash divided 256 modulo table length official cdb library code public domain individual source files marked also available public domain djbdns package however rest cdb package used license-free software meaning must distributed verbatim unusual licensing simplicity format prompted others re-implement library release common terms michael tokarev tinycdb library available public domain 2009 cdb put public domain notably creator cdb intend cdb used shared library differs virtually similar databases berkeley db
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Databases
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sshfp record secure shell fingerprint record abbreviated sshfp record type resource record domain name system dns identifies ssh keys associated host name acquisition sshfp record needs secured mechanism dnssec chain trust established example host domain name codice_1 uses dsa key sha-1 fingerprint codice_2
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Internet protocols
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disk mirroring data storage disk mirroring replication logical disk volumes onto separate physical hard disks real time ensure continuous availability commonly used raid 1 mirrored volume complete logical representation separate volume copies disaster recovery context mirroring data long distance referred storage replication depending technologies used replication performed synchronously asynchronously semi-synchronously point-in-time replication enabled via microcode disk array controller via server software typically proprietary solution compatible various data storage device vendors mirroring typically synchronous synchronous writing typically achieves recovery point objective rpo zero lost data asynchronous replication achieve rpo seconds remaining methodologies provide rpo minutes perhaps several hours disk mirroring differs file shadowing operates file level disk snapshots data images never re-synced origins recognized disks inherently unreliable component computer systems mirroring technique allow system automatically maintain multiple copies dual backup meaning data redundant hard drives exist mirror data event disk hardware failure system continue process quickly recover data mirroring may done locally specifically cater disk unreliability may done remotely forms part sophisticated disaster recovery scheme may done locally remotely especially high availability systems normally data mirrored onto physically identical drives though process applied logical drives underlying physical format hidden mirroring process typically mirroring provided either hardware solutions disk arrays software within operating system linux mdadm device mapper additionally file systems like btrfs zfs provide integrated data mirroring additional benefits btrfs zfs maintain data metadata integrity checksums making capable detecting bad copies blocks using mirrored data pull data correct blocks several scenarios happens disk fails hot swap system event disk failure system typically diagnoses disk failure signals failure sophisticated systems may automatically activate hot standby disk use remaining active disk copy live data onto disk alternatively new disk installed data copied less sophisticated systems system operated remaining disk spare disk installed copying data one side mirror pair another called rebuilding less commonly resilvering mirroring performed site site either rapid data links example fibre optic links distances 500 maintain adequate performance support real-time mirroring longer distances slower links maintain mirrors using asynchronous copying system remote disaster recovery systems mirroring may done integrated systems simply additional applications master slave machines addition providing additional copy data purpose redundancy case hardware failure disk mirroring allow disk accessed separately reading purposes certain circumstances significantly improve performance system choose read disk seek quickly required data especially significant several tasks competing data disk thrashing switching tasks takes time task reduced important consideration hardware configurations frequently access data disk implementations mirrored disk split used data backup allowing first disk remain active however merging two disks may require synchronization period write i/o activity occurred mirrored disk mirroring schemes employ three disks two disks redundancy mirroring third split performing backups emc nomenclature third disks called business continuance volumes bcvs
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Computer architecture
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apache karaf apache karaf modular open source osgi release 6 runtime environment project became top level project 2010 previously subproject apache servicemix apache karaf work top two used osgi frameworks apache felix equinox osgi providing additional features karaf container modern polymorphic container lightweight powerful enterprise ready container powered osgi polymorphic means karaf host kind applications osgi spring war much karaf use standalone container bootstrap way using karaf boot karaf cellar clustering solution karaf allows manage multiple instances synchronization instances latest release 4.1.3 february 25 2019 karaf cave implementation osgi repository specification used karaf features resolver provide resources dealing requirements capabilities artifacts latest release 4.1.2 january 19 2019 decanter provides ready use monitoring solution including alerting key feature bam business activities monitoring also completely extensible customizable latest release 2.2.0 march 22 2019
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Web technology
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riskware riskware portmanteau risk software word used describe software whose installation execution poses possible yet definite risk host computer relatively normal programs often fall category riskware applications modified another purpose used computer user owner
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Computer security
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bioctl bio 4 pseudo-device driver bioctl 8 utility implement generic raid volume management interface openbsd netbsd idea behind software similar ifconfig single utility operating system used control raid controller using generic interface instead rely plentiful proprietary custom raid management utilities specific given hardware raid manufacturer features include monitoring health status arrays controlling identification blinking leds managing sound alarms specifying hot spare disks additionally codice_1 configuration openbsd delegated bioctl well whereas initial creation volumes configuration hardware raid left card bios non-essential operating system already booted interfacing kernel userland performed codice_2 system call codice_3 pseudo-device bio/bioctl subsystem deemed important part openbsd advocacy open hardware documentation 3.8 release title titular song dedicated topic — hackers lost raid development took place time controversy adaptec refused release appropriate hardware documentation necessary order make aac 4 driver work reliably followed openbsd disabling support driver commentary 3.8 release developers express irony hardware raid controllers supposed purpose providing reliability redundancy repair whereas reality many vendors expect system administrators install depend huge binary blobs order assess volume health service disk arrays specifically openbsd making reference modus operandi freebsd documentation aac 4 driver adaptec specifically suggests enabling linux compatibility layer order use management utilities documentation even fails explain exactly utilities must obtained versions would compatible evidently proprietary tools may expired likewise openbsd developers intentionally chose concentrate supporting basic features controller uniform across brands variations specifically fact initial configuration controller must still made card bios never kept secret bio/bioctl announcement contrasted approach taken freebsd example individual utilities exist several independent raid drivers interface utility independent one another specifically freebsd includes separate device-specific utilities called codice_4 codice_5 codice_6/codice_7 codice_8 provides many options least subtle differences interface configuration management controllers contributes code bloat mention additional drivers tool even exists open-source software openbsd 6.4 2018 dozen drivers register bio framework monitoring state logical drive also duplicated hardware monitoring frameworks corresponding utilities systems bioctl available — hw.sensors sensorsd openbsd sysmon envsys envstat powerd netbsd example openbsd since 4.2 release status drive sensors could automatically monitored simply starting sensorsd without specific configuration required drivers converted use bio sensors frameworks release openbsd scsi enclosure services ses saf-te supported since openbsd 3.8 2005 well feature led blinking bio bioctl implementing codice_10 ioctl helping system administrators identify devices within enclosures service additionally ses saf-te drivers openbsd feature support combination temperature fan sensors psu doorlock alarm indicators auxiliary sensor data exported hw.sensors framework openbsd monitored familiar tools like sysctl snmp sensorsd netbsd older ses/saf-te driver nasa 2000 still place integrated bio envsys device files unique ioctl interface featuring custom scsi-specific userland tooling older implementation also available openbsd 2000 2005 removed 2005 together userland tools new leaner bio- hw.sensors-based alternative drivers introduced ses saf-te kept two separate drivers openbsd n't require separate custom userland utilities anymore reducing code bloat number source lines code
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Operating systems
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virustotal virustotal website created spanish security company hispasec sistemas launched june 2004 acquired google inc. september 2012 company ownership switched january 2018 chronicle subsidiary alphabet inc.. virustotal aggregates many antivirus products online scan engines check viruses user antivirus may missed verify false positives files 550 mb uploaded website sent via email anti-virus software vendors receive copies files flagged scans passed engine help improve software extension virustotal capability users also scan suspect urls search virustotal dataset virustotal dynamic analysis malware uses cuckoo sandbox virustotal selected pc world one best 100 products 2007 virustotal windows uploader application integrates explorer right-click contextual menu listed send virus total application also launches manually submitting url program currently running os virustotal stores name various hashes scanned file already scanned files identified known e.g. vt default sha256 hash without uploading complete files sha256 query url form codice_1 file uploads normally limited 128 mb 2017 virustotal discontinued support windows uploader several browser extensions available vtzilla mozilla firefox vtchromizer google chrome vtexplorer internet explorer allow user download files directly virustotal web application prior storing computer well scanning urls service also offers android app employs public api search installed application virustotal previously scanned ones show status application previously scanned submitted api key must provided restrictions public api usage may apply see public api virustotal provides free service public api allows automation online features upload scan files submit scan urls access finished scan reports make automatic comments urls samples restrictions apply requests made public api requiring individual api key freely obtained online signing low priority scan queue limited number requests per time frame etc antivirus engines used detection uploading files. ref name= files/url /ref antivirus scanning engines used url scanning utilities used provide additional info uploaded files files uploaded virustotal may shared freely anti-malware companies also retained store virustotal page states virustotal confidentiality files urls sent virustotal shared antivirus vendors security companies help improving services products believe eventually lead safer internet better end-user protection default file/url submitted virustotal detected least one scanner freely sent scanners detect resource additionally files urls enter private store may accessed premium mainly security/antimalware companies/organizations virustotal users improve security products services
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Computer security
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open source cluster application resources open source cluster application resources oscar linux-based software installation high-performance cluster computing oscar allows users install beowulf type high performance computing cluster
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Distributed computing architecture
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code42 code42 american software company develops markets crashplan backup software services suite code42 started project create facebook-like desktop application ended focusing online storage element released crashplan 2007 company raised 52.5 million 2012 consumers use crashplan small business plan requires monthly subscription backup cloud plans larger enterprises also available crashplan initially got positive reviews pricing feature-set user interface large initial backups reported slow august 2017 original home plans discontinued business-focused plans remaining options code42 founded consulting company 2001 matthew dornquast brian bispala mitch coopet company name honors douglas adams authored hitchhiker ’ guide galaxy died year book number 42 answer ultimate question life universe everything code42 first projects included redesign sun country airlines ’ website 2002 project retailer target corporation ticket booking engine midwest airlines income services business used fund product ideas six years 2006 company planned create facebook-like desktop application project became large impractical code42 focused online storage element application creating crashplan 2007 june 2011 code42 acquired minneapolis-based mobile development company recursive awesome llc support software mobile devices recursive ’ employees moved minneapolis headquarters later 10,000 square-foot expansion offices built 2012 code42 raised 52.5 million funding funding first distribution 100 million pool established 2011 accel partners fund big data companies mid 2015 former eloqua ceo joe payne succeeded co-founder matthew dornquast ceo company raised additional 85 million funding october 2015 august 22 2017 code42 announced shutting crashplan home october 2018 accepting new subscriptions would maintain existing subscriptions end existing subscription period point backups would purged old home plans replaced former pro plans business-focused although still possible use private purposes backups friends/family supported new product company explained shift business strategy focus exclusively enterprise small business segments two great options continue getting best backup solution. code42 ranked leader backup software recent g2 crowd backup survey summer 2017 april 2011 80 code42 software ’ revenue comes business customers remainder comes consumers small portion service provider partners code42 profitable year since founded grew 1.4 million revenue 2008 11.46 million 2010 18.5 million 2011 2012 company backed 100 petabytes data processed 100 billion files day code42 best known developing marketing crashplan data backup service crashplan backs data remote servers hard drives backup computers longer supported available mac windows linux also crashplan pro proe mobile apps accessing backed-up data ios android windows devices initial backups may take several hours via lan days internet depending amount data bandwidth available afterwards continuous incremental backups conducted without user intervention used paid option seed loading hard drive sent user faster local backup could performed drive could shipped back code42 initial backup however seeded backup service longer available around beginning 2016 neither corresponding restore-to-door service would allow hard drive containing extensive restore data backups shipped back user faster over-the-internet download data encrypted password-protected stored proprietary format also option secure private key corporate users crashplan proe back private servers instead code42 data centers four five cases software option create private on-site backup server code42 used develop market file sharing service called shareplan released october 2013 according star tribune competed dropbox shareplan used pin access files track users october 2014 revision software added features regulatory compliance like sarbanes-oxley options private public hybrid cloud deployment single login crashplan using feature called code42 edge platform improved december 2014 two-factor authentication features shareplan discontinued august 2015 22 august 2017 code42 stopped offering new subscriptions consumers focusing business plans code42 also stopped renewals existing customers comparative review published wall street journal geoffrey fowler observed crashplan favorite four services evaluated observed lacked fine print whereas services charged additional fees basic features n't really unlimited pc magazine gave crashplan 4.5 5 stars awarded editor choice review praised user interface local backup options security features said mobile explorer-based features limited product review macworld gave crashplan rating 4.5 5 gartner gave enterprise version crashplan proe excellent rating techworld praised crashplan operating system support configuration options ars technica said crashplan better features pricing options competitors
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Computer security
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synchronous serial communication synchronous serial communication describes serial communication protocol data sent continuous stream constant rate synchronous communication requires clocks transmitting receiving devices synchronized – running rate – receiver sample signal time intervals used transmitter start stop bits required reason synchronous communication permits information passed circuit per unit time asynchronous serial communication time transmitting receiving clocks tend drift apart requiring resynchronization early synchronous protocols byte-oriented protocols synchronization maintained transmitting sequence synchronous idle characters line actively transmitting data transparently within long transmission block certain number idles sent prior transmission ibm binary synchronous protocol bisync still use examples byte-oriented protocols ibm synchronous transmit-receive str digital data communications message protocol ddcmp digital equipment corporation computer manufacturers often offered similar protocols differing mainly small details bit-oriented protocols synchronous protocols view transmitted data stream bits semantics meaning control codes defined terms bit sequences instead characters synchronization maintained idle line transmitting predefined sequence bits synchronous data link control sdlc specifies station continue transmitting sequence 1 bits idle line data transmitted idle line prefixed special bit sequence '01111110 b called flag sdlc first bit-oriented protocol developed later adopted international organization standardization iso high-level data link control hdlc examples bit-oriented protocols logical link control llc —ieee 802.2 ansi advanced data communication control procedures adccp
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Internet protocols
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ice lake microprocessor ice lake intel codename 10th generation intel core processors based new sunny cove microarchitecture ice lake expected replace coffee lake whiskey lake kaby lake cannon lake microarchitectures 2019 2020 representing architecture step intel process-architecture-optimization model ice lake produced second generation intel 10 nm process 10 nm+ becoming intel second microarchitecture manufactured 10 nm process following limited launch cannon lake 2018 ice lake designed intel israel processor design team haifa israel expected ice lake in-silicon mitigations certain meltdown spectre hardware vulnerabilities intel released details ice lake intel architecture day december 2018 stating sunny cove core ice lake would focusing single-thread performance new instructions scalability improvements intel stated performance improvements would achieved making core deeper wider smarter core ice lake built sunny cove features 50 increase size l1 data cache larger l2 cache size product dependent larger μop cache larger 2nd level tlb core also increased width increasing execution ports 8 10 doubling l1 store bandwidth allocation width also increased 4 5 paging table main memory supports linear address space 57 bits physical address space 52 bits increasing theoretical addressable memory space 4 pb 64 tb ice lake features intel gen11 graphics increasing number execution units eus 64 24 48 gen9.5 graphics achieving 1 tflops compute performance eu supports 7 threads meaning design 512 concurrent pipelines feeding eus 3 mb l3 cache 4x increase gen9.5 alongside increased memory bandwidth enabled lpddr4x low-power mobile platforms gen11 graphics also introduces tile-based rendering coarse pixel shading cps intel implementation variable-rate shading vrs architecture also includes all-new hevc encoder design august 1 2019 intel released specifications icelake u cpus cpus lost suffix m3 naming instead intel uses trailing zero indicate power package 9w pre-orders laptops featuring ice lake cpus started august 2019 shipment expected september
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Computer architecture
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small small small machine algol like language programming language developed dr. nevil brownlee auckland university aim language enable people write algol-like code ran small machine also included string type easier text manipulation small used extensively 1980 1985 auckland university programming teaching aid internal projects originally written run burroughs corporation b6700 main frame fortran iv subsequently rewritten small ported dec pdp-10 architecture operating system tops-10 ibm s360 architecture operating system vm/cms 1985 small object-oriented features added handle structures missing early language formalise file manipulation operations
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Programming language topics
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stan software stan probabilistic programming language statistical inference written c++ stan language used specify bayesian statistical model imperative program calculating log probability density function stan licensed new bsd license stan named honour stanislaw ulam pioneer monte carlo method stan created andrew gelman bob carpenter development team consisting 34 members stan accessed several interfaces stan implements gradient-based markov chain monte carlo mcmc algorithms bayesian inference stochastic gradient-based variational bayesian methods approximate bayesian inference gradient-based optimization penalized maximum likelihood estimation stan implements reverse-mode automatic differentiation calculate gradients model required hmc nuts l-bfgs bfgs variational inference automatic differentiation within stan used outside probabilistic programming language stan used fields including social science pharmaceutical statistics market research medical imaging
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Programming language topics
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copperheados copperheados source-available operating system smartphones tablet computers based android mobile platform adds privacy security features official releases android open source project google goal upstreaming back android linux openbsd august 2016 copperheados announced future versions operating system based android nougat 7.x would released no-commercial-usage license funding could acquired march 2017 support pixel pixel xl devices launched offer buy devices copperheados preinstalled june 11th 2018 daniel micay main developer copperheados then-chief technology officer 50 stakeholder company announced publicly cut company e-mail sent james donaldson order turn access subreddit micay twitter account mr. donaldson representing company let micay know micay would receive pay signed employment agreement twitter micay wrote mr. donaldson attempting seize micay personal gpg key also used secure key parts copperhead project micay reportedly deleted signing keys required release updates copperheados following list devices supported copperheados past following devices supported
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Operating systems
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linc 4gl linc logic information network compiler fourth-generation programming language used mostly unisys computer systems linc originally developed short-cut template two programmers reproduce automate production computer applications different companies similar requirements specifications requirements similar companies followed common generic business model businesses dealt commodities parts suppliers customers named components linc terminology manufactured assembled purchased sold actions termed events linc terminology components events interface specifications ispecs contained database definitions screen designs business rules application system lirc logic information report compiler part linc developed allow programmer produce reports e.g purchase orders invoices credit notes consignment notes bills sale information reports accessed using various user-defined views components events called profiles reports run separate task separate thread execution could also written run background process could put sleep period time woken perform processing put sleep part reason introduction new terminology make system easier programmers isolated lot underlying technology similarly different names intentionally used control structures do.when rather loop look.up determine rather read open close statements generated automatically allowed linc make programmers much efficient application systems produced easier read maintain differentiated simply yet another third generation high level language linc assumption use total reliance facilities available packaged burroughs computer written operating system job control language cobol programming language database management system network definition user terminal etc see also history version 11 character changed linc lirc specifications previously held source-code files held database designed developed using linc 4gl subject rigorous automatic validation new linc-based system specifications stored named linc interactive linc development environment lde extensive reliance terminal screen painting i.e mocking -up crt data-entry screen used assist system definition e.g define component database attributes name length alpha numeric validation rules etc. defining report layouts early 1990s new pc-based tool developing linc specifications released linc development assistant lda lda written mixture smalltalk c++ rather linc 4gl latter intended run personal computer version 17 intended development done lda linc known unisys enterprise application environment eae generate cobol code burroughs sperry mainframes microsoft windows various unix linux platforms also generate gui front-end clients addition compiling generated code deploying databases correspond specification databases supported include burroughs dmsii sperry rdms oracle database microsoft sql server recent update unisys replacing eae unisys agile business suite ab suite ldl language promoted ldl+ new object-oriented features development environment makes use microsoft visual studio ide model driven approach extended uml based class diagram integrated source code solution way round trip update achieved changes business rules result changes uml representation vice versa ab suite 4.0 makes use visual studio 2012 integrates team foundation server 2012 ab suite generates either .net environment clearpath mcp environment ab suite developer write less code traditional c java environment linc originally developed two new zealand computer programmers gil simpson peter hoskins working saudi arabia early 1980s first developed exclusively operation single model burroughs computer system comprising totally integrated system etc linc system created 3rd gl cobol application dmsii database definition ndlii network description wfl job control source code job control statements subsequently run compile elements create integrated system database applications user terminal network burroughs purchased rights sell product 1982 product development retained original inventors early requirement extend product use burroughs mid-range large scale computing platforms burroughs merged sperry corporation form unisys language extended used sperry univac 1100/2200 series machines also subsequently new zealand development centre set christchurch gil simpson develop product ownership later transferred unisys product mainframe computer centre resources transitioned unisys acus australian centre unisys software sydney australia gil simpsons christchurch team went create jade language/database could import run linc code commodity hardware linc supported following platforms development work acus unisys transitioned acus indian outsourcing operation early 2008 eventually product sold 4,000 clients worldwide principally linc fails compete myriad turnkey systems readily available many sources especially ibm cost purchasing customising existing product e.g hogan retail banking system perceived less expensive/risk using linc create scratch entire business system rules weaknesses arise mostly dependence basis burroughs dms cobol differ greatly computing platforms
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Programming language topics
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let encrypt let encrypt non-profit certificate authority run internet security research group isrg provides x.509 certificates transport layer security tls encryption charge certificate valid 90 days renewal take place time offer accompanied automated process designed overcome manual creation validation signing installation renewal certificates secure websites launched april 12 2016 project claims goal make encrypted connections world wide web servers ubiquitous eliminating payment web server configuration validation email management certificate renewal tasks meant significantly lower complexity setting maintaining tls encryption linux web server execution two commands sufficient set https encryption acquire install certificates end software package included official debian ubuntu software repositories current initiatives major browser developers mozilla google deprecate unencrypted http counting availability let encrypt project acknowledged potential accomplish encrypted connections default case entire web service issues domain-validated certificates since fully automated organization validation extended validation certificates require human validation registrants therefore offered let encrypt transparent possible hope protect trustworthiness guard attacks manipulation attempts purpose regularly publish transparency reports publicly log acme transactions e.g using certificate transparency use open standards free software much possible support acme v2 wildcard certificates added march 2018 let encrypt service provided internet security research group isrg public benefit organization major sponsors electronic frontier foundation eff mozilla foundation ovh cisco systems facebook google chrome internet society partners include certificate authority identrust university michigan u-m stanford law school linux foundation well stephen kent raytheon/bbn technologies alex polvi coreos june 2015 let encrypt announced generation first rsa root certificate isrg root x1 root certificate used sign two intermediate certificates also cross-signed certificate authority identrust one intermediate certificates used sign issued certificates kept offline backup case problems first intermediate certificate identrust certificate preinstalled major web browsers let encrypt certificates normally validated accepted upon installation even browser vendors include isrg root certificate trust anchor let encrypt developers planned generate ecdsa root certificate well later 2015 pushed back early 2016 2019 challenge–response protocol used automate enrolling certificate authority called automated certificate management environment acme involves various requests web server domain covered certificate based whether resulting responses match expectations control enrollee domain assured domain validation order acme client software sets special tls server server system gets queried acme certificate authority server special requests using server name indication domain validation using server name indication dvsni validation processes run multiple times separate network paths checking dns entries provisioned done multiple geographically diverse locations make dns spoofing attacks harder acme interactions based exchanging json documents https connections draft specification available github version submitted internet engineering task force ietf proposal internet standard certificate authority consists piece software called boulder written go implements server side acme protocol published free software source code terms version 2 mozilla public license mpl provides restful api accessed tls-encrypted channel apache-licensed python certificate management program called certbot formerly letsencrypt gets installed client side web server enrollee used order certificate conduct domain validation process install certificate configure https encryption http server later regularly renew certificate installation agreeing user license executing single command enough get valid certificate installed additional options like ocsp stapling http strict transport security hsts also enabled automatic setup initially works apache nginx let encrypt issues certificates valid 90 days reason given certificates limit damage key compromise mis-issuance encourage automation official certbot client third-party clients allow automation certificate renewal several third-party client implementations several languages created community let encrypt project started 2012 two mozilla employees josh aas eric rescorla together peter eckersley electronic frontier foundation j. alex halderman university michigan internet security research group company behind let encrypt incorporated may 2013 let encrypt announced publicly november 18 2014 january 28 2015 acme protocol officially submitted ietf standardisation april 9 2015 isrg linux foundation declared collaboration root intermediate certificates generated beginning june june 16 2015 final launch schedule service announced first certificate expected issued sometime week july 27 2015 followed limited issuance period test security scalability general availability service originally planned begin sometime week september 14 2015 august 7 2015 launch schedule amended provide time ensuring system security stability first certificate issued week september 7 2015 followed general availability week november 16 2015 cross-signature identrust planned available let encrypt opens public september 14 2015 let encrypt issued first certificate domain day isrg submitted root program applications mozilla microsoft google apple october 19 2015 intermediate certificates became cross-signed identrust causing certificates issued let encrypt trusted major browsers november 12 2015 let encrypt announced general availability would pushed back first public beta would commence december 3 2015 public beta ran december 3 2015 april 12 2016 3.8 million unexpired unrevoked active certificates cover 7 million unique domains part due support large hosting companies
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Computer security
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azure stream analytics microsoft azure stream analytics serverless scalable complex event processing engine microsoft enables users develop run real-time analytics multiple streams data sources devices sensors web sites social media applications users set alerts detect anomalies predict trends trigger necessary workflows certain conditions observed make data available downstream applications services presentation archiving analysis users author real-time analytics using simple declarative sql-like language embedded support temporal logic callouts custom code javascript user defined functions extend streaming logic written sql callouts azure machine learning helps predictive scoring streaming data azure stream analytics serverless job service azure eliminates need infrastructure servers virtual machines managed clusters users processing used running jobs azure stream analytics integrates azure iot hub enable real-time analytics data iot devices applications users build real-time dashboards power bi live command control view real-time dashboards help transform live data actionable insightful visuals stream analytics supports three different types input sources azure event hubs azure iot hubs azure blob storage additionally stream analytics supports azure blob storage input reference data help augment fast moving event data streams static data stream analytics supports wide variety output targets support power bi allows real-time dashboarding event hub service bus topics queues help trigger downstream workflows support azure table storage azure sql databases azure sql data warehouse azure sql document db azure data lake store enable variety downstream analysis archiving capabilities
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Distributed computing architecture
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kaspersky anti-virus kaspersky anti-virus antivirus kasperskovo formerly known antiviral toolkit pro often referred kav antivirus program developed kaspersky lab designed protect users malware primarily designed computers running microsoft windows macos although version linux available business consumers kaspersky anti-virus features include real-time protection detection removal viruses trojans worms spyware adware keyloggers malicious tools auto-dialers well detection removal rootkits also includes instantaneous automatic updates via kaspersky security network service microsoft windows users may download antivirus rescue disk scans host computer booting inside isolated linux environment addition kaspersky anti-virus prevents disabled malware without user permission via password access prompts upon disabling protection elements changing internal settings also scans incoming instant messenger traffic email traffic automatically disables links known malware hosting sites using internet explorer firefox includes free technical support free product upgrades within paid-subscription periods kaspersky anti-virus lacks certain features found kaspersky internet security missing features include personal firewall hips secure keyboard antispam antibanner parental control tools also kaspersky like majority competitors incompatible many anti-virus anti-spyware software 2005 two critical flaws discovered kaspersky anti-virus one could let attackers commandeer systems use one allowed chm files insert malicious code edition kaspersky anti-virus solution linux workstations available business consumers offers many features included mainstream version windows including on-access on-demand scanners specialized editions kaspersky anti-virus also available variety linux servers offer protection forms malware newly released macintosh capable edition kaspersky anti-virus compatible intel processor based mac os x tiger higher include brand new version mac os x snow leopard released august 2009 kaspersky lab internal testing concludes consuming 2 cpu impact performance designed maintain user friendly mac-like interface mac users familiar kaspersky anti-virus mac contains definitions detect block malware affecting windows linux macos alike kaspersky anti-virus mac also scans shared folders users running windows using virtual pc capable apple macintosh personal computers dvd-rom cd-rom drive internet explorer 8 windows installed 3.0 also required installation kaspersky anti-virus windows latest version either downloaded official website purchased retail according av-comparatives kaspersky anti-virus rates highly amongst virus scanners terms detection rates malware removal even despite fact program failed two virus bulletin tests 2007 another two 2008 example latest malware removal test done av-comparatives kaspersky antivirus 2013 awarded highest advanced+ rating able successfully remove 14 malware samples used test following file detection test kaspersky antivirus 2013 also able achieve advanced+ rating 99.2 sample detection rate addition pc world awarded kaspersky anti-virus 6 highest rank 2007 anti-virus comparative well-known highly regarded ars technica lists kaspersky one best choices anti-virus windows platform kaspersky anti-virus a-listed uk pc journal pc pro late 2007 scored highly detection removal malware pc pro attributes “ combination software ’ heuristic scanning uncompromising approach database updates many packages check new virus signatures daily basis kaspersky runs hourly schedule improving chances immunized infection reaches it. ” march 2015 bloomberg accused kaspersky close ties russian military intelligence officials kaspersky slammed claims blog calling coverage sensationalist guilty exploiting paranoia increase readership indicate whether claims true june 2015 united states national security agency united kingdom government communications headquarters said nsa gchq agents broke kaspersky antivirus software could spy people leaks indicate
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Computer security
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monitor mode monitor mode rfmon radio frequency monitor mode allows computer wireless network interface controller wnic monitor traffic received wireless channel unlike promiscuous mode also used packet sniffing monitor mode allows packets captured without associate access point ad hoc network first monitor mode applies wireless networks promiscuous mode used wired wireless networks monitor mode one eight modes 802.11 wireless cards operate master acting access point managed client also known station ad hoc repeater mesh wi-fi direct tdls monitor mode uses monitor mode include geographical packet analysis observing widespread traffic acquiring knowledge wi-fi technology hands-on experience especially useful auditing unsecure channels protected wep monitor mode also used help design wi-fi networks given area channel number wi-fi devices currently used discovered helps create better wi-fi network reduces interference wi-fi devices choosing least used wi-fi channels software kismac kismet combination packet analyzers read pcap files provide user interface passive wireless network monitoring usually wireless adapter unable transmit monitor mode restricted single wireless channel though dependent wireless adapter driver firmware features chipset also monitor mode adapter check see cyclic redundancy check crc values correct packets captured captured packets may corrupted microsoft windows network driver interface specification ndis api supported extensions monitor mode since ndis version 6 first available windows vista ndis 6 supports exposing 802.11 frames upper protocol levels previous versions exposed fake ethernet frames translated 802.11 frames monitor mode support ndis 6 optional feature may may implemented client adapter driver implementation details compliance ndis specifications vary vendor vendor many cases monitor mode support properly implemented vendor example ralink drivers report incorrect dbm readings realtek drivers include trailing 4-byte crc values versions windows prior windows vista packet analyzer applications wildpackets omnipeek tamosoft commview wifi provide device drivers support monitor mode linux interfaces 802.11 drivers support monitor mode many drivers offer support sta drivers ralink broadcom every manufacturer ’ provided driver ’ support monitor mode freebsd netbsd openbsd dragonfly bsd also provide interface 802.11 drivers supports monitor mode many drivers operating systems support monitor mode well mac os x 10.4 later releases drivers airport extreme network adapters allow adapter put monitor mode libpcap 1.0.0 later provides api select monitor mode capturing operating systems
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Computer security
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mixter mixter computer security specialist mixter first made transition computer underground large-scale public awareness 2000 time newspapers magazines worldwide mentioned link massively destructive effective distributed denial service ddos attacks crippled shut major websites including yahoo buy.com ebay amazon e-trade msn.com dell zdnet cnn early reports stated fbi-led national infrastructure protection center nipc questioning mixter regarding tool called stacheldraht barbed wire although mixter suspect tool tribal flood network tfn update called tfn2k ultimately discovered ones used attacks causing estimated 1.7 billion usd damages 2002 mixter returned public eye author hacktivismo six/four system six/four system censorship resistant network proxy works using trusted peers relay network connections ssl encrypted links example distribution includes program act web proxy connections hidden reach far end trusted peer
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Computer security
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finisterrae finisterrae 100th supercomputer top500 ranking november 2007 running 12.97 teraflops would rank position 258 list june 2008 also third powerful supercomputer spain marenostrum magerit located galicia project promoted xunta de galicia regional government galicia spanish national research council csic founded 1993 serve platform foster scientific innovation invest research development estimated base project completed 2010 expected reach top10 powerful supercomputers world reaches full capacity supercomputer physically hosted cesga main finisterrae characteristics depicted following table one special characteristics supercomputer ratio cores ram one reason received denomination singular technical scientific installation spanish government denomination given installations value makes singular way installations include canary island grand telescope alba synchrotron even third fastest supercomputer spain projects require special amounts memory held first second supercomputer therefore must executed finisterrae finisterrae supercomputer located cesga integrated system shared-memory nodes smp numa architecture finisterrae composed 144 computational nodes hierarchic storing system main purpose aim supercomputer research supercomputer mainly used three universities located galicia universidade da coruña universidade de santiago de compostela universidade de vigo well research organizations like csic main projects held supercomputer divided four fields
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Distributed computing architecture
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domain-specific multimodeling domain-specific multimodeling software development paradigm view made explicit separate domain-specific language dsl successful development modern enterprise system requires convergence multiple views business analysts domain experts interaction designers database experts developers different kinds expertise take part process building system different work products must managed aligned integrated produce running system every participant development process particular language tailored solve problems specific view system challenge integrating different views avoiding potential cacophony multiple different languages coordination problem domain-specific multimodeling promising compared traditional development paradigms single-language programming general-purpose modeling reap benefits new paradigm must solve coordination problem problem also known fragmentation problem context global model management one proposal solve problem coordination method three-step method overcome obstacles integrating different views coordinating multiple languages method prescribes 1 identify 2 specify references across language boundaries overlaps different languages finally method offers concrete proposals 3 apply knowledge actual development form consistency navigation guidance enterprise systems based multiple domain-specific languages abundant languages metamodel defined extensible markup language xml enjoy particularly widespread adoption illustrate development multiple languages draw example case study apache open business ofbiz system briefly stated ofbiz enterprise resource planning system includes standard components inventory accounting e-commerce etc components implemented mixture xml-based languages regular java code example let us focus content management component particularly use case administrative user creates online web survey shown screenshot refer example create survey example figure shows screenshot administrative interface content management application running ofbiz instance create survey user fills fields input form hits update button creates new survey edited later published frontend website ofbiz behind scenes use case involves several artifacts written different languages example let us focus three languages entity service form dsl three languages correspond roughly structural behavioural user interface concern ofbiz entity dsl used describe underlying data model hence way created survey saved service dsl used describe interface service invoked user hits update button finally form dsl used describe visual appearance form although three languages tailored different things separated entirely user interface invokes certain application logic application logic manipulates data application example non-orthogonal concerns languages overlap concerns represent separated entirely let us examine three languages bottom-up manner point overlaps entity dsl defines structure data ofbiz listing shows definition survey entity business object represents concept survey code listing self-explanatory entity called survey defined 10 fields field name type field surveyid used primary key definition loaded central component ofbiz called entity engine entity engine instantiates corresponding business object purpose entity engine manage transactional properties business objects interact various persistence mechanisms java database connectivity enterprise javabeans even legacy system service dsl specifies interface services ofbiz service encapsulates part application logic system purpose language uniform abstraction various implementing mechanisms individual services implemented java scripting language using rule engine listing shows interface createsurvey service apart name service element specifies location invocation command implementation service default-entity-name attribute specifies service refers survey entity defined previous listing overlap two languages specifically so-called soft reference model service dsl refers model entity dsl reference used two auto-attributes elements specify input output service form typed attributes input service accepts attributes corresponding non-primary key nonpk fields survey entity attributes optional output service returns attributes corresponding primary key pk fields survey i.e. case surveyid field attributes mandatory purpose reference across languages case reduce redundancy attributes createsurvey service corresponds fields survey entity therefore necessary specify form dsl used describe layout visual appearance input forms user interface language consists domain concepts form field listing shows implementation editsurvey form time form dsl overlaps service dsl target attribute form alt-target elements specify input submission form directed either updatesurvey createsurvey services auto-fields-service element specifies form include field corresponding attributes updatesurvey service similar attributes createsurvey service produces similar effect importing definitions another model case auto-attributes elements previous listing see possible customize appearance imported fields isanonymous finally submitbutton added localized title user submit data referenced service create survey example described implemented using models three different languages complete implementation actually involves even languages screen dsl specify layout screen form placed minilang dsl data-manipulation language used implement service however three languages illustrate main idea making concern concrete example also shows simple way reducing redundancy letting languages overlap slightly domain-specific languages like described limited expressiveness often necessary add code snippets general-purpose language like java implement specialized functionality beyond scope languages method called multi-level customization since method commonly used setups multiple languages illustrate continuation example let us call build pdf example suppose want build pdf file survey response online surveys users create building pdf file outside scope languages need write java code invoke third-party pdf library perform specialized functionality two artifacts required first additional service model shown service dsl defines interface concrete service accessed modeling level service model describes location implementation input output attributes second need code snippet shown contains actual implementation service service multiple inputs outputs input java method map called context argument names argument values returns output form another map called results multi-level customization method uses soft references similar create survey example main difference reference model code rather model model advantage case third-party java library building pdfs leveraged another typical application use java code snippets invoke external webservices import results suitable format example illustrates advantages using multiple languages development however also difficulties associated kind development difficulties stem observation kinds artifacts introduce process coordination developer efforts needed refer difficulties coordination problem coordination problem conceptual technical aspect conceptually main problem understand different languages interaction properly design coordinate models multiple languages developers must sufficient understanding languages interact technically main problem enforce consistency tools must provided detect inconsistencies early i.e. modeling time assist developers resolving inconsistencies following examine two aspects greater detail first problem developers encounter starting development multiple languages language cacophony learning different languages understanding interaction necessary make sense complex composition artifacts ofbiz framework instance seventeen different languages 200 000 lines domain-specific language code complexity quite overwhelming currently established method characterizing different languages developers quickly reach operational understanding tools important ad hoc mechanism learning exploration developers typically use tools learn experiments especially three areas tools domain-specific models helpful first understanding language difficult case xml-based domain-specific languages frequent intuitive objection syntax matters objection argument stated following way “ different languages hard understand add confusion xml-based syntax particularly verbose unintelligible using single general-purpose language like java would better developers could rely syntax already know ” objection certainly important misses central point xml similar representation format may syntax developers actually work one advantages using xml-based domain-specific languages provide domain-specific editors figure shows hypothetical editor entity dsl might look like editor presents domain simple visually appealing manner may well use xml representation perhaps layout configuration underneath may complain xml bad choice could also object general-purpose language like java poor choice tasks furthermore developers may feel less intimidated editor figure code listings xml java accept syntax matters use different languages tailored editors becomes reasonable strategy simplicity editor makes language easier understand hence easier use words syntax matters objection may reason explore field domain-specific languages second language interactions reveal relations languages developers able jump related elements different artifacts ease navigation different software artifacts important criterion tools traditional development environments although performed empirical studies area hypothesize proper navigation facilities increase productivity claim supported observation major development environments today offer quite sophisticated navigation facilities type hierarchy browser ability quickly locate jump references method definition development environments provide navigation facilities maintain continuously updated model sourcefiles form abstract syntax tree development environment multiple languages navigation much difficult existing environments geared parsing representing dsl models abstract syntax trees arbitrary perhaps even application-specific languages languages previous example furthermore without internal representation existing environments resolve neither intra- inter-language references languages hence provide useful navigation means developers must maintain conceptual model parts system related new tools navigation facilities geared multiple languages would hand helpful understanding relations languages terms create survey example tools display relations three languages using soft references navigation points third understand language use must able distinguish correct editing operations wrong ones development environment traditional development environments long provided guidance writing program incremental compilation allows environment offer detailed suggestions developer complete statement intrusive kinds guidance also exist syntax-oriented editors input conforming grammar entered generic text-editors parameterized grammar language existed long time existing editors take inter-language consistency relations account providing guidance previous example ideal editor instance able suggest createsurvey service valid value developer edits target attribute form definition environment could reason artifacts different languages would also able help developer identify program states local global consistency situation arise model well-formed hence locally consistent time violates inter-language constraint guidance intelligent assistance form proposals complete model would useful setups multiple languages complex consistency constraints tool-suggested editing operations could make easier developer get started process learning use languages technical aspect coordination problem essentially matter enforcing consistency detect inconsistencies across models multiple languages modeling time fully understand complexity consistency requirements system based multiple languages useful refine concept consistency consistency either intra- inter-consistency intra-consistency concerns consistency elements within single model requirements model must conform metamodel i.e. syntactically well-formed terms create survey example entity model must instance conform xsd schema entity dsl schema metamodel entity dsl specifies elements composed extent valid domains attributes inter-consistency achieved references across language boundaries resolved kind consistency subdivided 1 model-to-model consistency 2 model-to-code consistency model-to-model consistency concerns referential integrity well high-level constraints system create survey example default-entity-name attribute service listing refers name attribute entity listing change one values without updating break reference high-level consistency constraints across different models also exist discussed later project certain patterns conventions naming relating model elements current development environments must tailored specific languages handwritten plugins similar mechanisms order enforce consistency languages previous example model-to-code consistency essential requirement multi-level customization models supplemented code snippets build pdf example necessary check models code actually fit partly matter making sure soft references models code broken similar referential integrity model-to-model consistency also matter making sure code violate expectations set model build pdf example model specifies outbytewrapper always part output i.e. outbytewrapper key put results map analysis code shows outbytewrapper part output exceptions thrown line 10 words possible executions code violate specification modeling level generally state multi-level customization imposes fine-grained constraints involved models code snippets coordination problem arises fact multiple languages used single system two previous subsections illustrate problem conceptual side well low-level technical side challenges described real rather hypothetical challenges specifically faced challenges two concrete representative case studies enterprise resource planning system ofbiz health care system district health information system dhis cases medium-sized systems actual industrial use solution practical problems encountered work systems set guidelines prototypes following introduce overall conceptual framework incorporates guidelines prototypes coherent method coordination method goal coordination method solve coordination problem thereby provide better support development multiple languages properly appreciate method important understand prescribe design individual languages plenty methods tools already proposed method assumes existence setup multiple domain-specific languages given setup one apply method method consists three steps shown diagram step consist couple parts shown little boxes diagram boxes dotted lines represent automatic processes boxes solid lines represent manual ones following explain steps bit detail goal identification step identify language overlaps described example overlap area concerns two languages intersect soft references form dsl service dsl service dsl entity dsl create survey use case examples overlaps another example case customized code snippet used extend model overlaps frequent expressiveness general-purpose languages needed implement specialized requirements beyond scope model identification step either manual automatic process depending complexity overlaps overlaps identified made explicit information used input second step method specification step goal specification step create coordination model specifies languages interact references across language boundaries system constitute coordination model particular system created mapping main software artifacts common representation additional information domain- application-specific constraints may also encoded provide rich representation coordination model based generic information language grammars constraints well application-specific information concrete models application-specific constraints means even though languages used across several products product specification unique coordination model coordination model used basis various forms reasoning final step method application step goal application step take advantage coordination model coordination model allows tools derive three layers useful information first coordination model used enforce consistency across multiple languages coordination model specifies consistency relations elements different languages refer tools enforce referential integrity perform static checks final system deployment second consistency relations used navigate visualize map web different languages development setup information used quickly link relate elements different languages provide traceability among different models third based consistency relations navigational information elements related tools provide guidance specifically completion assistance model completion instance provided generic manner across domain-specific tools coordination method best seen conceptual framework prescribes certain workflow working multiple languages three successive steps constitute workflow supported integrated workbench development environment focus rather extending developer existing environments add support 1 identification 2 specification 3 application main advantage approach developers actually tested work given us feedback kind evaluation method valuable reduces risk solving purely hypothetical problem several papers introduce different steps coordination method report evaluation elaborates technical aspects individual experiment overall results promising significant number errors found production systems given rise constructive dialog developers future tool requirements development process based guidelines supported tools constitutes serious attempt solve coordination problem make domain-specific multimodeling practical proposition
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Programming language topics
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gnu guix gnu guix cross-platform package manager tool instantiate manage operating system unix-like operating systems based nix package manager guile scheme apis specializes providing exclusively free software differing traditional package managers guix like nix utilizes purely functional deployment model software installed unique directories generated cryptographic hashes dependencies software included within hash solving problem dependency hell approach package management promises generate reliable reproducible portable packages guix packages defined functional guile scheme apis specifically designed package management dependencies tracked directly language special values called derivations evaluated guix daemon lazily guix keeps track references automatically installed packages garbage collected package depends cost greater storage requirements upgrades guix guaranteed atomic efficiently rolled back also enables multiple users safely install software system without administrator privileges extra storage requirements translates greater bandwidth usage binary substitutes downloaded compared distributions debian user chooses build everything source even larger storage space bandwidth required development gnu guix intertwined guix system guix 1.0 guix system distribution short guixsd complete installable gnu system using linux-libre kernel gnu shepherd init system roll-back feature guix inherited design nix found popular linux distributions debian derivatives arch linux derivatives major distributions fedora centos opensuse project coordinated internet team volunteers incorporated french non-profit guix europe members community features related package management features guix see features guix system inherited design nix content package manager kept directory /gnu/store guix daemon write access achieved via specialised bind mounts store file system mounted read prohibiting interference even root user guix daemon remounts store read/writable private namespace guix talks daemon build things fetch substitutes kept store guix like nix built garbage collection facilities help prune dead store items keep live ones example package definition hello-package written using guile package recipes easily inspected running e.g guix edit hello changed guix making system transparent easily hackable inherited design nix manipulation store items independent directories store begin base32 encoded hash contents dependencies item guix package uses profiles generations collection symlinks specific store items together comprising user installed profile every time package installed removed new generation built e.g profile user installed gnu hello contains links store item holds version hello installed currently used guix e.g version c087a90e06d7b9451f802323e24deb1862a21e0f guix corresponds following item /gnu/store/md2plii4g5sk66wg9cgwc964l3xwhrm9-hello-2.10 built recipe addition symlinks profile guix builds also contains union info-manuals man-pages icons fonts etc user browse documentation access icons fonts installed default symlinks profile generations stored /var/guix filesystem user create number profiles invoking guix package -p profile-name command new directory profile-name well profile-generation-symlinks created current directory guix package enables instantaneous roll-back previous profile generation via changing symlink earlier profile generation profiles also stored store e.g item profile containing hello /gnu/store/b4wipjlsapvnijmbawl7sh76087vpl4n-profile built activated running guix install hello guix environment enables user easily enter environment necessary packages development software present without clogging users default profile dependencies multiple projects e.g running guix environment hello enters throw-away environment everything needed compile hello guix present gcc guile etc. want persistent gc-rooted environment garbage collected next run guix gc create root e.g running guix environment -- root=hello-root hello enters environment everything needed compile guix present gcc guile etc registered root current directory symlinking items store guix pack enables user bundle together store items output docker binary image relocatable tarball squashfs binary guix pack enables user view different graphs packages dependencies guix system distribution abbreviated guixsd linux distribution built around gnu guix package manager enables declarative operating system configuration allows reliable system upgrades easily rolled back uses linux-libre kernel support gnu hurd kernel development february 3 2015 distribution added free software foundation list free linux distributions following cpu architectures supported ia-32 x64 aarch32 aarch64 april 2019 work progress power9 support system services core feature guix system enables user declaratively compose configuration daemons background services easily specify relevant configurations enables user within single configuration file declare whole os e.g tor proxy sshd server webserver serving guix-web via nginx specific port bootup system services ricardo wurmus one maintainers explains extendability like services defined using guile scheme list services continue grow 1.0.0 list services includes following guixsd uses gnu daemon shepherd init system developed tandem guix written guile well previously known dmd stood daemon managing daemons daemons-managing daemon changed names avoid collision digital mars compiler shepherd supplies user-space functionality asynchronously services shepherd generic functions object data types exported use shepherd extend base operating system defined way contrast systemd userspace shepherd process runs user core shepherd model user space initialisation concept extension form composability services designed layered onto services augmenting elaborate specialised behaviours desired expresses instantiation-based dependency relationships found many modern init systems making system modular also allows services interact variadically services arbitrary ways shepherd also provides so-called virtual services allow dynamic dispatch class related service objects instantiate mail transfer agent mta system system governed via shepherd daemon represent user space directed acyclic graph system-service − responsible early phases boot init − root subsequently initialised services extensions system-service functionality either directly transitively services written configured guile scheme gnu shepherd intended highly programmable system administrator also used manage per-user profiles unprivileged daemons services services configuration stored uniformly object-oriented scheme code core set services provided basic guix system distribution arbitrary new services flexibly declared guile object system goops existing services redefined user discretion asking shepherd dynamically rewrite services specified ways instantiation gnu shepherd originally designed work gnu hurd later adopted guixsd guixsd date unstable development git repository shared guix enables users organizations set stable release channels via channel-feature packages guix generally up-to-date thanks lack package maintainer bottleneck anyone contribute update subject community approval process assisted tools guix refresh changes git repository peer-reviewed community members committed one 45 people commit access practice sometimes builds cause system breakages users typo similar error often solved within minutes way guix pull operates means users retain working system meantime system update leave users broken system users easily roll back individual packages well whole system state means stable channel common linux distributions longer needed users willing report bug wait minutes trying update via guix pull gnu project announced november 2012 first release gnu guix functional package manager based nix provides among things guile scheme apis project started june 2012 ludovic courtès one gnu guile hackers august 20 2015 announced guix ported gnu hurd project fixed release schedule released approximately every 6 months jesse smith distrowatch weekly reviewed guixsd 0.15.0 said guixsd package manager like criticized limited hardware support limited documentation
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Operating systems
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visitor pattern object-oriented programming software engineering visitor design pattern way separating algorithm object structure operates practical result separation ability add new operations existing object structures without modifying structures one way follow open/closed principle essence visitor allows adding new virtual functions family classes without modifying classes instead visitor class created implements appropriate specializations virtual function visitor takes instance reference input implements goal double dispatch visitor design pattern one twenty-three well-known gof design patterns describe solve recurring design problems design flexible reusable object-oriented software objects easier implement change test reuse problems visitor design pattern solve new operations needed frequently object structure consists many unrelated classes inflexible add new subclasses time new operation required .. distributing operations across various node classes leads system hard understand maintain change solution visitor design pattern describe makes possible create new operations independently classes object structure adding new visitor objects see also uml class sequence diagram gang four defines visitor nature visitor makes ideal pattern plug public apis thus allowing clients perform operations class using visiting class without modify source moving operations visitor classes beneficial drawback pattern however makes extensions class hierarchy difficult new classes typically require new codice_1 method added visitor consider design 2d computer-aided design cad system core several types represent basic geometric shapes like circles lines arcs entities ordered layers top type hierarchy drawing simply list layers plus added properties fundamental operation type hierarchy saving drawing system native file format first glance may seem acceptable add local save methods types hierarchy also useful able save drawings file formats adding ever methods saving many different file formats soon clutters relatively pure original geometric data structure naive way solve would maintain separate functions file format save function would take drawing input traverse encode specific file format done added different format duplication functions accumulates example saving circle shape raster format requires similar code matter specific raster form used different primitive shapes case primitive shapes like lines polygons similar thus code becomes large outer loop traversing objects large decision tree inside loop querying type object another problem approach easy miss shape one savers new primitive shape introduced save routine implemented one file type others leading code extension maintenance problems instead visitor pattern applied encodes logical operation whole hierarchy one class containing one method per type cad example save function would implemented separate visitor subclass would remove duplication type checks traversal steps would also make compiler complain shape omitted another motive reuse iteration code example iterating directory structure could implemented visitor pattern would allow creating file searches file backups directory removal etc. implementing visitor function reusing iteration code uml class diagram codice_2 class n't implement new operation directly instead codice_2 implements dispatching operation codice_4 dispatches delegates request accepted visitor object codice_5 codice_6 class implements operation codice_7 br codice_8 implements codice_4 dispatching codice_10 codice_6 class implements operation codice_12 uml sequence diagram shows run-time interactions codice_13 object traverses elements object structure codice_14 calls codice_4 element br first codice_13 calls codice_4 codice_2 calls codice_19 accepted codice_20 object element codice_21 passed codice_20 visit codice_2 call codice_24 br thereafter codice_13 calls codice_4 codice_8 calls codice_28 codice_20 visits codice_8 calls codice_31 visitor pattern requires programming language supports single dispatch common object-oriented languages c++ java smalltalk objective-c swift javascript python c condition consider two objects class type one termed element visitor visitor declares codice_1 method takes element argument class element concrete visitors derived visitor class implement codice_1 methods implements part algorithm operating object structure state algorithm maintained locally concrete visitor class element declares codice_34 method accept visitor taking visitor argument concrete elements derived element class implement codice_34 method simplest form call visitor ’ codice_1 method composite elements maintain list child objects typically iterate calling child ’ codice_34 method client creates object structure directly indirectly instantiates concrete visitors operation performed implemented using visitor pattern calls codice_34 method top-level element codice_34 method called program implementation chosen based dynamic type element static type visitor associated codice_1 method called implementation chosen based dynamic type visitor static type element known within implementation codice_34 method dynamic type element bonus visitor ca n't handle argument given element type compiler catch error thus implementation codice_1 method chosen based dynamic type element dynamic type visitor effectively implements double dispatch languages whose object systems support multiple dispatch single dispatch common lisp c via dynamic language runtime dlr implementation visitor pattern greatly simplified a.k.a dynamic visitor allowing use simple function overloading cover cases visited dynamic visitor provided operates public data conforms open/closed principle since modify extant structures single responsibility principle since implements visitor pattern separate component way one algorithm written traverse graph elements many different kinds operations performed traversal supplying different kinds visitors interact elements based dynamic types elements visitors example shows print tree representing numeric expression involving literals addition example presented using classic dynamic language runtime implementations classic visitor print operations type implemented one expressionprinter class number overloads visit method namespace wikipedia example declares separate codice_43 class takes care printing expression classes must expose members make possible namespace wikipedia case object responsibility know print stream visitor object stream syntax creating class classes created sending messages classes writestream subclass expressionprinter expressionprinter » write anobject object subclass expression expression subclass literal literal class » avalue literal » value avalue literal » puton astream expression subclass addition addition class » left right b addition » left anexpression addition » right anexpression addition » puton astream object subclass program program » main class abstractdispatcher // forward declare abstractdispatcher class file // parent class elements archivedfile splitfile // forward declare specific elements files dispatched class archivedfile class splitfile class extractedfile class abstractdispatcher // declares interface dispatcher class archivedfile public file // specific element class 1 class splitfile public file // specific element class 2 class extractedfile public file // specific element class 3 class dispatcher public abstractdispatcher // implements dispatching int main package visitor2 import fmt type visitor interface type element interface type wheel struct func self *wheel accept visitor visitor string func self *wheel getname string func self *engine accept visitor visitor string func self *body accept visitor visitor string type car struct func self *car accept visitor visitor string func self *visitcar visit element element string package visitor import func testvistor *testing.t visiting engine visiting body visiting front left wheel visiting front right wheel visiting back left wheel visiting back right wheel following example language java shows contents tree nodes case describing components car printed instead creating codice_44 methods node subclass codice_45 codice_46 codice_47 codice_48 one visitor class codice_49 performs required printing action different node subclasses require slightly different actions print properly codice_49 dispatches actions based class argument passed codice_1 method codice_52 analogous save operation different file format likewise import java.util.list interface carelement interface carelementvisitor class wheel implements carelement class body implements carelement class engine implements carelement class car implements carelement class carelementdovisitor implements carelementvisitor class carelementprintvisitor implements carelementvisitor public class visitordemo flexible approach pattern create wrapper class implementing interface defining accept method wrapper contains reference pointing codice_53 could initialized constructor approach avoids implement interface element see article java tip 98 article elements initarg elements defmethod do-something object other-object defmethod do-something object wheel other-object integer defmethod do-something object wheel other-object symbol let make-instance 'auto codice_54 parameter superfluous codice_55 reason possible use anonymous function calls desired target method lexically captured object defmethod traverse function auto other-object removed multiple dispatch occurs call issued body anonymous function codice_55 mapping function distributes function application elements object thus traces visitor pattern disappear except mapping function evidence two objects involved knowledge two objects dispatch types lambda function python support method overloading visit methods different model types need different names visitor pattern example abc import abcmeta abstractmethod not_implemented implement class carelement class body carelement class engine carelement class wheel carelement class car carelement class carelementvisitor class carelementdovisitor carelementvisitor class carelementprintvisitor carelementvisitor car car car.accept carelementprintvisitor car.accept carelementdovisitor visiting front left wheel visiting front right wheel visiting back left wheel visiting back right wheel visiting body visiting engine visiting car kicking front left wheel kicking front right wheel kicking back left wheel kicking back right wheel moving body starting engine starting car one using python 3 make general implementation accept method class visitable one could extend iterate class method resolution order would like fall back already-implemented classes could also use subclass hook feature define lookup advance
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Programming language topics
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self-stabilization self-stabilization concept fault-tolerance distributed computing distributed system self-stabilizing end correct state matter state initialized correct state reached finite number execution steps first glance guarantee self stabilization may seem less promising traditional fault-tolerance algorithms aim guarantee system always remains correct state certain kinds state transitions however traditional fault tolerance always achieved example achieved system started incorrect state corrupted intruder moreover complexity hard debug analyze distributed systems hence hard prevent distributed system reaching incorrect state indeed forms self-stabilization incorporated many modern computer telecommunications networks since gives ability cope faults foreseen design algorithm many years seminal paper edsger dijkstra 1974 concept remains important presents important foundation self-managing computer systems fault-tolerant systems result dijkstra paper received 2002 acm podc influential-paper award one highest recognitions distributed computing community moreover dijkstra death award renamed called dijkstra award e.w dijkstra 1974 presented concept self-stabilization prompting research area demonstration involved presentation self-stabilizing mutual exclusion algorithms also showed first self-stabilizing algorithms rely strong assumptions system previous protocols used practice actually stabilize assuming existence clock global system assuming known upper bound duration system transition ten years later leslie lamport pointed importance dijkstra work 1983 conference called symposium principles distributed computing researchers directed attention elegant fault-tolerance concept talk lamport stated regard dijkstra brilliant work least brilliant published paper almost completely unknown regard milestone work fault tolerance ... regard self-stabilization important concept fault tolerance fertile field research.afterwards dijkstra work awarded acm-popdc influential paper award became acm association computing machinery dijkstra prize distributed computing given annual acm-popdc symposium distributed algorithm self-stabilizing starting arbitrary state guaranteed converge legitimate state remain legitimate set states thereafter state legitimate starting state algorithm satisfies specification property self-stabilization enables distributed algorithm recover transient fault regardless nature moreover self-stabilizing algorithm initialized eventually starts behave correctly regardless initial state dijkstra paper introduces concept self-stabilization presents example context token ring — network computers ordered circle computer processor see whole state one processor immediately precedes state may imply processor token token one requirements exactly one must hold token given time second requirement prescribes node passes token computer/processor succeeding token eventually circulates ring first self-stabilizing algorithms detect errors explicitly order subsequently repair instead constantly pushed system towards legitimate state since traditional methods detecting error often difficult time-consuming behavior considered desirable method described paper cited collects huge amount information whole network one place attempts determine whether collected global state correct even determination alone hard task recently researchers presented newer methods light-weight error detection self-stabilizing systems using local checking term local refers part computer network local detection used computer network required communicate entire network order detect error — error detected computer communicate nearest neighbors local detection methods simplified task designing self-stabilizing algorithms considerably error detection mechanism recovery mechanism designed separately newer algorithms based detection methods also turned much efficient moreover papers suggested rather efficient general transformers transform non self stabilizing algorithms become self stabilizing idea combination 4 parts self stabilizing initial self stabilizing protocols also presented papers efficient reset protocols presented later e.g additional efficiency introduced notion time-adaptive protocols idea behind small number errors occurs recovery time made short dijkstra original self-stabilization algorithms property useful property self-stabilizing algorithms composed layers layers exhibit circular dependencies stabilization time composition bounded sum individual stabilization times layer new approaches dijkstra work emerged later case krzysztof apt ehsan shoja proposition demonstrated self-stabilization naturally formulated using standard concepts strategic games particularly concept improvement path particular work sought demonstrate link self-stabilization game theory time complexity self-stabilizing algorithm measured asynchronous rounds cycles measure output stabilization time subset state variables defined externally visible output certain states outputs defined correct legitimate set outputs components system said stabilized time starts correct provided stays correct indefinitely unless additional faults occur output stabilization time time number asynchronous rounds output stabilizes system self-stabilizing system said randomized self-stabilizing self-stabilizing expected number rounds needed reach correct state bounded constant formula_1 design self-stabilization above-mentioned sense well known difficult job fact class distributed algorithms property local checking legitimacy network state evaluated single process obvious case dijkstra token-ring defined process detect whether network state legitimate case one token present non-neighboring processes suggests self-stabilization distributed system sort collective intelligence component taking local actions based local knowledge eventually guarantees global convergence end help overcome difficulty designing self-stabilization defined types stabilization devised instance weak stabilization property distributed system possibility reach legitimate behavior every possible state weak stabilization easier design guarantees possibility convergence runs distributed system rather convergence every run self-stabilizing algorithm silent converges global state values communication registers used algorithm remain fixed extension concept self-stabilization superstabilization intent cope dynamic distributed systems undergo topological changes classical self-stabilization theory arbitrary changes viewed errors guarantees given system stabilized superstabilizing systems passage predicate always satisfied system topology reconfigured
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Computer architecture
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xacml xacml stands extensible access control markup language standard defines declarative fine-grained attribute-based access control policy language architecture processing model describing evaluate access requests according rules defined policies published standard specification one goals xacml promote common terminology interoperability access control implementations multiple vendors xacml primarily attribute-based access control system abac attributes bits data associated user action resource inputs decision whether given user may access given resource particular way role-based access control rbac also implemented xacml specialization abac xacml model supports encourages separation access decision point use access decisions baked client applications based local machine userids access control lists acls difficult update decision criteria governing policy changes client decoupled access decision authorization policies updated fly affect clients immediately version 1.0 ratified oasis standards organization 2003 version 2.0 ratified oasis standards organization february 1 2005 first committee specification xacml 3.0 released august 10 2010 latest version xacml 3.0 standardized january 2013 non-normative terminology following rfc 2904 except pap xacml structured 3 levels elements policy set contain number policy elements policy set elements policy contain number rule elements policies policy sets rules requests use subjects resources environments actions xacml provides target basically set simplified conditions subject resource action must met policy set policy rule apply given request policy policy set found apply given request rules evaluated determine access decision response addition way check applicability target information also provides way index policies useful need store many policies quickly sift find ones apply request access service arrives pdp know look policies might apply request policies indexed based target constraints note target may also specify applies request policy set policy rule contain target elements conditions exist rules conditions essentially advanced form target use broader range functions importantly used compare two attributes together e.g subject-id==doctor-id conditions possible implement segregation duty checks relationship-based access control within xacml concept called obligations used obligation directive policy decision point pdp policy enforcement point pep must carried access approved pep unable comply directive approved access may must realized augmentation obligations eliminates gap formal requirements policy enforcement example obligation could look like access control rule xacml obligation effective way meet formal requirements non-repudiation example hard implement access control rules furthermore formal requirements part access control policy obligations separate functions makes policies consistent centralization environment easier achieve happens xacml two rules policies contradict imagine instance first rule would say managers view documents second rule would say one work 9am request alice trying view document 8am rule wins combining algorithms tell us help resolve conflicts xacml defines number combining algorithms identified rulecombiningalgid policycombiningalgid attribute policy policyset elements respectively rule-combining algorithm defines procedure arriving access decision given individual results evaluation set rules similarly policy-combining algorithm defines procedure arriving access decision given individual results evaluation set policies list higher order functions listed formal definition refer xacml standard http //docs.oasis-open.org/xacml/3.0/xacml-core-v3-schema-wd-17.xsd xacml 3.0 introduces administrative delegation json profile xacml request/response rest profile xacml multiple decision profile xacml many implementation delegation new xacml 3.0 delegation mechanism used support decentralized administration access policies allows authority delegator delegate parts authority someone else authority another user delegate without need involve modification root policy delegation model delegation rights separated access rights instead referred administrative control policies access control administrative policies work together following scenario partnership companies many services protected access control system system implements following central rules protect resources allow delegation access control rules administration control rules consultant enters corporation delegation issued locally consultant supervisor authorizing consultant access systems directly delegator supervisor scenario may right delegate limited set access rights consultants new features xacml 3.0 listed http //www.webfarmr.eu/2010/07/enhancements-and-new-features-in-xacml-3-axiomatics/ xacml tc also publishing list changes http //wiki.oasis-open.org/xacml/differencesbetweenxacml2.0andxacml3.0 rule implements use-it-lose-it access control paradigm user log 30 days lose access pseudo-code deny currentdatetime lastlogin 30 days rule grants access current time greater 9am less 5pm following contains obligation block obligations statements returned along decision enrich decision flow example pep must log access granted 2013 2014 xacml technical committee focused designing new profiles facilitate developer integration include three profiles showcased cloud identity summit 2014 monterey california using profiles integrating fine-grained authorization applications becomes much easier json profile xacml simplifies integration pep pdp saml identity sso federation standard used authentication saml used common identity token format different applications saml xacml defined oasis saml xacml designed interoperate saml used carry identity information virtual identities xacml used drive access control logic policies oauth 2.0 considered authorization standard differs xacml though origin purpose applications oauth xacml handle user approval delegated access password management xacml simply provides xacml oauth combined together deliver comprehensive approach authorization
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Computer security
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isyvmon isyvmon computer system network monitoring software application system created it-cube systems designed monitor track status various applications network services servers network hardware isyvmon based open source software nagios centreon licensed gnu gpl v3 special features development isyvmon „ full discovery anh “ freeware enterprise edition auto discovery adi also available freeware edition introduced connection splunk www.splunk.com isyvmon isyvmon first world open public release isyvmon first official release idea isyvmon born introduced based 2007 created standardized toolkit evaluated relevant available monitoring tools nagios interface handling unhandy
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Computer security
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execute place computer science execute place xip method executing programs directly long term storage rather copying ram extension using shared memory reduce total amount memory required general effect program text consumes writable memory saving dynamic data instances program run single copy work several criteria met storage requirements usually met using flash memory addressed individual words read operations although bit slower normal system ram setups typically first stage boot loader xip program linked run address flash chip mapped power-up contains minimal program set system ram depends components used individual boards generalized enough proper sequence could embedded processor hardware loads second stage bootloader os kernel ram initialization writable memory may available computations performed within processor registers reason first stage boot loaders tend written assembler language minimum provide normal execution environment next program processors either embed small amount sram chip allow using onboard cache memory ram make first stage boot loader easier write using high-level language kernel bootloader address space generally assigned internally order use xip sufficient instruct linker place unmodifiable modifiable data different address ranges provide mechanism modifiable data copied writable memory code run assumes data accessed normally done part previous stage within small code segment beginning program address space assigned externally application program run system provide virtual memory compiler needs access modifiable data adding offset pointer private copy data area case external loader responsible setting instance specific memory areas xip places requirements file systems often difficult meet systems without page table entire file must stored within consecutive bytes must fragmented flash based file systems often aim distribute data sectors flash chip least erase cycles even wear chip prolonging lifetime complications speed tradeoff mean xip generally used first stage bootloaders memory extremely short supply relatively new file system linux called axfs advanced xip file system aims overcome shortcomings associated xip especially regard in-place execution user-space applications makes instance possible split executable binary file xip regions thus avoiding restriction fragmentation mentioned netbsd implementation also development
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Computer file systems
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hypervideo hypervideo hyperlinked video displayed video stream contains embedded interactive anchors allowing navigation video hypermedia elements hypervideo thus analogous hypertext allows reader click word one document retrieve information another document another place document hypervideo combines video non-linear information structure allowing user make choices based content video user interests crucial difference hypervideo hypertext element time text normally static video necessarily dynamic content video changes time consequently hypervideo different technical aesthetics rhetorical requirements static hypertext page example hypervideo might involve creation link object video visible certain duration therefore necessary segment video appropriately add metadata required link frames—or even objects—in video pertinent information media forms kinoautomat 1967 world first interactive movie modern hypervideo systems implements core concepts movie non linear narrative interactivity video-to-video linking demonstrated interactive cinema group mit media lab elastic charles hypermedia journal developed 1988 1989 annotations called micons placed inside video indicating links content implementing interactive kon-tiki museum listol used order represent video footnotes video footnotes deliberate extension literary footnote applied annotating video thereby providing continuity traditional text early hypervideo 1993 hirata et al considered media based navigation hypermedia systems type media used query media retrieved example part image defined shape color example could link related image approach content video becomes basis forming links related content hotvideo implementation kind hypervideo developed ibm china research laboratory 1996 navigation associated resources accomplished clicking dynamic object video 1997 project mit media lab object-based media group called hypersoap developed concept short soap opera program viewer could click enhanced remote control objects video find information could purchased company watchpoint media formed order commercialize technology involved resulting product called storyteller oriented towards interactive television illustrating progression hypervideo hypertext storyspace hypertext writing environment employs spatial metaphor displaying links utilizes 'writing spaces generic containers content link writing spaces 1996 hypercafe popular experimental prototype hypervideo made use tool create narrative video spaces developed early model hypervideo system placing users virtual cafe user dynamically interacts video follow different conversations 1997 israeli software firm ephyx technologies released product called v-active one first commercial object based authoring system hypervideo technology success though ephyx changed name veon 1999 time shifted focus away hypervideo provision development tools web broadband content.. eline technologies founded 1999 developed hypervideo solutions called videoclix today videoclix used saas software service solution distribute monetize clickable video web mobile devices advantage videos play back popular video players quicktime flash well multiple online video platforms brightcove theplatform ooyala videoclix also offers technology integrated 3rd party players based quicktime flash mpeg-4 html5 first steps hypervideo taken late 1980s would appear hypervideo taking unexpectedly long realize potential many experiments hypercafe hypersoap extensively followed authoring tools moment available small number providers amount video content increases becomes available possibilities linking video increase even faster digital libraries constantly growing video important part news outlets amassed vast video archives could useful education historical research direct searching pictures videos much harder task indexing searching text could greatly facilitated hypervideo methods hypervideo challenging compared hyperlinked text due unique difficulty video presents node segmentation separating video algorithmically identifiable linkable content video basic time sequence images turn simply two dimensional arrays color information order segment video meaningful pieces objects images scenes within videos necessary provide context space time extract meaningful elements image sequence humans naturally able perform task desirable algorithmically developing method achieve however complex problem ntsc frame rate 30 frames per second even short video 30 seconds comprises 900 frames identification distinct video elements would tedious human intervention required every frame moderate amounts video material manual segmentation clearly unrealistic standpoint time smallest unit video single frame node segmentation could performed frame level—a straightforward task frame easily identifiable however single frame contain video information since videos necessarily dynamic analogously single word separated text convey meaning thus necessary consider scene next level temporal organization scene defined minimum sequential set frames conveys meaning important concept hypervideo one might wish hypervideo link active throughout one scene though next scene granularity therefore natural creation hypervideo consequently hypervideo requires algorithms capable detecting scene transitions one imagine coarser levels temporal organization scenes grouped together form narrative sequence turn grouped form video point view node segmentation however concepts critical even frame smallest time unit one still spatially segment video sub-frame level separating frame image constituent objects necessary performing node segmentation object level time introduces complexity case also even object differentiated one frame usually necessary follow object sequence frames process known object tracking essential creation links objects videos spatial segmentation object achieved example use intensity gradients detect edges color histograms match regions motion detection combination methods required nodes segmented combined associated linking information metadata must incorporated original video playback metadata placed conceptually layers tracks top video layered structure presented user viewing interaction thus display technology hypervideo player neglected creating hypervideo content example efficiency gained storing geometry areas associated tracked objects certain keyframes allowing player interpolate keyframes developed hotvideo furthermore creators videoclix emphasize fact content plays back standard players quicktime flash one considers flash player alone installed 98 internet-enabled desktops mature markets perhaps reason success product current arena user replies video content traditionally form text image links embedded playback sequence video allowed video hosting services viddler become embedded within imagery video within portions playback via selected time lengths inside progress slider element feature become known video comments audio comments perhaps significant consequence hypervideo result commercial advertising devising business model monetize video proven notoriously difficult application traditional advertising methods—for example introducing ads video—is likely rejected online community revenue selling advertising video sharing sites far promising hypervideo offers alternate way monetize video allowing possibility creating video clips objects link advertising e-commerce sites provide information particular products new model advertising less intrusive displaying advertising information user makes choice clicking object video since user requested product information type advertising better targeted likely effective
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Web technology
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algaebase algaebase global species database information groups algae well one group flowering plants sea-grasses algaebase evolved michael guiry seaweed website grown database algae throughout world freshwater terrestrial brackish well marine habitats 2005 database contained 65,000 names september 2006 122,240 species infraspecific names database 5,826 images 38,290 bibliographic items 138,706 distributional records currently data marine algae particularly seaweeds complete 30,000 species algae included rhodophyta 6000 species marine chlorophyta 1500 species phaeophyceae 1755 species complete diatoms smaller freshwater green algae currently august 2010 incomplete groups programming carried visualid http //www.visualid.com pier kuipers caoilte guiry compilation data funded irish government department education science prtli 3 4 programmes http //www.hea.ie/en/prtli
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Databases
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trinoo trinoo trin00 set computer programs conduct ddos attack believed trinoo networks set thousands systems internet compromised remote buffer overrun exploits first suspected trinoo attacks described cert incident note 99-04 trinoo network connected february 2000 distributed denial service attack yahoo website trinoo famous allowing attackers leave message folder called cry_baby file self replicating modified regular basis long port 80 active trinoo authored teenager new orleans went alias phifli attacker using compromised host compiles list machines compromised process done automatically compromised host host stores mount information including find hosts compromise soon list machines compromised compiled scripts run compromise convert trinoo masters daemons one master control multiple daemons daemons compromised hosts launch actual udp floods victim machine ddos attack launched attacker issues command master hosts masters instruct every daemon start dos attack ip address specified command many doss comprise ddos attack
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Computer security
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interrupt vector table interrupt vector table ivt data structure associates list interrupt handlers list interrupt requests table interrupt vectors entry interrupt vector table called interrupt vector address interrupt handler concept common across processor architectures ivts may implemented architecture-specific fashions example dispatch table one method implementing interrupt vector table processors interrupt vector table including chips intel amd infineon microchip atmel nxp etc interrupt vector table used three popular methods finding starting address interrupt service routine predefined method loads program counter pc directly address entry inside interrupt vector table jump table contains executable code principle extremely short interrupt handler could stored entirely inside interrupt vector table practice code entry single jump instruction jumps full interrupt service routine isr interrupt intel 8080 atmel avr 8051 microchip microcontrollers use predefined approach fetch method loads pc indirectly using address entry inside interrupt vector table pull address table loading pc address every entry ivt address interrupt service routine motorola/freescale microcontrollers use fetch method interrupt acknowledge method external device gives cpu interrupt handler number interrupt acknowledge method used intel pentium many older microprocessors cpu affected interrupt looks interrupt handler interrupt vector table transfers control
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Computer architecture
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exit control lock exit control lock also known exit control device exit lock simply exit control prevents deters unauthorized exit exit control locks often used retail establishments deter shoplifting also used airports controlled areas people held clear customs quarantine stations exit control locks also used libraries one well-staffed entrance exit number exits intended emergency use exit control devices often used hospitals interfaced wireless sensors worn newborn children exits lock baby stolen one hospital rooms often shops make exit emergency use deter shoplifting usually door locked emergency exit button next pushing emergency exit button unlock door set shop fire alarm deters shoplifting person unlocks door order take item building emergency may reported police cctv footage available many exit control locks based magnetic locks one type delayed egress magnetic locks allow door open immediately allows guard get door door opens also release fire alarm power failure otherwise locks hold exit doors shut units common alzheimer units exit control systems include request exit detector pushbutton opens exit exit requests enabled facilities entrances well exits require authentication swiping otherwise reading card card reader intruder slips entrance controls building able detained questioning
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Computer security
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inotify inotify inode notify linux kernel subsystem acts extend filesystems notice changes filesystem report changes applications replaces earlier facility dnotify similar goals inotify created john mccutchan merged linux kernel mainline kernel version 2.6.13 released august 29 2005 later kernel versions included improvements required library interfaces added gnu c library glibc version 2.4 released march 2006 support inotify completed glibc version 2.5 released september 2006 one major use desktop search utilities like beagle functionality permits reindexing changed files without scanning filesystem changes every minutes would inefficient inotify also used automatically update directory views reload configuration files log changes backup synchronize upload limitations imposed inotify include following number advantages using inotify compared older dnotify api replaced dnotify program use one file descriptor directory monitoring become bottleneck since limit file descriptors per process could reached later fanotify created overcome issue use file descriptors along dnotify also proved problem using removable media devices could unmounted since file descriptors kept resource busy another drawback dnotify level granularity since programmers monitor changes directory level access detailed information environmental changes occur notification message sent stat structure must used considered necessary evil cache stat structures maintained every new stat structure generated comparison run cached one inotify api uses fewer file descriptors allowing programmers use established select poll interface rather signal notification system used dnotify also makes integration existing select- poll-based libraries like glib easier
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Operating systems
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second normal form second normal form 2nf normal form used database normalization 2nf originally defined e.f. codd 1971 relation second normal form fulfills following two requirements 2 non-prime attribute functionally dependent proper subset candidate key relation non-prime attribute relation attribute part candidate key relation put simply relation 2nf 1nf every non-prime attribute relation dependent whole every candidate key note put restriction non-prime non-prime attribute dependency addressed third normal form functional dependency part candidate key violation 2nf addition primary key relation may contain candidate keys necessary establish non-prime attributes part-key dependencies candidate keys following relation satisfy 2nf multiple manufacturer country dependent part candidate key even designer specified primary key model full name relation 2nf candidate keys manufacturer model also candidate key manufacturer country dependent proper subset manufacturer make design conform 2nf necessary two relations
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Databases
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ipad 2018 ipad officially sixth-generation ipad 9.7-inch 25cm tablet computer designed developed marketed apple inc announced march 27 2018 education-focused event lane tech high school chicago successor 2017 model upgraded apple a10 fusion soc support styluses apple pencil ipad also marketed towards educators schools ipad priced starting us 329 consumers 309 educators/students 299 schools ipad shipped ios 11.3 iwork suite apps preinstalled included apple pencil stylus support ipad hardware nearly identical previous generation except upgrades apple pencil stylus support upgraded processor apple a10 fusion available three colors silver space gray new gold color match updated color introduced iphone 8 ipad 2 gigabytes ram 7.5mm thick ipad available 32 128 gb storage options unlike ipad pro ipad feature laminated display gareth beavis techradar praised addition apple pencil powerful a10 chip noted costly previous generation ipad scott stein cnet also praised addition support apple pencil upgrade a10 chip criticized lacking smart connector well display technology ipad pro writing 2018 entry-level ipad n't add much makes already excellent tablet better buy ever
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Operating systems
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third normal form third normal form 3nf normal form used normalizing database design reduce duplication data ensure referential integrity ensuring 1 entity second normal form 2 non-prime non-key attribute transitively dependent key i.e non-prime attribute depends non-prime attributes non-prime attributes must depend keys 3nf designed eliminate undesirable data anomalies reduce need restructuring time make data model informative make data model neutral different kinds query statistics codd later realized 3nf achieve first goals developed boyce-codd normal form address limitations 3nf third normal form 3nf normal form used database normalization 3nf originally defined e.f. codd 1971 codd definition states table 3nf following conditions hold non-prime attribute r attribute belong candidate key r. transitive dependency functional dependency x → z x determines z indirectly virtue x → → z case → x 3nf definition equivalent codd expressed differently given carlo zaniolo 1982 definition states table 3nf functional dependencies x → least one following conditions holds zaniolo definition gives clear sense difference 3nf stringent boyce–codd normal form bcnf bcnf simply eliminates third alternative every element a-x set difference x prime attribute approximation codd definition 3nf paralleling traditional pledge give true evidence court law given bill kent every non-key attribute must provide fact key whole key nothing key common variation supplements definition oath help codd requiring existence key ensures table 1nf requiring non-key attributes dependent whole key ensures 2nf requiring non-key attributes dependent nothing key ensures 3nf phrase useful mnemonic fact mentions single key means defines necessary sufficient conditions satisfy 2nd 3rd normal forms 2nf 3nf concerned equally candidate keys table one key chris date refers kent summary intuitively attractive characterization 3nf notes slight adaptation may serve definition slightly stronger boyce–codd normal form attribute must represent fact key whole key nothing key 3nf version definition weaker date bcnf variation former concerned ensuring non-key attributes dependent keys prime attributes keys parts keys must functionally dependent represent fact key sense providing part key rule applies functionally dependent attributes applying attributes would implicitly prohibit composite candidate keys since part key would violate whole key clause example 2nf table fails meet requirements 3nf row table needs tell us particular tournament particular year composite key tournament year minimal set attributes guaranteed uniquely identify row tournament year candidate key table breach 3nf occurs non-prime attribute winner date birth transitively dependent candidate key tournament year via non-prime attribute winner fact winner date birth functionally dependent winner makes table vulnerable logical inconsistencies nothing stop person shown different dates birth different records order express facts without violating 3nf necessary split table two update anomalies occur tables unlike winner primary key second table thus allowing one value date birth winner relation always decomposed third normal form relation r rewritten projections r ... r whose join equal original relation decomposition lose functional dependency sense every functional dependency r derived functional dependencies hold projections r ... r. decomposition computed polynomial time definition 3nf offered carlo zaniolo 1982 given proven following way let x → nontrivial fd i.e one x contain let non-key attribute also let key r. → x 3nf tables free update insertion deletion anomalies certain types 3nf tables rarely met practice affected anomalies tables either fall short boyce–codd normal form bcnf meet bcnf fall short higher normal forms 4nf 5nf 3nf ideal machine processing segmented nature data model difficult consume human user analytics via query reporting dashboards often facilitated different type data model provided pre-calculated analysis trend lines period-to-date calculations month-to-date quarter-to-date year-to-date cumulative calculations basic statistics average standard deviation moving averages previous period comparisons year ago month ago week ago e.g dimensional modeling beyond dimensional modeling flattening stars via hadoop data science
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Databases
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fourth normal form fourth normal form 4nf normal form used database normalization introduced ronald fagin 1977 4nf next level normalization boyce–codd normal form bcnf whereas second third boyce–codd normal forms concerned functional dependencies 4nf concerned general type dependency known multivalued dependency table 4nf every one non-trivial multivalued dependencies x formula_1 x superkey—that x either candidate key superset thereof column headings relational database table divided three disjoint groupings x z context particular row refer data beneath group headings x z respectively multivalued dependency x formula_1 signifies choose x actually occurring table call choice x compile list xyz combinations occur table find x associated entries regardless z essentially presence z provides useful information constrain possible values trivial multivalued dependency x formula_1 one either subset x x together form whole set attributes relation functional dependency special case multivalued dependency functional dependency x → every x determines exactly one never one consider following example row indicates given restaurant deliver given variety pizza given area table non-key attributes key restaurant pizza variety delivery area therefore meets normal forms bcnf assume however pizza varieties offered restaurant affected delivery area i.e restaurant offers pizza varieties makes areas supplies meet 4nf problem table features two non-trivial multivalued dependencies restaurant attribute superkey dependencies non-trivial multivalued dependencies non-superkey reflect fact varieties pizza restaurant offers independent areas restaurant delivers state affairs leads redundancy table example told three times a1 pizza offers stuffed crust a1 pizza starts producing cheese crust pizzas need add multiple rows one a1 pizza delivery areas moreover nothing prevent us incorrectly might add cheese crust rows one a1 pizza delivery areas thereby failing respect multivalued dependency restaurant formula_1 pizza variety eliminate possibility anomalies must place facts varieties offered different table facts delivery areas yielding two tables 4nf contrast pizza varieties offered restaurant sometimes legitimately vary one delivery area another original three-column table would satisfy 4nf ronald fagin demonstrated always possible achieve 4nf rissanen theorem also applicable multivalued dependencies 1992 paper margaret s. wu notes teaching database normalization typically stops short 4nf perhaps belief tables violating 4nf meeting lower normal forms rarely encountered business applications belief may accurate however wu reports study forty organizational databases 20 contained one tables violated 4nf meeting lower normal forms rare situations 4nf table conform higher normal form 5nf situations complex real-world constraint governing valid combinations attribute values 4nf table implicit structure table
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Databases
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first normal form first normal form 1nf property relation relational database relation first normal form domain attribute contains atomic indivisible values value attribute contains single value domain first definition term 1971 conference paper edgar codd defined relation first normal form none domains sets elements first normal form essential property relation relational database database normalization process representing database terms relations standard normal forms first normal minimal requirement first normal form enforces criteria following scenarios first illustrate database design might violate first normal form followed examples comply table stores names telephone numbers customers one requirement though retain telephone numbers customers simplest way satisfying requirement allow telephone number column given row contain one value note telephone number column simply contains text numbers different formats importantly one number two customers duplicating related information column would satisfied arbitrary text would fine arbitrary text obviously intended column contain telephone number seen telephone numbers text atomic subdivided well seen telephone numbers text contains one number two rows representation telephone numbers first normal form columns contain non-atomic values contain one apparent solution introduce columns technically table violate requirement values atomic however informally two telephone number columns still form repeating group repeat conceptually attribute namely telephone number arbitrary hence meaningless ordering introduced 555-861-2025 put telephone number1 column rather telephone number2 column reason customers could two telephone numbers many telephone number n columns possible search telephone number without searching arbitrary number columns adding extra telephone number may require table reorganized addition new column rather new row tuple added null value telephone number2 customer 789 also issue bring model first normal form split strings used hold telephone number information atomic i.e indivisible entities single phone numbers ensure row contains one phone number note id longer unique solution duplicated customers uniquely identify row need use combination id telephone number value combination unique although column separately contains repeated values able uniquely identify row tuple requirement 1nf alternative design uses two tables columns contain one telephone number design instead customer-to-telephone number link appears row using customer id key one-to-many relationship exists name number tables row parent table customer name associated many telephone number rows child table customer telephone number telephone number belongs one one customer worth noting design meets additional requirements second third normal form edgar f. codd definition 1nf makes reference concept 'atomicity codd states values domains relation defined required atomic respect dbms codd defines atomic value one decomposed smaller pieces dbms excluding certain special functions meaning column divided parts one kind data one part means dbms depends another part column hugh darwen chris date suggested codd concept atomic value ambiguous ambiguity led widespread confusion 1nf understood particular notion value decomposed problematic would seem imply data types atomic date suggests notion atomicity absolute meaning value may considered atomic purposes may considered assemblage basic elements purposes position accepted 1nf defined reference atomicity columns conceivable data type string types numeric types array types table types acceptable 1nf table—although perhaps always desirable example would desirable separate customer name column two separate columns first name surname according date definition table first normal form isomorphic relation means specifically satisfies following five conditions violation conditions would mean table strictly relational therefore first normal form examples tables views would meet definition first normal form first normal form defined chris date permits relation-valued attributes tables within tables date argues relation-valued attributes means column within table contain table useful rare cases
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Databases
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security safety features new windows vista number security safety features new windows vista available prior microsoft windows operating system release beginning early 2002 microsoft announcement trustworthy computing initiative great deal work gone making windows vista secure operating system predecessors internally microsoft adopted security development lifecycle underlying ethos secure design secure default secure deployment new code windows vista developed sdl methodology existing code reviewed refactored improve security specific areas windows vista introduces new security safety mechanisms include user account control parental controls network access protection built-in anti-malware tool new digital content protection mechanisms user account control new infrastructure requires user consent allowing action requires administrative privileges feature users including users administrative privileges run standard user mode default since applications require higher privileges action attempted needs administrative privileges installing new software changing system settings windows prompt user whether allow action user chooses allow process initiating action elevated higher privilege context continue standard users need enter username password administrative account get process elevated over-the-shoulder credentials administrator choose prompted consent ask credentials uac asks credentials secure desktop mode entire screen faded temporarily disabled present elevation ui prevent spoofing ui mouse application requesting elevation application requesting elevation focus switch secure desktop occurs taskbar icon blinks focussed elevation ui presented however possible prevent malicious application silently obtaining focus since secure desktop allows highest privilege system applications run user mode application present dialog boxes desktop prompt elevation consent safely assumed genuine additionally also help protect shatter attacks intercept windows inter-process messages run malicious code spoof user interface preventing unauthorized processes sending messages high privilege processes process wants send message high privilege process must get elevated higher privilege context via uac applications written assumption user running administrator privileges experienced problems earlier versions windows run limited user accounts often attempted write machine-wide system directories program files registry keys notably hklm uac attempts alleviate using file registry virtualization redirects writes subsequent reads per-user location within user ’ profile example application attempts write “ c \program files\appname\settings.ini ” user ’ permissions write directory write get redirected “ c \users\username\appdata\local\virtualstore\program files\appname\. ” bitlocker formerly known secure startup feature offers full disk encryption system volume using command-line utility possible encrypt additional volumes bitlocker utilizes usb key trusted platform module tpm version 1.2 tcg specifications store encryption key ensures computer running windows vista starts known-good state also protects data unauthorized access data volume encrypted full volume encryption key fvek encrypted volume master key vmk stored disk windows vista first microsoft windows operating system offer native support tpm 1.2 providing set apis commands classes services use management tpm new system service referred tpm base services enables access sharing tpm resources developers wish build applications support device encrypting file system efs windows vista used encrypt system page file per-user offline files cache efs also tightly integrated enterprise public key infrastructure pki supports using pki-based key recovery data recovery efs recovery certificates combination two also new group policies require smart cards efs enforce page file encryption stipulate minimum key lengths efs enforce encryption user ’ documents folder prohibit self-signed certificates efs encryption key cache cleared user locks workstation certain time limit efs rekeying wizard allows user choose certificate efs select migrate existing files use newly chosen certificate certificate manager also allows users export efs recovery certificates private keys users reminded back efs keys upon first use balloon notification rekeying wizard also used migrate users existing installations software certificates smart cards wizard also used administrator users recovery situations method efficient decrypting reencrypting files windows vista significantly improves firewall address number concerns around flexibility windows firewall corporate environment windows vista includes windows defender microsoft anti-spyware utility according microsoft renamed 'microsoft antispyware features scanning system spyware similar free products market also includes real time security agents monitor several common areas windows changes may caused spyware areas include internet explorer configuration downloads auto-start applications system configuration settings add-ons windows windows shell extensions windows defender also includes ability remove activex applications installed block startup programs also incorporates spynet network allows users communicate microsoft send consider spyware check applications acceptable windows vista allow administrators enforce hardware restrictions via group policy prevent users installing devices restrict device installation predefined white list restrict access removable media classes devices windows vista includes range parental controls non-domain user accounts parental controls allows administrators set restrictions monitor computer activity parental controls relies user account control much functionality features include features extensible replaced parental control applications using parental controls application programming interfaces apis windows vista uses address space layout randomization aslr load system files random addresses memory default system files loaded randomly possible 256 locations executables specifically set bit header portable executable pe file file format windows executables use aslr executables stack heap allocated randomly decided loading system files random addresses becomes harder malicious code know privileged system functions located thereby making unlikely predictably use helps prevent remote execution attacks preventing return-to-libc buffer overflow attacks portable executable format updated support embedding exception handler address header whenever exception thrown address handler verified one stored executable header match exception handled otherwise indicates run-time stack compromised hence process terminated function pointers obfuscated xor-ing random number actual address pointed hard retrieve would manually change pointer obfuscation key used pointer would hard retrieve thus made hard unauthorized user function pointer able actually use also metadata heap blocks xor-ed random numbers addition check-sums heap blocks maintained used detect unauthorized changes heap corruption whenever heap corruption detected application killed prevent successful completion exploit windows vista binaries include intrinsic support detection stack-overflow stack overflow windows vista binaries detected process killed used carry exploit also windows vista binaries place buffers higher memory non buffers like pointers supplied parameters lower memory area actually exploit buffer underrun needed gain access locations however buffer underruns much less common buffer overruns windows vista offers full support nx no-execute feature modern processors dep introduced windows xp service pack 2 windows server 2003 service pack 1 feature present nx evp amd amd64 processors xd edb intel processors flag certain parts memory containing data instead executable code prevents overflow errors resulting arbitrary code execution processor supports nx-bit windows vista automatically enforces hardware-based data execution prevention processes mark memory pages non-executable data segments like heap stack subsequently data prevented interpreted executed code prevents exploit code injected data executed dep enabled applications users gain additional resistance zero-day exploits applications dep-compliant generate dep exceptions therefore dep enforced applications default 32-bit versions windows turned critical system components however windows vista introduces additional nx policy controls allow software developers enable nx hardware protection code independent system-wide compatibility enforcement settings developers mark applications nx-compliant built allows protection enforced application installed runs enables higher percentage nx-protected code software ecosystem 32-bit platforms default system compatibility policy nx configured protect operating system components x86-64 applications backward compatibility issue therefore dep enforced default 64-bit programs also processor-enforced dep used x86-64 versions windows vista greater security new digital rights management content-protection features introduced windows vista help digital content providers corporations protect data copied inclusion new digital rights management features source criticism windows vista windows vista introduces mandatory integrity control set integrity levels processes low integrity process access resources higher integrity process feature used enforce application isolation applications medium integrity level applications running standard user context hook system level processes run high integrity level administrator mode applications hook onto lower integrity processes like windows internet explorer 7 8 lower privilege process perform window handle validation higher process privilege sendmessage postmessage higher privilege application windows use thread hooks attach higher privilege process use journal hooks monitor higher privilege process perform dll–injection higher privilege process windows service hardening compartmentalizes services one service compromised easily attack services system prevents windows services operations file systems registry networks supposed thereby reducing overall attack surface system preventing entry malware exploiting system services services assigned per-service security identifier sid allows controlling access service per access specified security identifier per-service sid may assigned service installation via changeserviceconfig2 api using sc.exe command sidtype verb services also use access control lists acl prevent external access resources private services windows vista also run less privileged account local service network service instead system account previous versions windows ran system services login session locally logged-in user session 0 windows vista session 0 reserved services interactive logins done sessions intended help mitigate class exploits windows message-passing system known shatter attacks process hosting service privileges specified requiredprivileges registry value hklm\system\currentcontrolset\services services also need explicit write permissions write resources per-service basis using write-restricted access token resources modified service given write access trying modify resource fails services also pre-configured firewall policy gives much privilege needed function properly independent software vendors also use windows service hardening harden services windows vista also hardens named pipes used rpc servers prevent processes able hijack graphical identification authentication gina used secure authentication interactive logon replaced credential providers combined supporting hardware credential providers extend operating system enable users log biometric devices fingerprint retinal voice recognition passwords pins smart card certificates custom authentication package schema third party developers wish create smart card authentication flexible certificate requirements relaxed enterprises may develop deploy optionally enforce custom authentication mechanisms domain users credential providers may designed support single sign-on sso authenticating users secure network access point leveraging radius technologies well machine logon credential providers also designed support application-specific credential gathering may used authentication network resources joining machines domain provide administrator consent user account control authentication also supported using ipv6 web services new security service provider credssp available security support provider interface enables application delegate user ’ credentials client using client-side ssp target server server-side ssp credssp also used terminal services provide single sign-on windows vista authenticate user accounts using smart cards combination passwords smart cards two-factor authentication windows vista also use smart cards store efs keys makes sure encrypted files accessible long smart card physically available smart cards used logon efs operates single sign-on mode uses logon smart card file encryption without prompting pin fast user switching limited workgroup computers windows xp also enabled computers joined domain starting windows vista windows vista also includes authentication support read-only domain controllers introduced windows server 2008 windows vista features update crypto api known cryptography api next generation cng cng api user mode kernel mode api includes support elliptic curve cryptography ecc number newer algorithms part national security agency nsa suite b extensible featuring support plugging custom cryptographic apis cng runtime also integrates smart card subsystem including base csp module implements standard backend cryptographic functions developers smart card manufacturers need write complex csps microsoft certificate authority issue ecc certificates certificate client enroll validate ecc sha-2 based certificates revocation improvements include native support online certificate status protocol ocsp providing real-time certificate validity checking crl prefetching capi2 diagnostics certificate enrollment wizard-based allows users input data enrollment provides clear information failed enrollments expired certificates certenroll new com-based enrollment api replaces xenroll library flexible programmability credential roaming capabilities replicate active directory key pairs certificates credentials stored stored user names passwords within network windows vista introduces network access protection nap ensures computers connecting communicating network conform required level system health set administrator network depending policy set administrator computers meet requirements either warned granted access allowed access limited network resources denied access completely nap also optionally provide software updates non-compliant computer upgrade level required access network using remediation server conforming client given health certificate uses access protected resources network network policy server running windows server 2008 acts health policy server clients need use windows xp sp3 later vpn server radius server dhcp server also act health policy server number specific security reliability changes made
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Operating systems
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citrus project citrus comprehensive i18n framework towards respectable unix systems project aims implement complete multilingual programming environment bsd-based operating systems goals include creation following things freebsd netbsd openbsd bsd/os dragonfly bsd aim reach level functionality solaris 7
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Operating systems
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class variable object-oriented programming classes class variable variable declared codice_1 modifier single copy exists regardless many instances class exist note java terms field variable used interchangeably class variable instance variable special type class attribute class property field data member dichotomy instance class members applies methods member functions well class may instance methods class methods languages class variables class methods either statically resolved via dynamic dispatch memory statically allocated compile time entire class static variables dynamically allocated run time every instantiation object cases however either dynamic example classes dynamically defined run time class variables classes allocated dynamically class defined languages class methods also dispatched dynamically thus languages static member variable static member function used synonymously place class variable class function synonymous across languages terms commonly used java c c++ class variables class methods declared codice_1 keyword referred static member variables static member functions c++ example class variable codice_3 incremented call constructor codice_3 always holds number requests constructed new request object given codice_5 sequential order since codice_6 class variable one object codice_3 contrast request object contains distinct codice_5 field also note variable codice_3 initialized
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Programming language topics
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iec 60870-6 iec 60870 part 6 one iec 60870 set standards define systems used telecontrol supervisory control data acquisition electrical engineering power system automation applications iec technical committee 57 working group 03 developed part 6 provide communication profile sending basic telecontrol messages two systems compatible iso standards itu-t recommendations standards include typical national power grid includes hierarchy control centres manage generation transmission distribution power throughout grid prior development electronics telecommunications networks co-ordination control centres carried telephone however development scada supervisory control data acquisition systems allowed remote control monitoring electrical plant centralised control centres initially individual scada manufacturers developed proprietary closed protocols communicating control centre electrical equipment field followed development open industry-standard protocols dnp3 iec 61850 however none communication protocols suited requirements communicating control centres meet special requirements communication co-ordination control centres iec developed iec 60870 set standards inter-control center communications protocol iccp iec 60870-6/tase.2 specified utility organizations throughout world provide data exchange wide area networks wans utility control centers utilities power pools regional control centers non-utility generators iccp also international standard international electrotechnical commission iec telecontrol application service element 2 tase.2 inter-utility real time data exchange become critical operation interconnected systems parts world example development electricity markets seen management electricity networks functional hierarchy split across boundaries commercial entities top level typically system operator coordination responsibilities dispatch overall system security regional transmission companies tie together distribution companies generating companies continental power systems considerable interconnection across international borders iccp allows exchange real time historical power system information including status control data measured values scheduling data energy accounting data operator messages historically reliance custom proprietary links protocols exchange real time data systems iccp began effort develop international standard real-time data exchange within electric power utility industry working group formed 1991 develop protocol standard develop prototype test specification submit specification iec standardisation carry interoperability testing developing vendors initial driver meet european common market requirements 1992 official designation first protocol tase.1 telecontrol application service element-1 second protocol tase.2 making use manufacturing message specification mms appears version become popular us iccp networks widely used tie together groups utility companies typically regional system operator transmission utilities distribution utilities generators regional operators may also connected together co-ordinate import export power regions across major inter-ties basic iccp functionality specified “ conformance blocks ” listed objects used convey data defined various parts iec 60870-6 block description data examples iccp based client server principles data transfers result request control centre client another control centre server control centres may clients servers iccp operates physical interfaces transport network services fit model supported tcp/ip ethernet 802.3 seems common iccp may operate single point-to-point link two control centres however general case many control centres routed wide area network logical connections “ associations ” control centres completely general client may establish associations one server client may establish one association server multiple associations server established different levels quality service high priority real time data delayed lower priority non real time data transfers iccp provide authentication encryption services normally provided lower protocol layers iccp uses “ bilateral tables ” control access bilateral table represents agreement two control centres connected iccp link agreement identifies data elements objects accessed via link level access permitted iccp link established contents bilateral tables server client provide complete control accessible party must matching entries server client tables provide access data objects wide acceptance iccp utility industry resulted several iccp products market although interoperability regarded high risk area standard implementation support conformance blocks order claim compliance standard minimal implementation requires block 1 blocks necessary achieve required functionality need implemented also necessary support objects defined standard particular block extensive interoperability testing products major vendors feature iccp protocol development independent reports available doubt reports vendors iccp purchaser must define functionality required terms conformance blocks required objects within blocks application profiles iccp client server conformances must match link operate successfully iccp real time data exchange protocol providing features data transfer monitoring control complete iccp link need facilities manage configure link monitor performance iccp standard specify interface requirements features necessary nevertheless affect interoperability similarly failover redundancy schemes way scada responds iccp requests protocol issue specified non protocol specific features referred standard “ local implementation issues ” iccp implementers free handle issues way wish local implementation means developers differentiate product market added value additional money spent product well-developed maintenance diagnostic tools may well saved many times life product use iccp connection expected grow change commercial iccp products generally available one three configurations embedded protocol iccp management tools interfaces part complete suite tools scada configuration offers maximum performance direct access scada database without requiring intervening buffering approach may available addition legacy system iccp application may restricted accessing scada environment embedded networked server making use industry standard communications networking scada host may provide performance approaching embedded iccp application application interface side iccp restricted scada environment open systems separate data historian databases security may easier manage iccp server segregated operational real time systems gateway processor approach similar networked server except intended legacy systems minimal communications networking capability lowest performance minimal situation iccp gateway may communicate scada host via serial port similar manner scada rtus
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Computer security
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digital scriptorium digital scriptorium ds non-profit tax-exempt consortium american libraries collections pre-modern manuscripts manuscripts made tradition books printing ds database represents manuscript collections web-based union catalog teaching scholarly research medieval renaissance studies provides access illuminated textual manuscripts online cataloging records supported high resolution digital images retrievable various topic searches ds database open access resource enables users study rare valuable materials academic research public libraries makes available collections often restricted public access includes famous masterpieces book illumination also understudied manuscripts previously overlooked publication study funded grants andrew w. mellon foundation national endowment humanities gladys krieble delmas foundation ds inception 1997 joint project bancroft library university california berkeley prof. charles faulhaber rare book manuscript library columbia university dr. consuelo w. dutschke plan digitize make available world wide web catalog records selected images two universities medieval early renaissance manuscript collections decision favor sample images rather complete imaging manuscripts originally practical today ds includes records sample complete imaging records sample images offer various pathways entrance growing corpus medieval renaissance manuscripts available online patterns collecting 19th early 20th century moreover many manuscripts american collections comprise partial texts detached single leaves cataloging many fragmentary works possible increases chance manuscripts could reconstituted virtually thus philosophical principle ds includes large small collections complete bound books single leaves 1999 2002 additional holdings huntington library university texas austin new york public library incorporated along number smaller collections database continued grow represents collections thirty member institutions including substantial repositories harvard university houghton library yale university beinecke library university pennsylvania also libraries rare works providence public library owns unusual 15th century bible wetmore ms 1 rebus format september 2015 ds counts catalog records 8,390 manuscripts 47,624 digitized images digital scriptorium database enables public viewing non-circulating materials normally available specialists restricted access visual catalog ds allows scholars verify cataloguing information places dates origin scripts artists quality special emphasis placed touchstone materials manuscripts signed dated scribes thus beginning american contribution goal established 1953 comité international de paléographie latine international committee latin paleography document photographically proportionately small number codices certain origin serve stylistically localize date vast quantities unsigned manuscripts ds publishes manuscripts firm attribution also ones need attention scholarship traditionally would unlikely candidates reproduction web-based also allows updates corrections matter form individual records ds acknowledge contributions outside scholars ds consortium consists academic public rare book libraries encourages broad audience benefits reciprocally beneficial body knowledge attending needs community specialists medievalists classicists musicologists paleographers diplomatists literary scholars art historians ds also recognizes public user community values rare unique works historical literary artistic significance working together ds consortium expanded resources libraries manage collections rare materials providing digital cataloging standard pre-modern manuscripts ds record includes extensive granular descriptive metadata supported high resolution digital images medieval renaissance manuscripts best served format-specific cataloging sensitive complexity hand-made books historical artifacts differ modern manuscripts letters personal records although unique objects usually unique texts may written bound decorated hand pre-modern manuscripts books text fourteenth-century missal example identified using early twentieth-century printed version text several collections may one manuscript st. augustine ’ de civitate dei city god ds search title fact retrieves fourteen copies work unique manuscripts dating 12th 15th centuries owned eight different libraries potential relationships among manuscripts means item-level bibliographic cataloging rather collection-based archival cataloging best identifies describes content medieval renaissance manuscripts works also historical artifactual significance catalog records medieval renaissance manuscripts need describe contents also complete provenance chain ownership binding may later period rest book marks ownership coats-of-arms physical condition material support usually parchment foliation construction book layout text attribution script date often estimated style localization decoration painted illustration names authors craftsmen scribes artists owners scholars medieval renaissance manuscripts less interested text manuscript aspect production field art history offers striking example scholar studying art illuminator mariano del buono care equally harvard manuscript copy plato manuscript held new york public library copy livy ds records factor interests allow searching physical features whether artist name example place date origin italy 1450-1499 would produce result digitization records medieval renaissance manuscripts excluded library public access catalogs instead published printed books written scholar-specialists similarly trained audience compared ds records similar library cataloging records simplified standardized concise specialists may notice ds record omits information collation available scholarly catalogs order avoid descriptions would take much time discourage library catalogers attempting task agreement green meisner goal product less process spanish proverb goes lo mejor es enemigo de lo bueno ds record thus intended serve ideal thorough description manuscript rather practical surrogate still provides better representation typical content-based opac online public access catalog record compared marc marc standards bibliographic standards used american libraries ds better designed describe content also historical context physical characteristics using sample images support descriptions sample images contain inherently descriptive information ds records include digital images although exceptions although ds records adapted marc formats ds better captures complexity medieval renaissance manuscripts marc example ds nests sections descriptive metadata order catalog manuscript multiple texts multiple origins one binding marc provides flat file deal coterminous text physical unit ds also indexes specific information pertinent format separate field artist example rather one personal names ds also creates focused records compared archival cataloging based ead encoded archival description latter collections-based designed descriptive searched item level thus ds cataloging method become unofficial library standard online cataloging medieval renaissance manuscripts united states university california berkeley provided first home ds database terms managing project devising initial technology interim period time 2003–2011 ds hosted columbia university returned original home berkeley technical innovations produced teams originating universities created digital product based progressive standards-based digitization policy originally using microsoft access serve cross-institutional data collection tool ds database used sgml later xml aggregate query combined information present platform managed u.c berkeley depends upon software known webgendb webgendb non-proprietary web-based interface underlying control database gendb gendb houses descriptive structural administrative metadata materials digitized web presentation outputs metadata using metadata encoding transmission standard mets format mets provides xml schema-based specification encoding hub documents materials whose content digital hub document draws together potentially dispersed related files data mets uses xml provide flexible vocabulary syntax identifying digital components together comprise digital object specifying location components expressing structural relationships digital components comprising digital object could include content files descriptive metadata administrative metadata mets used transfer dissemination and/or archiving digital objects compliance oais open archival information system reference model developed oclc ds reliance oais iso 14721 2003 promises secure digital preservation policy supported california digital library digital curation services cdl merritt digital archive
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Databases
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survivor 1987 video game survivor action game released 1987 spanish software house topo soft later re-released uk u.s. gold published several 8-bit formats including amstrad cpc msx zx spectrum player takes control alien bears striking resemblance race aliens alien series films aboard huge spacecraft filled many extraterrestrial creatures player must perpetuate alien race finding ten pods ship introducing incubators ship split 142 areas divided four zones zones joined doors air-vents player crawl zones also consist different levels connected lifts pods found large rooms different corridors vents make much spacecraft closely resemble sort room found 1980s platform games creatures ship dangerous player spit paralysing acid player limited amount energy sapped hostile creatures ship defence systems energy replenished managing place pod incubator eating one technicians found wandering around ship
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Computer architecture
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computer underground digest computer underground digest cud weekly online newsletter early internet cultural social legal issues published gordon meyer jim thomas march 1990 march 2000 meyer thomas criminal justice professors northern illinois university intended newsletter cover topical social legal issues generated rise telecommunications internet existed primarily email mailing list usenet though archives later provided website newsletter came prominence published legal commentary updates concerning hacker crackdowns federal indictments leonard rose craig neidorf phrack cud published commentary membership subjects including legal social implications growing internet later web book reviews topical publications many off-topic postings readership overtaken growth online forums web ceased publication march 2000
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Computer security
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internet security research group internet security research group isrg californian public-benefit corporation focuses internet security let encrypt—its first major initiative—aims make transport layer security tls certificates available free automated fashion josh aas serves group executive director board chair board also contains individuals akamai cisco university michigan mozilla aclu coreos electronic frontier foundation
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Computer security
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unix/32v unix/32v early version unix operating system bell laboratories released june 1979 32v direct port seventh edition unix dec vax architecture 32v unix primarily run dec pdp-11 computers bell labs group developed operating system dissatisfied dec members refused dec offer buy vax machine announced 1977 already begun unix port interdata 8/32 instead dec approached different bell labs group holmdel new jersey accepted offer started work become 32v performed tom london john f. reiser porting unix made possible due work done sixth seventh editions operating system decouple native pdp-11 environment 32v team first ported c compiler johnson pcc adapting assembler loader written interdata 8/32 version unix vax ported april 15 1978 version unix finding process bourne shell ... required far largest conversion effort supposedly portable program simple reason portable unix/32v released without paging virtual memory retaining swapping architecture seventh edition virtual memory system added berkeley bill joy özalp babaoğlu order support franz lisp released unix licensees third berkeley software distribution 3bsd 1979 thanks popularity two systems successors 4bsd unix system v unix/32v antecedent nearly modern unix systems
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Operating systems
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linux kernel mailing list linux kernel mailing list lkml main electronic mailing list linux kernel development majority announcements discussions debates flame wars kernel take place many mailing lists exist discuss different subsystems ports linux kernel lkml principal communication channel among linux kernel developers high-volume list usually receiving 1,000 messages day kernel code patches linux utilizes workflow governed lkml bazaar kernel development takes place book linux kernel development robert love notes lkml functions central place linux developers around world share patches argue implementation details discuss issues official releases linux kernel indicated email lkml new features discussed code posted list action taken also official place reporting bugs linux kernel case one find maintainer bug reported author michelle delio suggests lkml tux official linux mascot suggested refined although accuracy reporting stories disputed many companies associated linux kernel make announcements proposals lkml example novell intel vmware ibm etc list subscribers include linux kernel maintainers well known figures linux circles jeff v. merkey eric s. raymond etc. 2000 study found 14,535 people least 30 different countries sent least one email lkml 1995 2000 participate discussion linux development authors books linux kernel development model open source knowledge creation motivation software developers open source projects recovering device drivers made use lkml research studies surveys lwn.net website frequently cover discussion lkml newsletter kernel traffic covered activities linux-kernel mailing list november 2005 many internet websites include archives mailing list lore.kernel.org/lkml lkml.org mail-archive.com marc.info linus torvalds known angrily disagreeing developers lkml calling really unpleasant person later explained 'd like nice person curse less encourage people grow rather telling idiots 'm sorryi tried attitude torvalds considers necessary making point clear drawn opposition intel programmer sage sharp systemd developer lennart poettering among others 2018 torvalds took break kernel development work improving behavior instituted code conduct
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Computer architecture
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compaq presario 2700 presario 2700 series series laptop models released compaq computer corporation specific models series include presario 2700us 2701us 2710us presario 2700us released september 2001 featured intel pentium iii 256mb ram default upgradeable 1024mb 2700us also featured maximum screen resolution 1600 1200 pixels released january 2002 presario 2710us shipped 1.13ghz pentium 3 processor ati mobility radeon m6 graphics card 8mb video memory
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Computer architecture
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java platform module system java platform module system specifies distribution format collections java code associated resources also specifies repository storing collections modules identifies discovered loaded checked integrity includes features namespaces aim fixing shortcomings existing jar format especially jar hell lead issues classpath class loading problems java module system initially developed java community process jsr 277 scheduled released java 7 jsr 277 later put hold project jigsaw created modularize jdk jsr superseded jsr 376 java platform module system project jigsaw originally intended java 7 2011 deferred java 8 2014 part plan b deferred java 9 release 2017.. java 9 including java module system released september 21 2017 java module system implemented java 9 include following jeps jsr java specification request additionally several jdk 9 features added ease transition module system modules new way grouping code data contrary jar files modules explicitly declare modules depend packages export example following module declaration declares module com.foo.bar depends another com.foo.baz module exports following packages com.foo.bar.alpha com.foo.bar.beta contrary jar file format module describe dependencies module declaration placed file named module-info.java root module ’ source-file hierarchy jdk able check compile-time runtime jdk modularized java 9 java module system intend support functionalities osgi platform currently supports example life-cycle model services registry however java module system support functions supported osgi modularity compile-time built-in support native libraries couple articles exploring java module system osgi could interoperate published 2016 found infoq also osgi alliance blog
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Programming language topics
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xcore architecture xcore architecture 32-bit risc microprocessor architecture designed xmos architecture designed used multi-core processors embedded systems xcore executes eight concurrent threads thread register set architecture directly supports inter-thread inter-core communication various forms thread scheduling two versions xcore architecture exist xs1 architecture xs2 architecture processors xs1 architecture include xcore xs1-g4 xcore xs1-l1 processors xs2 architecture include xcore-200 architecture encodes instructions compactly using 16 bits frequently used instructions three operands 32 bits less frequently used instructions 6 operands almost instructions execute single cycle architecture event-driven order decouple timings program needs make execution speed program program normally perform computations wait event e.g message time external i/o event continuing two versions xcore architecture xs1 xs2 xs2 extending xs1 architecture xs1 architecture first xcore architecture defined 2007 implemented xcore xs1-g4 xcore xs1-l1 xcore xs1-su xcore xs1-ana former four-core processing node latter three single dual core processing nodes xs2 architecture defined 2015 implemented xcore-voice processors xcore-200 series processors latter marketed xl2 series general purpose xu2 series usb xe2 series rgmii versions embedded flash xs2 extends xs1 architecture limited form dual issue execution processor core comprises two lanes resource lane execute io operations general arithmetic memory lane execute memory operations branches general arithmetic short resource arithmetic instructions executed resource lane short memory branch arithmetic operations executed memory lane long instructions span lanes dual issue mode pairs instructions aligned 32-bit boundary instructions added aid high bandwidth processing dual-word load/store dual-word zip unzip bit byte strings dual word arithmetic saturation shift architecture comprises central execution unit operates set 25 registers surrounded number resources perform operations interact environment thread set hardware registers enabling threads execute concurrently instruction set comprises less standard sequential programming model instructions implement multi-threading multi-core i/o operations instructions access 12 general-purpose registers r0–r11 general completely interchangeable except instructions use r11 implicitly also 4 base registers usable instructions registers 16 24 accessible specialized instructions except first two r16 pc program counter r17 sr status register dedicated exception interrupt handling status register contains various mode bits processor standard alu result flags like carry zero negative overflow add subtract carry instructions exist specify five operand registers two inputs input carry one output output carry instructions 16-bit 32-bit encoding instructions use zero six operands common arithmetic operations add sub mult three-operand instructions based set 12 general purpose registers last four forms share opcode range number operands determined bits 5 10 last three forms use bit 4 additional opcode bit last form uses bits 1 0 well second form instructions loads stores use four bits encode register number allowing access r12–r15 instructions conditional branches allow register numbers 11 instead allowing third form share opcode range constants always unsigned many instructions come add/subtract pairs e.g jump forward backward form instruction determined four most-significant bits encoding three-operand register opcodes quite unusual since 12 registers power 2 encoding used fits zero three operands number operands 11 bits thus 5-bit opcode assigned four times three-operand instruction two-operand etc cases low 2 bits register number placed 2-bit field reducing problem encoding high bits range 0 2 three-operand form places low register numbers low 6 instruction bits high 2 bits register number combined base-3 number 0 26 using 9× +3× b c stored remaining 5 bits two-operand form uses unused 5 combinations 27–31 5-bit field operand used 2-bit field low bits reassigned one bit used additional opcode bit used additional combination register specifier doubling number available combinations 10 allowing 9 combinations 3× b c represented done manner similar bi-quinary coded decimal combination modulo 5 stored 5-bit field 3× b c mod 5 27 1-bit quotient ⌊ 3× b c /5⌋ stored instruction bit 5 marked asterisk table one-operand instructions use tenth combination value 6 bits set place register number 4 available bits operand c specified high bits stored b field finally one-operand encoding register number 12 b field contains binary 11 also used encode zero-operand instructions two low-order bits c field available additional opcode bits bringing total 8 instructions use register c field value 0–11 small immediate constant use select one 12 convenient bit-shift constants 0–8 16 24 32 less frequently used instructions encoded 32 bits 32-bit instructions allow 16- 20-bit immediate operands far branches six register operands example long multiply four source two destination operands additional opcode space rarely used instructions one 10-bit immediate opcode pfix opcode 111100 used add additional 10 bits 6- 10-bit immediate following instruction one three-operand opcode eopr opcode 11111 reserved additional operands prefix 3 operands used along following instruction word produce additional 32-bit instructions six operands also used rarely used three- two-operand instructions cases eopr specifies three two operands following instruction word zero-operand instruction two-operand case extra opcode bit leading eopr used thread access 12 general purpose registers r0 ... r11 addition 4 special purpose registers sp lr link register stores return address cp constant pool points part memory stores constants dp data pool points global variables addition 16 another 9 registers store pc kernel pc exception type exception data saved copies case exception interrupt instruction set load-store instruction set almost instructions execute single cycle instruction need data memory example arithmetic operations instruction prefetch word instructions instructions encoded 16-bits instructions loads stores typical number 20 loads stores 80 instructions prefetch mechanism stay ahead instructions stream acts like small instruction cache behaviour predicted compile time making timing behaviour predictable functional behaviour instructions access memory use base register sp dp cp pc general purpose register single 16-bit instruction thread access larger sections memory accessed means extended instructions extend ranges 64 kbytes scheme designed order densely encode common cases found many programming patterns access small stack frames small set globals constants structures arrays access bit fields odd length facilitated means sign zero extend instructions common arithmetic instructions provided including divide remainder instructions single cycle comparison instructions compute truth value 0 1 register avoiding use flags many instructions immediate version allows single operand value 0 11 inclusive encoding many common cases 1 case bit operations shift immediate value encodes common cases extra instructions provided reversing bits bytes count leading zeros digital signal processing long integer arithmetic branch instructions include conditional unconditional relative branches branch using address register provided relative branch adds scaled register operand program counter provided support jump tables branches instructions distance encoded single word procedure calling instructions include relative calls calls via constant pool indexed calls via dedicated register calls via register calls within single program module encoded single instruction inter-module calling requires two instructions callee save link-register leaf-function single instruction extends stack saves link register dual issue mode available xs2 enables one short load store branch instruction paired one short resource instruction short arithmetic instructions paired instruction enables inner-loops example transfer data memory io halved length issuing load instruction together add instruction change counter together branch instruction xs1 instruction set designed support multi threading multi-core computations extent supports channel communication support distributed memory computations barriers locks support shared memory computations thread initiates execution one newly allocated threads setting initial register values communication threads performed using channels provide full-duplex data transfer channel-ends enables amongst others implementation csp based languages languages based pi calculus instruction set agnostic channel connected whether inside core outside core channels carry messages constructed data control tokens two channel ends control tokens used encode communication protocols channel ends buffer able hold sufficient tokens allow least one word buffered output instruction executed channel full take data thread executed instruction paused restarted enough room channel instruction successfully complete likewise input instruction executed enough data available thread paused restarted enough data becomes available thread single instruction synchronise group threads using barrier synchronisation alternatively thread synchronise using lock providing mutual exclusion order communicate data using barriers locks threads either write data registers another thread access memory another thread provided threads execute core shared memory used compiler programmer must ensure race conditions xs2 architecture 'priority mode enables threads run high priority low priority threads guaranteed progress high priority threads guaranteed thread cycle ready execute xs1 architecture event-driven instruction dispatch external events addition traditional interrupts program chooses use events underlying processor expect event wait specific place handled synchronously desired i/o handled asynchronously using interrupts events interrupts used resource implementation supports common resources supported ports external input output timers allow timing reference clock channels allow communication synchronization threads within core threads different cores locks allow controlled access shared memory synchronizers implement barrier synchronizations threads
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Computer architecture
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meta-scheduling meta-scheduling super scheduling computer software technique optimizing computational workloads combining organization multiple distributed resource managers single aggregated view allowing batch jobs directed best location execution meta-scheduling technique solution scheduling set depended independent faults different scenarios mapping modeling event-tree used dynamic static scheduling method work use static scheduling adaptive tt mpsoc systems meta-scheduling described technique optimize computational workload combining organizing multiple distributed resources integrated view words extended data-flow model quasi-static scheduling dynamic behaviour changes scenario-based multi-mode approaches essential techniques embedded-systems e.g. design space exploration mpsocs reconfigurable systems optimization techniques generation schedule graphs supporting sbmes approach developed implemented sbmes promise better performance reducing dynamic scheduling overhead recovering faults following partial list noteworthy open source commercial meta-schedulers currently available
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Distributed computing architecture
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computer worm computer worm standalone malware computer program replicates order spread computers often uses computer network spread relying security failures target computer access worms almost always cause least harm network even consuming bandwidth whereas viruses almost always corrupt modify files targeted computer many worms designed spread attempt change systems pass however morris worm mydoom showed even payload-free worms cause major disruption increasing network traffic unintended effects actual term worm first used john brunner 1975 novel shockwave rider novel nichlas haflinger designs sets data-gathering worm act revenge powerful men run national electronic information web induces mass conformity biggest-ever worm loose net automatically sabotages attempt monitor ... never worm tough head long tail november 2 1988 robert tappan morris cornell university computer science graduate student unleashed became known morris worm disrupting large number computers internet guessed time one tenth connected morris appeal process u.s. court appeals estimated cost removing virus installation 200 53,000 work prompted formation cert coordination center phage mailing list morris became first person tried convicted 1986 computer fraud abuse act code designed spread worm typically referred payload typical malicious payloads might delete files host system e.g. explorezip worm encrypt files ransomware attack exfiltrate data confidential documents passwords probably common payload worms install backdoor allows computer remotely controlled worm author zombie networks machines often referred botnets commonly used range malicious purposes including sending spam performing dos attacks worms spread exploiting vulnerabilities operating systems vendors security problems supply regular security updates see patch tuesday installed machine majority worms unable spread vulnerability disclosed security patch released vendor zero-day attack possible users need wary opening unexpected email run attached files programs visit web sites linked emails however iloveyou worm increased growth efficiency phishing attacks remains possible trick end-user running malicious code anti-virus anti-spyware software helpful must kept up-to-date new pattern files least every days use firewall also recommended april–june 2008 issue ieee transactions dependable secure computing computer scientists described new potentially effective way combat internet worms researchers discovered contain worms scanned internet randomly looking vulnerable hosts infect found key use software monitor number scans machines network send machine started send many scans sign infected allowed administrators take line check malware addition machine learning techniques used detect new worms analyzing behavior suspected computer users minimize threat posed worms keeping computers operating system software date avoiding opening unrecognized unexpected emails running firewall antivirus software mitigation techniques include beginning first research worms xerox parc attempts create useful worms worms allowed testing john shoch jon hupp ethernet principles network xerox alto computers nachi family worms tried download install patches microsoft website fix vulnerabilities host system—by exploiting vulnerabilities practice although may made systems secure generated considerable network traffic rebooted machine course patching work without consent computer owner user regardless payload writers intentions security experts regard worms malware several worms like xss worms written research worms spread example effects changes social activity user behavior one study proposed seems first computer worm operates second layer osi model data link layer utilizes topology information content-addressable memory cam tables spanning tree information stored switches propagate probe vulnerable nodes enterprise network covered
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Computer security
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processor control region processor control region pcr windows kernel mode data structure contains information current processor accessed via fs segment register x86 versions gs segment register x64 versions respectively windows pcr known kpcr contains information current processor pcr contains substructure called processor control block kprcb contains information cpu step pointer thread object current thread
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Computer architecture
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systembuilder/sb+ systembuilder 4gl development runtime environment originally written pick family computer databases/environments part rocket u2 software suite systembuilder environment comprises sb+ server often running rocket u2 database sbclient runs microsoft windows desktop application product run either developer runtime mode development environment enables rapid prototyping development deployment applications includes rudimentary gui application environment system builder started garden shed south africa first cousins neill derek miller 1982 popularity pick database system combined lack good development framework led develop tool build standard menus screens system builder software company incorporated isle man cousins moved sydney australia early 1980s product successful expanding international markets versions began re-develop product ground become sb+ released early 1990 traditionally time pick systems accessed using dumb green-screen terminals rise pc new paradigm presented around end 1991 product enhanced addition specialised terminal emulation client called termulator able tightly integrate server pc allow facilities like downloads direct server lotus 1-2-3 new kid block microsoft excel shortly client program renamed sbclient ability render server 'green-screens client gui screens added clever set driver interpreters bought unidata corporation 1996 following unidata merger vmark software form ardent software 1998 systembuilder product set came ownership informix 2000 following purchase ardent software datastage product subsequently 2001 informix bought ibm u2 systembuilder products eventually found way become part ibm data management portfolio development systembuilder redback products continued sydney 2005 merged u2 development team located denver united states recently 1 october 2009 rocket software announced purchase entire u2 suite includes systembuilder ibm system builder/sb+ server environment based around set key tools utilities leverage provide powerful comprehensive development environment built mainly tools sb+ includes application menuing system screen generator 3gl programming language expression language gui components report writer tool recent iteration system builder sb/xa v6.5.2 released oct 2017 sb/xa includes many major enhancements including new gui system based xaml
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Programming language topics
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dnotify dnotify file system event monitor linux kernel one subfeatures fcntl call introduced 2.4 kernel series obsoleted inotify retained compatibility reasons function essentially extension filesystems notice changes filesystem report changes applications instead application checking changes filesystem application register notified kernel changes filesystem occur application select directories monitor types changes notified one major use desktop search utilities like beagle functionality permits reindexing changed files without scanning filesystem changes every minutes would inefficient told file changed directly kernel rather actively looking beagle utilities achieve change-to-reindexing times second small performance hits dnotify therefore enables use programs sensible manner daemons generally accepted distributors drain system performance noticeably provide userland functionality
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Operating systems
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c programming language c letter c general-purpose procedural computer programming language supporting structured programming lexical variable scope recursion static type system prevents unintended operations design c provides constructs map efficiently typical machine instructions found lasting use applications previously coded assembly language applications include operating systems well various application software computers ranging supercomputers embedded systems c originally developed bell labs dennis ritchie 1972 1973 make utilities running unix later applied re-implementing kernel unix operating system 1980s c gradually gained popularity nowadays one widely used programming languages c compilers various vendors available majority existing computer architectures operating systems c standardized ansi since 1989 see ansi c subsequently international organization standardization c imperative procedural language designed compiled using relatively straightforward compiler provide low-level access memory provide language constructs map efficiently machine instructions require minimal runtime support despite low-level capabilities language designed encourage cross-platform programming standards-compliant c program written portability mind compiled wide variety computer platforms operating systems changes source code language become available various platforms embedded microcontrollers supercomputers like procedural languages algol tradition c facilities structured programming allows lexical variable scope recursion static type system prevents unintended operations c executable code contained within subroutines also called functions though strictly sense functional programming function parameters always passed value pass-by-reference simulated c explicitly passing pointer values c program source text free-format using semicolon statement terminator curly braces grouping blocks statements c language also exhibits following characteristics c include certain features found languages object orientation garbage collection implemented emulated often use external libraries e.g. glib object system boehm garbage collector many later languages borrowed directly indirectly c including c++ c unix c shell go java javascript limbo lpc objective-c perl php python rust swift verilog systemverilog hardware description languages languages drawn many control structures basic features c. python dramatic exception also express highly similar syntax c tend combine recognizable expression statement syntax c underlying type systems data models semantics radically different origin c closely tied development unix operating system originally implemented assembly language pdp-7 dennis ritchie ken thompson incorporating several ideas colleagues eventually decided port operating system pdp-11 original pdp-11 version unix developed assembly language thompson needed programming language make utilities first tried make fortran compiler soon gave idea made new language b thompson simplified version bcpl however utilities written b b slow b could take advantage pdp-11 features byte addressability 1972 ritchie started improve b resulted creating new language c. c compiler utilities made included version 2 unix version 4 unix released nov. 1973 unix kernel extensively re-implemented c. time c language acquired powerful features codice_12 types unix one first operating system kernels implemented language assembly earlier instances include multics system written pl/i master control program mcp burroughs b5000 written algol 1961 around 1977 ritchie stephen c. johnson made changes language facilitate portability unix operating system johnson portable c compiler served basis several implementations c new platforms 1978 brian kernighan dennis ritchie published first edition c programming language book known c programmers k r served many years informal specification language version c describes commonly referred k r c second edition book covers later ansi c standard described k r introduced several language features even publication 1989 ansi standard many years k r c still considered lowest common denominator c programmers restricted maximum portability desired since many older compilers still use carefully written k r c code legal standard c well early versions c functions return types codice_30 must declared used function definition functions used without prior declaration presumed return type codice_30 example codice_30 type specifiers commented could omitted k r c required later standards since k r function declarations include information function arguments function parameter type checks performed although compilers would issue warning message local function called wrong number arguments multiple calls external function used different numbers types arguments separate tools unix lint utility developed among things could check consistency function use across multiple source files years following publication k r c several features added language supported compilers particular pcc vendors included large number extensions lack agreement standard library together language popularity fact even unix compilers precisely implemented k r specification led necessity standardization late 1970s 1980s versions c implemented wide variety mainframe computers minicomputers microcomputers including ibm pc popularity began increase significantly 1983 american national standards institute ansi formed committee x3j11 establish standard specification c. x3j11 based c standard unix implementation however non-portable portion unix c library handed ieee working group 1003 become basis 1988 posix standard 1989 c standard ratified ansi x3.159-1989 programming language c version language often referred ansi c standard c sometimes c89 1990 ansi c standard formatting changes adopted international organization standardization iso iso/iec 9899:1990 sometimes called c90 therefore terms c89 c90 refer programming language ansi like national standards bodies longer develops c standard independently defers international c standard maintained working group iso/iec jtc1/sc22/wg14 national adoption update international standard typically occurs within year iso publication one aims c standardization process produce superset k r c incorporating many subsequently introduced unofficial features standards committee also included several additional features function prototypes borrowed c++ codice_15 pointers support international character sets locales preprocessor enhancements although syntax parameter declarations augmented include style used c++ k r interface continued permitted compatibility existing source code c89 supported current c compilers c code written today based program written standard c without hardware-dependent assumptions run correctly platform conforming c implementation within resource limits without precautions programs may compile certain platform particular compiler due example use non-standard libraries gui libraries reliance compiler- platform-specific attributes exact size data types byte endianness cases code must compilable either standard-conforming k r c-based compilers codice_38 macro used split code standard k r sections prevent use k r c-based compiler features available standard c. ansi/iso standardization process c language specification remained relatively static several years 1995 normative amendment 1 1990 c standard iso/iec 9899/amd1:1995 known informally c95 published correct details add extensive support international character sets c standard revised late 1990s leading publication iso/iec 9899:1999 1999 commonly referred c99 since amended three times technical corrigenda c99 introduced several new features including inline functions several new data types including codice_39 codice_40 type represent complex numbers variable-length arrays flexible array members improved support ieee 754 floating point support variadic macros macros variable arity support one-line comments beginning codice_41 bcpl c++ many already implemented extensions several c compilers c99 part backward compatible c90 stricter ways particular declaration lacks type specifier longer codice_30 implicitly assumed standard macro codice_43 defined value codice_44 indicate c99 support available gcc solaris studio c compilers support many new features c99 c compiler microsoft visual c++ however implements c89 standard parts c99 required compatibility c++11 2007 work began another revision c standard informally called c1x official publication 2011-12-08 c standards committee adopted guidelines limit adoption new features tested existing implementations c11 standard adds numerous new features c library including type generic macros anonymous structures improved unicode support atomic operations multi-threading bounds-checked functions also makes portions existing c99 library optional improves compatibility c++ standard macro codice_43 defined codice_46 indicate c11 support available published june 2018 c18 current standard c programming language introduces new language features technical corrections clarifications defects c11 standard macro codice_43 defined codice_48 historically embedded c programming requires nonstandard extensions c language order support exotic features fixed-point arithmetic multiple distinct memory banks basic i/o operations 2008 c standards committee published technical report extending c language address issues providing common standard implementations adhere includes number features available normal c fixed-point arithmetic named address spaces basic i/o hardware addressing c formal grammar specified c standard line endings generally significant c however line boundaries significance preprocessing phase comments may appear either delimiters codice_49 codice_50 since c99 following codice_41 end line comments delimited codice_49 codice_50 nest sequences characters interpreted comment delimiters appear inside string character literals c source files contain declarations function definitions function definitions turn contain declarations statements declarations either define new types using keywords codice_12 codice_35 codice_14 assign types perhaps reserve storage new variables usually writing type followed variable name keywords codice_57 codice_30 specify built-in types sections code enclosed braces codice_59 codice_60 sometimes called curly brackets limit scope declarations act single statement control structures imperative language c uses statements specify actions common statement expression statement consisting expression evaluated followed semicolon side effect evaluation functions may called variables may assigned new values modify normal sequential execution statements c provides several control-flow statements identified reserved keywords structured programming supported codice_61 -codice_62 conditional execution codice_63-codice_4 codice_4 codice_2 iterative execution looping codice_2 statement separate initialization testing reinitialization expressions omitted codice_68 codice_69 used leave innermost enclosing loop statement skip reinitialization also non-structured codice_70 statement branches directly designated label within function codice_5 selects codice_72 executed based value integer expression expressions use variety built-in operators may contain function calls order arguments functions operands operators evaluated unspecified evaluations may even interleaved however side effects including storage variables occur next sequence point sequence points include end expression statement entry return function call sequence points also occur evaluation expressions containing certain operators codice_73 codice_10 codice_75 comma operator permits high degree object code optimization compiler requires c programmers take care obtain reliable results needed programming languages kernighan ritchie say introduction c programming language c like language blemishes operators wrong precedence parts syntax could better c standard attempt correct many blemishes impact changes already existing software basic c source character set includes following characters newline indicates end text line need correspond actual single character although convenience c treats one additional multi-byte encoded characters may used string literals entirely portable latest c standard c11 allows multi-national unicode characters embedded portably within c source text using codice_83 codice_84 encoding codice_85 denotes hexadecimal character although feature yet widely implemented basic c execution character set contains characters along representations alert backspace carriage return run-time support extended character sets increased revision c standard c89 32 reserved words also known keywords words used purposes predefined c99 reserved five words c11 reserved seven words recently reserved words begin underscore followed capital letter identifiers form previously reserved c standard use implementations since existing program source code using identifiers would affected c implementations started supporting extensions programming language standard headers define convenient synonyms underscored identifiers language previously included reserved word called codice_130 seldom implemented removed reserved word c supports rich set operators symbols used within expression specify manipulations performed evaluating expression c operators c uses operator codice_136 used mathematics express equality indicate assignment following precedent fortran pl/i unlike algol derivatives c uses operator codice_156 test equality similarity two operators assignment equality may result accidental use one place many cases mistake produce error message although compilers produce warnings example conditional expression codice_176 might mistakenly written codice_177 evaluated true codice_76 zero assignment c operator precedence always intuitive example operator codice_156 binds tightly executed prior operators codice_9 bitwise codice_149 bitwise expressions codice_182 must written codice_183 coder intent hello world example appeared first edition k r become model introductory program programming textbooks regardless programming language program prints hello world standard output usually terminal screen display original version main standard-conforming hello world program int main void first line program contains preprocessing directive indicated codice_184 causes compiler replace line entire text codice_185 standard header contains declarations standard input output functions codice_186 codice_187 angle brackets surrounding codice_185 indicate codice_185 located using search strategy prefers headers provided compiler headers name opposed double quotes typically include local project-specific header files next line indicates function named codice_190 defined codice_190 function serves special purpose c programs run-time environment calls codice_190 function begin program execution type specifier codice_30 indicates value returned invoker case run-time environment result evaluating codice_190 function integer keyword codice_15 parameter list indicates function takes arguments opening curly brace indicates beginning definition codice_190 function next line calls diverts execution function named codice_186 case supplied system library call codice_186 function passed provided single argument address first character string literal codice_199 string literal unnamed array elements type codice_57 set automatically compiler final 0-valued character mark end array codice_186 needs know codice_202 escape sequence c translates newline character output signifies end current line return value codice_186 function type codice_30 silently discarded since used careful program might test return value determine whether codice_186 function succeeded semicolon codice_206 terminates statement closing curly brace indicates end code codice_190 function according c99 specification newer codice_190 function unlike function implicitly return value codice_80 upon reaching codice_60 terminates function formerly explicit codice_211 statement required interpreted run-time system exit code indicating successful execution type system c static weakly typed makes similar type system algol descendants pascal built-in types integers various sizes signed unsigned floating-point numbers enumerated types codice_14 integer type codice_57 often used single-byte characters c99 added boolean datatype also derived types including arrays pointers records codice_12 unions codice_35 c often used low-level systems programming escapes type system may necessary compiler attempts ensure type correctness expressions programmer override checks various ways either using type cast explicitly convert value one type another using pointers unions reinterpret underlying bits data object way find c declaration syntax unintuitive particularly function pointers ritchie idea declare identifiers contexts resembling use declaration reflects use c usual arithmetic conversions allow efficient code generated sometimes produce unexpected results example comparison signed unsigned integers equal width requires conversion signed value unsigned generate unexpected results signed value negative c supports use pointers type reference records address location object function memory pointers dereferenced access data stored address pointed invoke pointed-to function pointers manipulated using assignment pointer arithmetic run-time representation pointer value typically raw memory address perhaps augmented offset-within-word field since pointer type includes type thing pointed expressions including pointers type-checked compile time pointer arithmetic automatically scaled size pointed-to data type pointers used many purposes c. text strings commonly manipulated using pointers arrays characters dynamic memory allocation performed using pointers many data types trees commonly implemented dynamically allocated codice_12 objects linked together using pointers pointers functions useful passing functions arguments higher-order functions qsort bsearch callbacks invoked event handlers null pointer value explicitly points valid location dereferencing null pointer value undefined often resulting segmentation fault null pointer values useful indicating special cases next pointer final node linked list error indication functions returning pointers appropriate contexts source code assigning pointer variable null pointer constant written codice_80 without explicit casting pointer type codice_218 macro defined several standard headers conditional contexts null pointer values evaluate false pointer values evaluate true void pointers codice_219 point objects unspecified type therefore used generic data pointers since size type pointed-to object known void pointers dereferenced pointer arithmetic allowed although easily many contexts implicitly converted object pointer type careless use pointers potentially dangerous typically unchecked pointer variable made point arbitrary location cause undesirable effects although properly used pointers point safe places made point unsafe places using invalid pointer arithmetic objects point may continue used deallocation dangling pointers may used without initialized wild pointers may directly assigned unsafe value using cast union another corrupt pointer general c permissive allowing manipulation conversion pointer types although compilers typically provide options various levels checking programming languages address problems using restrictive reference types array types c traditionally fixed static size specified compile time recent c99 standard also allows form variable-length arrays however also possible allocate block memory arbitrary size run-time using standard library codice_220 function treat array c unification arrays pointers means declared arrays dynamically allocated simulated arrays virtually interchangeable since arrays always accessed effect via pointers array accesses typically checked underlying array size although compilers may provide bounds checking option array bounds violations therefore possible rather common carelessly written code lead various repercussions including illegal memory accesses corruption data buffer overruns run-time exceptions bounds checking desired must done manually c special provision declaring multi-dimensional arrays rather relies recursion within type system declare arrays arrays effectively accomplishes thing index values resulting multi-dimensional array thought increasing row-major order multi-dimensional arrays commonly used numerical algorithms mainly applied linear algebra store matrices structure c array well suited particular task however since arrays passed merely pointers bounds array must known fixed values else explicitly passed subroutine requires dynamically sized arrays arrays accessed using double indexing workaround allocate array additional row vector pointers columns c99 introduced variable-length arrays address issues ordinary c arrays subscript notation codice_221 codice_222 designates pointer syntactic sugar codice_223 taking advantage compiler knowledge pointer type address codice_224 points base address pointed codice_222 incremented codice_27 bytes rather defined base address incremented codice_27 multiplied size element codice_222 points thus codice_221 designates codice_230th element array furthermore expression contexts notable exception operand codice_108 name array automatically converted pointer array first element implies array never copied whole named argument function rather address first element passed therefore although function calls c use pass-by-value semantics arrays effect passed reference size element determined applying operator codice_108 dereferenced element codice_222 codice_234 codice_235 number elements declared array codice_78 determined codice_237 latter applies array names variables declared subscripts codice_238 due semantics c possible determine entire size arrays pointers arrays created dynamic allocation codice_220 code codice_240 codice_241 designates pointer work since compiler assumes size pointer requested since array name arguments codice_108 converted pointers exhibit ambiguity however arrays created dynamic allocation accessed pointers rather true array variables suffer codice_108 issues array pointers thus despite apparent equivalence array pointer variables still distinction made even though name array expression contexts converted pointer first element pointer occupy storage array name l-value address constant unlike pointer variable consequently array points changed impossible assign new address array name array contents may copied however using codice_244 function accessing individual elements one important functions programming language provide facilities managing memory objects stored memory c provides three distinct ways allocate memory objects three approaches appropriate different situations various trade-offs example static memory allocation little allocation overhead automatic allocation may involve slightly overhead dynamic memory allocation potentially great deal overhead allocation deallocation persistent nature static objects useful maintaining state information across function calls automatic allocation easy use stack space typically much limited transient either static memory heap space dynamic memory allocation allows convenient allocation objects whose size known run-time c programs make extensive use three possible automatic static allocation usually simplest storage managed compiler freeing programmer potentially error-prone chore manually allocating releasing storage however many data structures change size runtime since static allocations automatic allocations c99 must fixed size compile-time many situations dynamic allocation necessary prior c99 standard variable-sized arrays common example see article codice_220 example dynamically allocated arrays unlike automatic allocation fail run time uncontrolled consequences dynamic allocation functions return indication form null pointer value required storage allocated static allocation large usually detected linker loader program even begin execution unless otherwise specified static objects contain zero null pointer values upon program startup automatically dynamically allocated objects initialized initial value explicitly specified otherwise initially indeterminate values typically whatever bit pattern happens present storage might even represent valid value type program attempts access uninitialized value results undefined many modern compilers try detect warn problem false positives false negatives occur another issue heap memory allocation synchronized actual usage program order reused much possible example pointer heap memory allocation goes scope value overwritten codice_249 called memory recovered later reuse essentially lost program phenomenon known memory leak conversely possible memory freed continue referenced leading unpredictable results typically symptoms appear portion program far removed actual error making difficult track problem issues ameliorated languages automatic garbage collection c programming language uses libraries primary method extension c library set functions contained within single archive file library typically header file contains prototypes functions contained within library may used program declarations special data types macro symbols used functions order program use library must include library header file library must linked program many cases requires compiler flags e.g. codice_250 shorthand link math library common c library c standard library specified iso ansi c standards comes every c implementation implementations target limited environments embedded systems may provide subset standard library library supports stream input output memory allocation mathematics character strings time values several separate standard headers example codice_185 specify interfaces standard library facilities another common set c library functions used applications specifically targeted unix unix-like systems especially functions provide interface kernel functions detailed various standards posix single unix specification since many programs written c wide variety libraries available libraries often written c c compilers generate efficient object code programmers create interfaces library routines used higher-level languages like java perl python file input output i/o part c language instead handled libraries c standard library associated header files e.g codice_185 file handling generally implemented high-level i/o works streams stream perspective data flow independent devices file concrete device high level i/o done association stream file c standard library buffer memory area queue temporarily used store data sent final destination reduces time spent waiting slower devices example hard drive solid state drive low-level i/o functions part standard c library generally part bare metal programming programming independent operating system embedded programming exceptions implementations include low-level i/o number tools developed help c programmers find fix statements undefined behavior possibly erroneous expressions greater rigor provided compiler tool lint first leading many others automated source code checking auditing beneficial language c many tools exist lint common practice use lint detect questionable code program first written program passes lint compiled using c compiler also many compilers optionally warn syntactically valid constructs likely actually errors misra c proprietary set guidelines avoid questionable code developed embedded systems also compilers libraries operating system level mechanisms performing actions standard part c bounds checking arrays detection buffer overflow serialization dynamic memory tracking automatic garbage collection tools purify valgrind linking libraries containing special versions memory allocation functions help uncover runtime errors memory usage c widely used systems programming implementing operating systems embedded system applications c code written portability used purposes yet needed system-specific code used access specific hardware addresses perform type punning match externally imposed interface requirements low run-time demand system resources c also used website programming using cgi gateway information web application server browser c often chosen interpreted languages speed stability near-universal availability one consequence c wide availability efficiency compilers libraries interpreters programming languages often implemented c. reference implementations python perl php example written c. layer abstraction thin overhead low c enables programmers create efficient implementations algorithms data structures useful computationally intense programs example gnu multiple precision arithmetic library gnu scientific library mathematica matlab completely partially written c. c sometimes used intermediate language implementations languages approach may used portability convenience using c intermediate language additional machine-specific code generators necessary c features line-number preprocessor directives optional superfluous commas end initializer lists support compilation generated code however c shortcomings prompted development c-based languages specifically designed use intermediate languages c -- c also widely used implement end-user applications however applications also written newer higher-level languages c directly indirectly influenced many later languages c go java javascript limbo lpc perl php python unix c shell pervasive influence syntactical languages mentioned combine statement less recognizably expression syntax c type systems data models and/or large-scale program structures differ c sometimes radically several c near-c interpreters exist including ch cint also used scripting object-oriented languages became popular c++ objective-c two different extensions c provided object-oriented capabilities languages originally implemented source-to-source compilers source code translated c compiled c compiler c++ programming language devised bjarne stroustrup approach providing object-oriented functionality c-like syntax c++ adds greater typing strength scoping tools useful object-oriented programming permits generic programming via templates nearly superset c c++ supports c exceptions objective-c originally thin layer top c remains strict superset c permits object-oriented programming using hybrid dynamic/static typing paradigm objective-c derives syntax c smalltalk syntax involves preprocessing expressions function declarations function calls inherited c syntax object-oriented features originally taken smalltalk addition c++ objective-c ch cilk unified parallel c nearly supersets c
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Programming language topics
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office online office online known 2014 office web apps july 2019 office online office suite offered microsoft allows users create edit files using lightweight microsoft office web apps word excel powerpoint onenote offering also includes outlook.com people calendar onedrive accessible unified app switcher users install on-premises version service called office online server private clouds conjunction sharepoint microsoft exchange server microsoft lync server office web apps first revealed october 2008 pdc 2008 los angeles chris capossela senior vice president microsoft business division introduced office web apps lightweight versions word excel powerpoint onenote allow people create edit collaborate office documents web browser according capossela office web apps become available part office live workspace office web apps announced powered ajax well silverlight however latter optional availability enhance user experience resulting sharper images improved rendering microsoft business division president stephen elop stated pdc 2008 technology preview office web apps would become available later 2008 however technical preview office web apps released 2009 july 13 2009 microsoft announced worldwide partners conference 2009 new orleans microsoft office 2010 reached technical preview development milestone features office web apps demonstrated public first time additionally microsoft announced office web apps would made available consumers online free charge microsoft software assurance customers option running premises office 2010 beta testers given access office web apps date announced would available testers august 2009 however august 2009 microsoft spokesperson stated delay release office web apps technical preview would available end august microsoft officially released technical preview office web apps september 17 2009 office web apps made available selected testers via onedrive time skydrive service final version office web apps made available public via windows live office june 7 2010 october 22 2012 microsoft announced release new features including co-authoring performance improvements touch support november 6 2013 microsoft announced new features including real-time co-authoring auto-save feature word replacing save button february 2014 office web apps re-branded office online incorporated microsoft web services including calendar onedrive outlook.com people microsoft previously attempted unify online services suite including microsoft passport hotmail msn messenger later skydrive brand known windows live first launched 2005 however impending launch windows 8 increased use cloud services microsoft dropped windows live brand emphasize services would built directly windows merely bolted add-on critics criticized windows live brand clear vision applied increasingly broad array unrelated services time windows live hotmail re-launched outlook.com sharing name microsoft outlook personal information manager july 2019 microsoft announced retiring online branding office online product office may referred office web office browser office online open edit documents spreadsheets presentations office open xml formats web starting july 2013 render pdf documents convert microsoft word documents although formatting document may deviate original since november 2013 apps supported real-time co-authoring autosave word files word online lacks two ribbons exist word 2013 references mailings mailing allows users print envelopes labels manage mail merge printing word documents references contains features needed advanced documents e.g table contents citations bibliography captions index table authorities word online change insert section breaks views available word desktop app outline draft web layout full screen reading available word online likewise side-by-side viewing split windows available word online excel online execute macros revision support color cells outside default palette supported web browsers include microsoft edge internet explorer 11 latest versions firefox google chrome well safari os x 10.8 later personal edition office online available general public free charge microsoft account office.com website superseded skydrive onedrive office live workspace enterprise-managed versions available office 365 february 2013 ability view edit files skydrive without signing added service also installed privately enterprise environments sharepoint app office web apps server microsoft also offers web apps office suite outlook web app formerly outlook web access lync web app formerly office communicator web access project web app formerly project web access additionally microsoft offers service name online doc viewer view office documents website via office online google chrome extension free available use office online directly
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Distributed computing architecture
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u-prove u-prove microsoft technology user-centric identity management underlying cryptographic protocols designed dr. stefan brands developed credentica subsequently microsoft u-prove enables application developers reconcile seemingly conflicting security privacy objectives including anonymity allows digital identity claims efficiently tied use tamper-resistant devices smart cards application areas particular interest include cross-domain enterprise identity access management e-government sso data sharing electronic health records anonymous electronic voting policy-based digital rights management social networking data portability electronic payments 2008 microsoft committed opening u-prove technology first step march 2010 company released cryptographic specification open-source api implementation code part u-prove technology community technology preview microsoft open specification promise since several extensions released terms technology tested real-life applications
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Operating systems
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member variable object-oriented programming member variable sometimes called member field variable associated specific object accessible methods member functions class-based languages distinguished two types one copy variable shared instances class called class variable static member variable instance class copy variable variable called instance variable class foo int main public class program public class foo class foo f foo f.bar 100 print f.bar
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Programming language topics
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zonealarm zonealarm internet security software company provides consumer antivirus firewall products zonealarm developed zone labs acquired march 2004 check point zonealarm firewall security products include inbound intrusion detection system well ability control programs create outbound connections august 2015 zonealarm introduced 100 virus-free guarantee extreme security product zonealarm program access controlled way zones network connections divided trusted zone generally includes user local area network share resources files printers internet zone includes everything trusted zone user specify permissions trusted zone client trusted zone server internet zone client internet zone server give program attempts access internet e.g running first time alternatively zonealarm ask user give program permission first access attempt true vector internet monitor also known truevector security engine windows service core zonealarm processes list image name vsmon.exe monitors internet traffic generates alerts disallowed access operating system firewall osfirewall monitors programs generates alerts perform suspicious behaviors osfirewall useful preventing rootkits spyware smartdefense advisor name zonealarm give service available versions helps user certain types alert using database trusted program signatures provide user advice allowing denying internet access response program requests current free version zonealarm ad paid version pops every single time turn computer short delay free pro editions zonealarm firewall designated pcmag editor ’ choice 2017 january 2006 zonealarm reportedly sending data company servers covert fashion developer dismissed allegations zonealarm spying clients saying issue related software updates would fixed december 2007 browser toolbar shipped zonealarm opt-out well received removed later versions software september 2 2010 free version zonealarm started showing global virus alert popup scareware tactic get users switch paid security suite popup turned zonealarm marketing team uproar disgruntled users many uninstalled software
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Computer security
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gnu privacy guard gnu privacy guard gnupg gpg free-software replacement symantec pgp cryptographic software suite compliant rfc 4880 ietf standards-track specification openpgp modern versions pgp interoperable gnupg openpgp-compliant systems gnupg part gnu project received major funding german government gnupg hybrid-encryption software program uses combination conventional symmetric-key cryptography speed public-key cryptography ease secure key exchange typically using recipient public key encrypt session key used mode operation part openpgp standard part pgp first version gnupg 1.x series uses integrated cryptographic library gnupg 2.x series replaces libgcrypt gnupg encrypts messages using asymmetric key pairs individually generated gnupg users resulting public keys may exchanged users variety ways internet key servers must always exchanged carefully prevent identity spoofing corrupting public key ↔ owner identity correspondences also possible add cryptographic digital signature message message integrity sender verified particular correspondence relied upon corrupted gnupg also supports symmetric encryption algorithms default gnupg uses aes symmetrical algorithm since version 2.1 cast5 used earlier versions gnupg use patented otherwise restricted software algorithms instead gnupg uses variety non-patented algorithms long time support idea encryption algorithm used pgp fact possible use idea gnupg downloading plugin however might require license uses countries idea patented starting versions 1.4.13 2.0.20 gnupg supports idea last patent idea expired 2012 support idea intended get rid questions folks either trying decrypt old data migrating keys pgp gnupg hence recommended regular use versions 2.0.26 1.4.18 gnupg supports following algorithms recent releases gnupg 2.x modern deprecated stable series expose cryptographic functions algorithms libgcrypt cryptography library provides including support elliptic curve cryptography ecdsa ecdh eddsa modern series i.e since gnupg 2.1 gnupg initially developed werner koch first production version version 1.0.0 released september 7 1999 almost two years first gnupg release version 0.0.0 german federal ministry economics technology funded documentation port microsoft windows 2000 gnupg system compliant openpgp standard thus history openpgp importance designed interoperate pgp email encryption program initially designed developed phil zimmermann february 7 2014 gnupg crowdfunding effort closed raising €36,732 new web site infrastructure improvements two actively maintained branches gnupg different gnupg 2.x versions e.g 2.2 2.0 branches installed time however possible install classic gnupg version i.e 1.4 branch along gnupg 2.x version release gnupg 2.2 modern deprecated stable branch 2.0 recommended general use initially released november 13 2006 branch reached end-of-life december 31 2017 last version 2.0.31 released december 29 2017 release gnupg 2.0 stable releases originated single branch i.e. november 13 2006 multiple release branches maintained parallel former sequentially succeeding 1.4 release branches although basic gnupg program command-line interface exists various front-ends provide graphical user interface example gnupg encryption support integrated kmail evolution graphical email clients found kde gnome popular linux desktops also graphical gnupg front-ends example seahorse gnome kgpg kde gpg suite project provides number aqua front-ends os integration encryption key management well gnupg installations via installer packages macos furthermore gpg suite installer installs related openpgp applications gpg keychain access plugins gpgmail dependencies macgpg use gnupg based encryption instant messaging applications psi fire automatically secure messages gnupg installed configured web-based software horde also makes use cross-platform extension enigmail provides gnupg support mozilla thunderbird seamonkey similarly enigform provides gnupg support mozilla firefox firegpg discontinued june 7 2010 2005 g10 code gmbh intevation gmbh released gpg4win software suite includes gnupg windows gnu privacy assistant gnupg plug-ins windows explorer outlook tools wrapped standard windows installer making easier gnupg installed used windows systems command-line-based system gnupg 1.x written api may incorporated software overcome gpgme abbreviated gnupg made easy created api wrapper around gnupg parses output gnupg provides stable maintainable api components currently requires out-of-process call gnupg executable many gpgme api calls result possible security problems application propagate actual crypto code due process barrier various graphical front-ends based gpgme created since gnupg 2.0 many gnupg functions available directly c apis libgcrypt openpgp standard specifies several methods digitally signing messages 2003 due error change gnupg intended make one methods efficient security vulnerability introduced affected one method digitally signing messages releases gnupg 1.0.2 1.2.3 fewer 1000 keys listed key servers people use method case discouraged damage caused since none publicly reported would appear minimal support method removed gnupg versions released discovery 1.2.4 later two vulnerabilities discovered early 2006 first scripted uses gnupg signature verification may result false positives second non-mime messages vulnerable injection data covered digital signature would reported part signed message cases updated versions gnupg made available time announcement june 2017 vulnerability cve-2017-7526 discovered within libgcrypt bernstein breitner others library used gnupg enabled full key recovery rsa-1024 1/8th rsa-2048 keys side-channel attack exploits fact libgcrypt used sliding windows method exponentiation leads leakage exponent bits full key recovery updated version gnupg made available time announcement october 2017 roca vulnerability announced affects rsa keys generated yubikey 4 tokens often used pgp/gpg many published pgp keys found susceptible around june 2018 sigspoof attacks announced allowed attacker convincingly spoof digital signatures notable applications front ends browser extensions support gpg include following may 2014 washington post reported 12-minute video guide gpg journalists posted vimeo january 2013 user named anon108 post identified anon108 fugitive nsa whistleblower edward snowden said made tutorial — narrated digitally disguised voice whose speech patterns sound similar snowden — teach journalist glenn greenwald email encryption greenwald said could confirm authorship video
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Computer security
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snapshot computer storage computer systems snapshot state system particular point time term coined analogy photography refer actual copy state system capability provided certain systems full backup large data set may take long time complete multi-tasking multi-user systems may writes data backed prevents backup atomic introduces version skew may result data corruption example user moves file directory already backed file would completely missing backup media since backup operation already taken place addition file version skew may also cause corruption files change size contents underfoot read one approach safely backing live data temporarily disable write access data backup either stopping accessing applications using locking api provided operating system enforce exclusive read access tolerable low-availability systems desktop computers small workgroup servers regular downtime acceptable high-availability 24/7 systems however bear service stoppages avoid downtime high-availability systems may instead perform backup snapshot —a read-only copy data set frozen point time—and allow applications continue writing data snapshot implementations efficient create snapshots 1 words time i/o needed create snapshot increase size data set contrast time i/o required direct backup proportional size data set systems initial snapshot taken data set subsequent snapshots copy changed data use system pointers reference initial snapshot method pointer-based snapshots consumes less disk capacity data set repeatedly cloned unix systems snapshot-capable logical volume managers implement copy-on-write entire block devices copying changed blocksjust overwritten within parent volumesto storage thus preserving self-consistent past image block device filesystems snapshot images later mounted read-only media volume managers also allow creation writable snapshots extending copy-on-write approach disassociating blocks modified within snapshot parent blocks original volume scheme could also described performing additional copy-on-write operations triggered writes snapshots linux logical volume manager lvm allows creation read-only read-write snapshots writable snapshots introduced lvm version 2 lvm2 file systems wafl fossil plan 9 bell labs ods-5 internally track old versions files make snapshots available special namespace others like ufs2 provide operating system api accessing file histories ntfs access snapshots provided volume shadow-copying service vss windows xp windows server 2003 shadow copy windows vista melio fs provides snapshots via vss interface shared storage snapshots also available nss novell storage services file system netware since version 4.11 recently linux platforms open enterprise server product emc isilon onefs clustered storage platform implements single scalable file system supports read-only snapshots file directory level file directory within file system snapshotted system implement copy-on-write point-in-time snapshot dynamically based method determined optimal system linux btrfs ocfs2 file systems support creating snapshots cloning individual files additionally btrfs also supports creation snapshots subvolumes aix jfs2 also support snapshots sun microsystems zfs hybrid implementation tracks read-write snapshots block level makes branched file sets nameable user applications clones time machine included apple mac os x v10.5 operating system snapshotting scheme system-level incremental backup service merely watches mounted volumes changes copies changed files periodically specially-designated volume using hard links ancient hfs plus file system n't snapshotting feature apple new apfs file system introduces feature
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Computer architecture
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beeline software company beeline software-as-a-service company dealing solutions sourcing managing extended workforce company ranks among largest vendor management system vms providers terms total temp/contract spend outsourced spend staffing industry analysts 2017 vms markets development summary report beeline founded 1999 workforce solutions business unit mps group inc. jacksonville florida company among first offer vms solutions december 2016 chicago-based private equity firm gtcr acquired beeline merged company iqnavigator previously competitor workforce management solutions marketplace merged company operates beeline brand name march 2017 beeline named leader “ contingent workers consulting services ” forrester wave services procurement q1 2017 report forrester research inc. gartner inc. ranked beeline first statement work procurement critical capabilities services procurement solutions report july 2018 beeline announced acquired new mountain capital new york city-based private equity firm undisclosed amount beeline collaborates number partner organizations including talent providers enterprise software solution providers managed services providers msps strategic msp partners include allegis global solutions hayes talent solutions kellyocg pontoon
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Distributed computing architecture
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