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homeland open security technology homeland open security technology host five-year 10 million program department homeland security science technology directorate promote creation use open security open-source software united states government military especially areas pertaining computer security proponent david a. wheeler claims open-source security could also extend hardware written documents october 2011 project open source america 2011 government deployment open source award project contracted open technology research consortium consists georgia tech research institute primary center agile technology university texas austin open source software institute open information security foundation project contributed funding towards openssl software foundation open information security foundation october 2012 host hosted open cybersecurity summit washington d.c. one-day summit keynote stewart a. baker former assistant secretary policy department homeland security
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Computer security
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iad iad discontinued mobile advertising platform developed apple inc. iphone ipod touch ipad line mobile devices allowing third-party developers directly embed advertisements applications announced april 8 2010 iad part apple ios 4 originally slated release june 21 2010 actual date changed july 1 2010. iad announced apple june 7 2010 keynote ipad version appearing fall hosted sold apple iad platform expected compete google admob mobile advertising service similar admob iad facilitates integrating advertisements applications sold ios app store user tapped iad banner full-screen advertisement appeared within application unlike ads would send user safari web browser ads promised interactive advertising services users able close time returning left app former apple ceo steve jobs initially indicated apple would retain 40 ad revenue line called industry standard 60 going developers amount paid developers later increased 70 iad expected benefit free applications well iad app network discontinued june 30 2016 since technology lives apple news advertising app store search ads
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Operating systems
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hypertable hypertable open-source software project implement database management system inspired publications design google bigtable hypertable runs top distributed file system apache hdfs glusterfs cloudstore kosmos file system kfs written almost entirely c++ developers believed significant performance advantages java hypertable software originally developed company zvents 2008 doug judd promoter hypertable january 2009 baidu chinese language search engine became project sponsor version 0.9.2.1 described blog february 2009 development ended march 2016
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Databases
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information security awareness information security awareness evolving part information security focuses raising consciousness regarding potential risks rapidly evolving forms information rapidly evolving threats information target human behavior threats matured information increased value attackers increased capabilities expanded broader intentions developed attack methods methodologies acting diverse motives information security controls processes matured attacks matured circumvent controls processes attackers targeted successfully exploited individuals human behavior breach corporate networks critical infrastructure systems targeted individuals unaware information threats may unknowingly circumvent traditional security controls processes enable breach organization response information security awareness maturing cybersecurity business problem dominated agenda chief information officers cio exposing need countermeasures today cyber threat landscape goal information security awareness make everyone aware susceptible opportunities challenges today ’ threat landscape change human risk behaviors create enhance secure organizational culture information security awareness one several key principles information security information security awareness seeks understand enhance human risk behaviors beliefs perceptions information information security also understanding enhancing organizational culture countermeasure rapidly evolving threats example oecd guidelines security information systems networks include nine generally accepted principles awareness responsibility response ethics democracy risk assessment security design implementation security management reassessment context internet type awareness sometimes referred cyber security awareness focus multiple initiatives including u.s. department homeland security national cyber security awareness month president obama 2015 white house summit cybersecurity consumer protection computer based crimes something new us viruses us well 20 years spyware clocked decade since earliest incidents large-scale use phishing traced back least 2003 one reasons researchers agreed upon pace information system evolving expanding security awareness program among employees falling way behind unfortunately however seems rapid adoption online services matched corresponding embrace security culture information security awareness evolving response evolving nature cyber attacks increased targeting personal information cost scale information security breaches furthermore many individuals think security terms technical controls realizing individuals targets behavior increase risks provide countermeasures risks threats determining measuring information security awareness highlighted need accurate metrics response need information security awareness metrics rapidly evolving order understand measure human threat landscape measure change human understanding behavior measure reduce organizational risk measure effectiveness cost information security awareness countermeasure organizations want invest money information security survey conducted pricewaterhousecoopers 2014 found current employees 31 former employees 27 still contribute information security incidents survey results indicated number actual incidents attributable employees risen 25 since 2013 survey security awareness program best solution organization adopt reduce security threats caused internal employees security awareness program helps employees understand information security individual ’ responsibility responsibility everyone program also explicitly mentions employees responsible activities performed identifications furthermore program enforces standard ways handling business computers although organizations adopted standard way providing security awareness program good program include awareness data network user conduct social media use mobile devices wifi phishing emails social engineering different types viruses malware effective employee security awareness program make clear everyone organization responsible security auditors pay close attention six areas covered program data networks user conduct social media mobile devices social engineering many organizations make privacy policies complicated diverse employees always fail understand regulations privacy policy something reminded employees whenever login business computer privacy policies clearer shorter standardized enable better comprehension comparison privacy practices organizations create interactive sessions employees attend every week speak security threats interactive sessions may include awareness newer threats best practices questions answers security awareness program may beneficial organization penalize violators employees found guilty violating program reported higher executives action otherwise program effective information security authorities may perform gap analysis find deficiencies program early 2015 cios rated information security awareness related issues top strategic priorities example february 2015 wall street journal cio network event convened create prioritized set recommendations drive business policy coming year consensus seemed form around cybersecurity delivering change effective communication rest business information security awareness high-profile breaches forefront organization agenda recent study 220 security awareness officers lance spritzner uncovered three related key findings first executive financial support necessary successful security awareness program second due technical nature traditional security controls countermeasures soft skills necessary understand change human behavior lacking finally terms maturity model security awareness still infancy effectively measuring human risk behavior difficult risky behaviors beliefs perceptions often unknown addition attacks phishing social engineering incidents data leakage sensitive data posted social media sites even breaches go undetected unknown making difficult determine measure points failure often attacks incidents breaches reacted reported outside compromised organization attackers covered tracks thus researched measured proactively addition malicious traffic often goes unnoticed attackers often spy mimic known behavior order prevent intrusion detection access monitoring alerts 2016 study developed method measuring security awareness specifically measured understanding circumventing security protocols disrupting intended functions systems collecting valuable information getting caught p. 38 researchers created method could distinguish experts novices people organize different security scenarios groups experts organize scenarios based centralized security themes novices organize scenarios based superficial themes simulated phishing campaigns run regularly provide measures user compliance
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Computer security
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liquibase liquibase open-source database-independent library tracking managing applying database schema changes started 2006 allow easier tracking database changes especially agile software development environment changes database stored text files xml yaml json sql identified combination id author tag well name file list applied changes stored database consulted database updates determine new changes need applied result database version number approach allows work environments multiple developers code branches liquibase automatically creates databasechangelog table databasechangeloglock table first execute changelog file datical largest contributor liquibase project developer datical db – commercial product provides core liquibase functionality plus additional features datical db used dbas release managers devops teams application owners architects developers involved application release process manages database schema changes together application code programmatic fashion eliminates errors delays enables rapid agile releases datical db builds upon liquibase data model approach managing data structure specific content across application versions advance development test production environments datical previews impact schema changes environment deployment thus mitigating risk resulting smoother faster application changes liquibase developer nathan voxland executive datical
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Databases
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mesa programming language mesa programming language developed late 1970s xerox palo alto research center palo alto california united states language name pun based upon programming language catchphrases time mesa high level programming language mesa algol-like language strong support modular programming every library module least two source files definitions file specifying library interface plus one program files specifying implementation procedures interface use library program higher-level library must import definitions mesa compiler type-checks uses imported entities combination separate compilation type-checking unusual time mesa introduced several innovations language design implementation notably handling software exceptions thread synchronization incremental compilation mesa developed xerox alto one first personal computers graphical user interface however alto system software written bcpl mesa system programming language later xerox star workstations globalview desktop environment xerox parc later developed cedar superset mesa mesa cedar major influence design important languages modula-2 java important vehicle development dissemination fundamentals guis networked environments advances xerox contributed field computer science mesa originally designed computer systems laboratory csl branch xerox palo alto research center alto experimental micro-coded workstation initially spread confined parc universities xerox donated altos mesa later adopted systems programming language xerox commercial workstations xerox 8010 xerox star dandelion xerox 6085 daybreak particular pilot operating system secondary development environment called xerox development environment xde allowed developers debug operating system pilot well viewpoint gui applications using world swap mechanism allowed entire state world swapped allowed low level system crashes paralyzed whole system debugged technique scale well large application images several megabytes pilot/mesa world later releases moved away world swap view micro-coded machines phased favor sparc workstations intel pcs running mesa princops emulator basic hardware instruction set mesa compiled stack-machine language purportedly highest code density ever achieved roughly 4 bytes per high-level language statement touted 1981 paper implementors xerox systems development department development arm parc tuned instruction set published paper resultant code density mesa taught via mesa programming course took people wide range technology xerox available time ended programmer writing hack workable program designed useful actual example hack bwsmagnifier written 1988 allowed people magnify sections workstation screen defined resizable window changeable magnification factor trained mesa programmers xerox well versed fundamental guis networking exceptions multi-threaded programming almost decade became standard tools trade within xerox mesa eventually superseded cedar programming language many mesa programmers developers left xerox 1985 went dec systems research center used experience mesa design modula-2+ later modula-3 mesa strongly typed programming language type-checking across module boundaries enough flexibility type system heap allocators could written mesa strict separation interface implementation mesa allows true incremental compilation encourages architecture- platform-independent programming also simplified source-level debugging including remote debugging via ethernet mesa rich exception handling facilities four types exceptions support thread synchronization via monitors mesa first language implement monitor broadcast concept introduced pilot operating system mesa imperative algebraic syntax based algol pascal rather bcpl c instance compound commands indicated keywords rather braces mesa keywords written uppercase due peculiarity ascii variant used parc alto character set included left-pointing arrow ← rather underscore result alto programmers including using mesa smalltalk etc conventionally used camelcase compound identifiers practice incorporated parc standard programming style hand availability left-pointing arrow allowed use assignment operator originally algol mesa designers wanted implement exception facility hired recent m.s graduate colorado written thesis exception handling facilities algorithmic languages led richest exception facility time primitives language type-safe checks verify full coverage signal handling uncaught exceptions common cause bugs released software xerox parc later developed cedar superset mesa number additions including garbage collection better string support called ropes later native compiler sun sparc workstations importantly cedar contained type-safe subset compiler subset-checking mode ensure deterministic execution memory leaks conformant cedar code mesa precursor programming language cedar cedar main additions garbage collection dynamic types limited form type parameterization special syntax identify type-safe parts multi-module software package
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Programming language topics
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apache calcite apache calcite open source framework building databases data management systems includes sql parser api building expressions relational algebra query planning engine framework calcite store data metadata instead allows external data metadata accessed means plug-ins several apache projects use calcite hive uses calcite cost-based query optimization drill kylin use calcite sql parsing optimization samza storm use calcite streaming sql apex phoenix flink projects development use calcite
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Databases
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hashkeeper hashkeeper database application value primarily conducting forensic examinations computers somewhat regular basis hashkeeper uses md5 file signature algorithm establish unique numeric identifiers hash values files known good known bad hashkeeper application developed reduce amount time required examine files digital media examiner defines file known good examiner need repeat analysis hashkeeper compares hash values known good files hash values files computer system values match known good files examiner say substantial certainty corresponding files computer system previously identified known good therefore need examined values match known bad files examiner say substantial certainty corresponding files system examined files bad therefore require scrutiny hash match known bad files relieve examiner responsibility verifying file files fact criminal nature created national drug intelligence center ndic —a component united states department justice—in 1996 first large scale source hash values known good known bad files hashkeeper still community effort based upon belief members state national international law enforcement agencies trusted submit properly categorized hash values one first community sources known good hash values united states internal revenue service first source known bad hash values luxembourg police contributed hash values recognized child pornography hashkeeper available free-of-charge law enforcement military government agencies throughout world available public sending freedom information act request ndic 2012 united states budget ndic de-funded closed doors june 16 2012 availability future hashkeeper uncertain hashkeeper overview national drug intelligence center http //www.justice.gov/archive/ndic/ndic-moved.html http //www.nsrl.nist.gov/nsrl-faqs.html faq12
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Computer security
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interpolation attack cryptography interpolation attack type cryptanalytic attack block ciphers two attacks differential cryptanalysis linear cryptanalysis presented block ciphers new block ciphers introduced proven secure differential linear attacks among iterated block ciphers kn-cipher shark cipher however thomas jakobsen lars knudsen showed late 90 ciphers easy break introducing new attack called interpolation attack attack algebraic function used represent s-box may simple quadratic polynomial rational function galois field coefficients determined standard lagrange interpolation techniques using known plaintexts data points alternatively chosen plaintexts used simplify equations optimize attack simplest version interpolation attack expresses ciphertext polynomial plaintext polynomial relative low number unknown coefficients collection plaintext/ciphertext p/c pairs polynomial reconstructed polynomial reconstructed attacker representation encryption without exact knowledge secret key interpolation attack also used recover secret key easiest describe method example let iterated cipher given formula_2 plaintext formula_3 output formula_4 round formula_5 secret formula_4 round key derived secret key formula_7 key schedule formula_8-round iterated cipher formula_9 ciphertext consider 2-round cipher let formula_10 denote message formula_11 denote ciphertext output round 1 becomes output round 2 becomes expressing ciphertext polynomial plaintext yields formula_16 key dependent constants using many plaintext/ciphertext pairs number unknown coefficients polynomial formula_17 construct polynomial example done lagrange interpolation see lagrange polynomial unknown coefficients determined representation formula_17 encryption without knowledge secret key formula_7 considering formula_20-bit block cipher formula_21 possible plaintexts therefore formula_21 distinct formula_23 pairs let formula_24 unknown coefficients formula_17 since require many formula_23 pairs number unknown coefficients polynomial interpolation attack exist formula_27 assume time construct polynomial formula_17 using formula_23 pairs small comparison time encrypt required plaintexts let formula_24 unknown coefficients formula_17 time complexity attack formula_24 requiring formula_24 known distinct formula_23 pairs often method efficient done given formula_8 round iterated cipher block length formula_20 let formula_37 output cipher formula_38 rounds formula_39 express value formula_37 polynomial plaintext formula_10 polynomial ciphertext formula_11 let formula_43 expression formula_37 via formula_10 let formula_46 expression formula_37 via formula_11 polynomial formula_49 obtain computing forward using iterated formula cipher round formula_38 polynomial formula_51 obtain computing backwards iterated formula cipher starting round formula_8 round formula_53 hold formula_55 formula_56 polynomials low number coefficients solve equation unknown coefficients assume formula_49 expressed formula_58 coefficients formula_51 expressed formula_60 coefficients would need formula_61 known distinct formula_23 pairs solve equation setting matrix equation however matrix equation solvable multiplication addition make sure get unique non-zero solution set coefficient corresponding highest degree one constant term zero therefore formula_63 known distinct formula_23 pairs required time complexity attack formula_63 requiring formula_63 known distinct formula_23 pairs meet-in-the-middle approach total number coefficients usually smaller using normal method makes method efficient since less formula_23 pairs required also use interpolation attack recover secret key formula_7 remove last round formula_8-round iterated cipher block length formula_20 output cipher becomes formula_72 call cipher reduced cipher idea make guess last round key formula_73 decrypt one round obtain output formula_74 reduced cipher verify guess use interpolation attack reduced cipher either normal method meet-in-the-middle method done normal method express output formula_74 reduced cipher polynomial plaintext formula_10 call polynomial formula_77 express formula_17 formula_24 coefficients using formula_24 known distinct formula_23 pairs construct polynomial verify guess last round key check one extra formula_23 pair holds yes high probability guess last round key correct make another guess key meet-in-the-middle method express output formula_37 round formula_39 polynomial plaintext formula_10 polynomial output reduced cipher formula_74 call polynomials formula_49 formula_89 let expressed formula_58 formula_60 coefficients respectively formula_92 known distinct formula_23 pairs find coefficients verify guess last round key check one extra formula_23 pair holds yes high probability guess last round key correct make another guess key found correct last round key continue similar fashion remaining round keys secret round key length formula_20 formula_21 different keys probability formula_98 correct chosen random therefore average make formula_99 guesses finding correct key hence normal method average time complexity formula_100 requiring formula_101 known distinct formula_102 pairs meet-in-the-middle method average time complexity formula_103 requiring formula_104 known distinct formula_102 pairs meet-in-the-middle attack used variant attack s-boxes uses inverse function formula_20-bit s-box formula_107 formula_108 block cipher shark uses sp-network s-box formula_109 cipher resistant differential linear cryptanalysis small number rounds however broken 1996 thomas jakobsen lars knudsen using interpolation attack denote sharkformula_110 version shark block size formula_111 bits using formula_24 parallel formula_20-bit s-boxes formula_8 rounds jakobsen knudsen found exist interpolation attack sharkformula_115 64-bit block cipher using formula_116 chosen plaintexts interpolation attack sharkformula_117 128-bit block cipher using formula_118 chosen plaintexts also thomas jakobsen introduced probabilistic version interpolation attack using madhu sudan algorithm improved decoding reed-solomon codes attack work even algebraic relationship plaintexts ciphertexts holds fraction values
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Computer security
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smf 120.9 smf 120 subtype 9 new smf record made available ibm websphere application server z/os version 7 design based customer feedback regarding data required operating z/os previous z/os smf records subtypes 1 3 5 6 7 8 subtypes continue exist subtype 9 may viewed replacement shorthand way referring smf 120 subtype 9 smf 120.9 smf 120.9 provided address two shortcomings previous smf design z/os smf 120.9 activity record based per request design longer need correlate data points across records determine statistical information per request information contained smf 120.9 record contains data request overhead turning smf 120.9 measured approximately 1.5 system cpu basic activity records smf 120.9 record divided ten sections section number fields containing specific information request sections optional may turned based administrator need information ibm information center link referenced mapping sections data fields description data represents wp101342 techdoc referenced extensive description feature written architect developer new function z/os operating system allows started tasks modified operator command allows behavior started task dynamically altered degree modification permitted function started task program limits environment format modify command codice_1 z/os modify issued controller jobname smf 120.9 function z/os supports modify command following parameters sample java program available evaluate dumped smf 120.9 records provide detailed summary view information contain may obtained link registration required sample smf browser called intended replacement powerful smf record analysis products useful seeing format records verifying records written smaller scale analysis br
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Operating systems
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system information mac system information previously known system profiler software utility derived field service diagnostics produced apple service diagnostic engineering team time located apple satellite buildings campbell california bundled classic mac os since mac os 7.6 name apple system profiler mac os x v10.0 first release macos renamed system profiler release mac os x 10.7 lion renamed system information new features lion ability look support information user hardware model well os x mountain lion later versions macos users also access system information holding option key system information ... replace mac apple menu compiles technical information installed hardware devices drivers applications system settings system software programs kernel extensions installed host computer export information plain text rtf plist xml format information used diagnose problems system profiler extremely useful attempting diagnose hardware problem user send information directly apple user desires support scripting automation applescript limited support automator system information also accessed using system_profiler command terminal application information execute man system_profiler system_profiler -h macos terminal application
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Operating systems
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machine translation machine translation sometimes referred abbreviation mt confused computer-aided translation machine-aided human translation maht interactive translation sub-field computational linguistics investigates use software translate text speech one language another basic level mt performs simple substitution words one language words another alone usually produce good translation text recognition whole phrases closest counterparts target language needed solving problem corpus statistical neural techniques rapidly growing field leading better translations handling differences linguistic typology translation idioms isolation anomalies current machine translation software often allows customization domain profession weather reports improving output limiting scope allowable substitutions technique particularly effective domains formal formulaic language used follows machine translation government legal documents readily produces usable output conversation less standardised text improved output quality also achieved human intervention example systems able translate accurately user unambiguously identified words text proper names assistance techniques mt proven useful tool assist human translators limited number cases even produce output used e.g. weather reports progress potential machine translation debated much history since 1950s number scholars questioned possibility achieving fully automatic machine translation high quality first notably yehoshua bar-hillel critics claim in-principle obstacles automating translation process idea machine translation may traced back 17th century 1629 rené descartes proposed universal language equivalent ideas different tongues sharing one symbol field machine translation appeared warren weaver memorandum translation 1949 first researcher field yehosha bar-hillel began research mit 1951 georgetown university mt research team followed 1951 public demonstration georgetown-ibm experiment system 1954 mt research programs popped japan russia 1955 first mt conference held london 1956 researchers continued join field association machine translation computational linguistics formed u.s. 1962 national academy sciences formed automatic language processing advisory committee alpac study mt 1964 real progress much slower however alpac report 1966 found ten-year-long research failed fulfill expectations funding greatly reduced according 1972 report director defense research engineering ddr e feasibility large-scale mt reestablished success logos mt system translating military manuals vietnamese conflict french textile institute also used mt translate abstracts french english german spanish 1970 brigham young university started project translate mormon texts automated translation 1971 xerox used systran translate technical manuals 1978 beginning late 1980s computational power increased became less expensive interest shown statistical models machine translation various mt companies launched including trados 1984 first develop market translation memory technology 1989 first commercial mt system russian english german-ukrainian developed kharkov state university 1991 mt web started systran offering free translation small texts 1996 followed altavista babelfish racked 500,000 requests day 1997 franz josef och future head translation development google darpa speed mt competition 2003 innovations time included moses open-source statistical mt engine 2007 text/sms translation service mobiles japan 2008 mobile phone built-in speech-to-speech translation functionality english japanese chinese 2009 recently google announced google translate translates roughly enough text fill 1 million books one day 2012 idea using digital computers translation natural languages proposed early 1946 a. d. booth possibly others warren weaver wrote important memorandum translation 1949 georgetown experiment means first application demonstration made 1954 apexc machine birkbeck college university london rudimentary translation english french several papers topic published time even articles popular journals example article cleave zacharov september 1955 issue wireless world similar application also pioneered birkbeck college time reading composing braille texts computer human translation process may described behind ostensibly simple procedure lies complex cognitive operation decode meaning source text entirety translator must interpret analyse features text process requires in-depth knowledge grammar semantics syntax idioms etc. source language well culture speakers translator needs in-depth knowledge re-encode meaning target language therein lies challenge machine translation program computer understand text person create new text target language sounds written person general application beyond current technology though works much faster automated translation program procedure human participation produce output even close quality human translator produce however provide general though imperfect approximation original text getting gist process called gisting sufficient many purposes including making best use finite expensive time human translator reserved cases total accuracy indispensable problem may approached number ways evolution accuracy improved machine translation use method based linguistic rules means words translated linguistic way – suitable orally speaking words target language replace ones source language often argued success machine translation requires problem natural language understanding solved first generally rule-based methods parse text usually creating intermediary symbolic representation text target language generated according nature intermediary representation approach described interlingual machine translation transfer-based machine translation methods require extensive lexicons morphological syntactic semantic information large sets rules given enough data machine translation programs often work well enough native speaker one language get approximate meaning written native speaker difficulty getting enough data right kind support particular method example large multilingual corpus data needed statistical methods work necessary grammar-based methods grammar methods need skilled linguist carefully design grammar use translate closely related languages technique referred rule-based machine translation may used rule-based machine translation paradigm includes transfer-based machine translation interlingual machine translation dictionary-based machine translation paradigms type translation used mostly creation dictionaries grammar programs unlike methods rbmt involves information linguistics source target languages using morphological syntactic rules semantic analysis languages basic approach involves linking structure input sentence structure output sentence using parser analyzer source language generator target language transfer lexicon actual translation rbmt biggest downfall everything must made explicit orthographical variation erroneous input must made part source language analyser order cope lexical selection rules must written instances ambiguity adapting new domains hard core grammar across domains domain-specific adjustment limited lexical selection adjustment transfer-based machine translation similar interlingual machine translation creates translation intermediate representation simulates meaning original sentence unlike interlingual mt depends partially language pair involved translation interlingual machine translation one instance rule-based machine-translation approaches approach source language i.e text translated transformed interlingual language i.e language neutral representation independent language target language generated interlingua one major advantages system interlingua becomes valuable number target languages turned increases however interlingual machine translation system made operational commercial level kant system nyberg mitamura 1992 designed translate caterpillar technical english cte languages machine translation use method based dictionary entries means words translated dictionary statistical machine translation tries generate translations using statistical methods based bilingual text corpora canadian hansard corpus english-french record canadian parliament europarl record european parliament corpora available good results achieved translating similar texts corpora still rare many language pairs first statistical machine translation software candide ibm google used systran several years switched statistical translation method october 2007 2005 google improved internal translation capabilities using approximately 200 billion words united nations materials train system translation accuracy improved google translate similar statistical translation programs work detecting patterns hundreds millions documents previously translated humans making intelligent guesses based findings generally human-translated documents available given language likely translation good quality newer approaches statistical machine translation metis ii presemt use minimal corpus size instead focus derivation syntactic structure pattern recognition development may allow statistical machine translation operate monolingual text corpus smt biggest downfall includes dependent upon huge amounts parallel texts problems morphology-rich languages especially translating languages inability correct singleton errors example-based machine translation ebmt approach proposed makoto nagao 1984 example-based machine translation based idea analogy approach corpus used one contains texts already translated given sentence translated sentences corpus selected contain similar sub-sentential components similar sentences used translate sub-sentential components original sentence target language phrases put together form complete translation hybrid machine translation hmt leverages strengths statistical rule-based translation methodologies several mt organizations claim hybrid approach uses rules statistics approaches differ number ways recently advent neural mt new version hybrid machine translation emerging combines benefits rules statistical neural machine translation approach allows benefitting pre- post-processing rule guided workflow well benefitting nmt smt downside inherent complexity makes approach suitable specific use cases one proponents approach complex use cases omniscien technologies deep learning based approach mt neural machine translation made rapid progress recent years google announced translation services using technology preference previous statistical methods word-sense disambiguation concerns finding suitable translation word one meaning problem first raised 1950s yehoshua bar-hillel pointed without universal encyclopedia machine would never able distinguish two meanings word today numerous approaches designed overcome problem approximately divided shallow approaches deep approaches shallow approaches assume knowledge text simply apply statistical methods words surrounding ambiguous word deep approaches presume comprehensive knowledge word far shallow approaches successful claude piron long-time translator united nations world health organization wrote machine translation best automates easier part translator job harder time-consuming part usually involves extensive research resolve ambiguities source text grammatical lexical exigencies target language require resolved ideal deep approach would require translation software research necessary kind disambiguation would require higher degree ai yet attained shallow approach simply guessed sense ambiguous english phrase piron mentions based perhaps kind prisoner-of-war camp often mentioned given corpus would reasonable chance guessing wrong fairly often shallow approach involves ask user ambiguity would piron estimate automate 25 professional translator job leaving harder 75 still done human one major pitfalls mt inability translate non-standard language accuracy standard language heuristic statistical based mt takes input various sources standard form language rule-based translation nature include common non-standard usages causes errors translation vernacular source colloquial language limitations translation casual speech present issues use machine translation mobile devices name entities narrow sense refer concrete abstract entities real world including people organizations companies places etc also refers expressing time space quantity 1 july 2011 79.99 named entities occur text analyzed statistical machine translation initial difficulty arises dealing named entities simply identifying text consider list names common particular language illustrate – common names different language also constantly changing named entities recognized machine translator may erroneously translated common nouns would likely affect bleu rating translation would change text human readability also possible identified named entities omitted output translation would also implications text readability message another way deal named entities use transliteration instead translation meaning find letters target language closely correspond name source language attempts incorporate machine translation adding transliteration step translation procedure however attempts still problems even cited worsening quality translation named entities still identified incorrectly words transliterated transliterated n't example southern california first word translated directly second word transliterated however machines would often transliterate treated one entity words like hard machine translators even transliteration component process lack attention issue named entity translation recognized potentially stemming lack resources devote task addition complexity creating good system named entity translation one approach named entity translation transliterate translate words second create do-not-translate list end goal – transliteration opposed translation approaches still rely correct identification named entities however third approach successful named entity translation class-based model method named entities replaced token represent class belong example ted erica would replaced person class token way statistical distribution use person names general analyzed instead looking distributions ted erica individually problem class based model solves probability given name specific language affect assigned probability translation study stanford improving area translation gives examples different probabilities assigned david going walk ankit going walk english target language due different number occurrences name training data frustrating outcome study stanford attempts improve named recognition translation many times decrease bleu scores translation result inclusion methods named entity translation work done utilization multiparallel corpora body text translated 3 languages using methods text translated 2 languages may utilized combination provide accurate translation third language compared one source languages used alone ontology formal representation knowledge includes concepts objects processes etc domain relations stored information linguistic nature one speak lexicon nlp ontologies used source knowledge machine translation systems access large knowledge base systems enabled resolve many especially lexical ambiguities following classic examples humans able interpret prepositional phrase according context use world knowledge stored lexicons machine translation system initially would able differentiate meanings syntax change large enough ontology source knowledge however possible interpretations ambiguous words specific context reduced areas usage ontologies within nlp include information retrieval information extraction text summarization ontology generated pangloss knowledge-based machine translation system 1993 may serve example ontology nlp purposes compiled system provides holy grail fully automatic high-quality machine translation unrestricted text many fully automated systems produce reasonable output quality machine translation substantially improved domain restricted controlled despite inherent limitations mt programs used around world probably largest institutional user european commission project example coordinated university gothenburg received 2.375 million euros project support eu create reliable translation tool covers majority eu languages development mt systems comes time budget cuts human translation may increase eu dependency reliable mt programs european commission contributed 3.072 million euros via isa programme creation mt ec statistical machine translation program tailored administrative needs eu replace previous rule-based machine translation system 2005 google claimed promising results obtained using proprietary statistical machine translation engine statistical translation engine used google language tools arabic english chinese english overall score 0.4281 runner-up ibm bleu-4 score 0.3954 summer 2006 tests conducted national institute standards technology recent focus terrorism military sources united states investing significant amounts money natural language engineering in-q-tel venture capital fund largely funded us intelligence community stimulate new technologies private sector entrepreneurs brought companies like language weaver currently military community interested translation processing languages like arabic pashto dari within languages focus key phrases quick communication military members civilians use mobile phone apps information processing technology office darpa hosts programs like tides babylon translator us air force awarded 1 million contract develop language translation technology notable rise social networking web recent years created yet another niche application machine translation software – utilities facebook instant messaging clients skype googletalk msn messenger etc – allowing users speaking different languages communicate machine translation applications also released mobile devices including mobile telephones pocket pcs pdas etc due portability instruments come designated mobile translation tools enabling mobile business networking partners speaking different languages facilitating foreign language learning unaccompanied traveling foreign countries without need intermediation human translator despite labelled unworthy competitor human translation 1966 automated language processing advisory committee put together united states government quality machine translation improved levels application online collaboration medical field investigated application technology medical settings human translators absent another topic research difficulties arise due importance accurate translations medical diagnoses many factors affect machine translation systems evaluated factors include intended use translation nature machine translation software nature translation process different programs may work well different purposes example statistical machine translation smt typically outperforms example-based machine translation ebmt researchers found evaluating english french translation ebmt performs better concept applies technical documents easily translated smt formal language certain applications however e.g. product descriptions written controlled language dictionary-based machine-translation system produced satisfactory translations require human intervention save quality inspection various means evaluating output quality machine translation systems oldest use human judges assess translation quality even though human evaluation time-consuming still reliable method compare different systems rule-based statistical systems automated means evaluation include bleu nist meteor lepor relying exclusively unedited machine translation ignores fact communication human language context-embedded takes person comprehend context original text reasonable degree probability certainly true even purely human-generated translations prone error therefore ensure machine-generated translation useful human publishable-quality translation achieved translations must reviewed edited human late claude piron wrote machine translation best automates easier part translator job harder time-consuming part usually involves extensive research resolve ambiguities source text grammatical lexical exigencies target language require resolved research necessary prelude pre-editing necessary order provide input machine-translation software output meaningless addition disambiguation problems decreased accuracy occur due varying levels training data machine translating programs example-based statistical machine translation rely vast array real example sentences base translation many sentences analyzed accuracy jeopardized researchers found program trained 203,529 sentence pairings accuracy actually decreases optimal level training data seems 100,000 sentences possibly training data increases number possible sentences increases making harder find exact translation match although concerns machine translation accuracy dr. ana nino university manchester researched advantages utilizing machine translation classroom one pedagogical method called using mt bad model mt bad model forces language learner identify inconsistencies incorrect aspects translation turn individual hopefully possess better grasp language dr. nino cites teaching tool implemented late 1980s end various semesters dr. nino able obtain survey results students used mt bad model well models overwhelmingly students felt observed improved comprehension lexical retrieval increased confidence target language early 2000s options machine translation spoken signed languages severely limited common belief deaf individuals could use traditional translators however stress intonation pitch timing conveyed much differently spoken languages compared signed languages therefore deaf individual may misinterpret become confused meaning written text based spoken language researchers zhao et al 2000 developed prototype called team translation english asl machine completed english american sign language asl translations program would first analyze syntactic grammatical morphological aspects english text following step program accessed sign synthesizer acted dictionary asl synthesizer housed process one must follow complete asl signs well meanings signs entire text analyzed signs necessary complete translation located synthesizer computer generated human appeared would use asl sign english text user works original subject copyright protection scholars claim machine translation results entitled copyright protection mt involve creativity copyright issue derivative work author original work original language lose rights work translated translator must permission publish translation
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Computational linguistics
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extensible name service extensible name service often shortened xns open protocol universal addressing automated data exchange xml-based digital identity architecture development xml 1998 led xns project establishment international non-profit governance organization xns public trust organization xnsorg early 2000 2002 xns specifications contributed xnsorg oasis became part xri extensible resource identifier xdi xri data interchange technical committees together two standards xri xdi form basis formation dataweb xnsorg since evolved xdi.org offers community-based xri/xdi infrastructure
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Internet protocols
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final fantasy vi final fantasy vi released critical acclaim seen landmark title role-playing genre instance ranked 2nd best rpg time ign 2017 snes playstation versions sold 3.48 million copies worldwide date stand-alone game well 750,000 copies part japanese final fantasy collection north american final fantasy anthology final fantasy vi numerous awards considered many one greatest video games time ported tose minor differences sony playstation 1999 nintendo game boy advance 2006 released wii virtual console 2011 nintendo re-released final fantasy vi united states september 2017 part company super nes classic edition game known final fantasy iii first released north america original final fantasy ii final fantasy iii final fantasy v released outside japan time leaving iv second title released outside japan vi third however later localizations use original title like previous final fantasy installments final fantasy vi consists four basic modes gameplay overworld map town dungeon field maps battle screen menu screen overworld map scaled-down version game fictional world player uses direct characters various locations games series three primary means travel across overworld foot chocobo airship plot-driven exceptions enemies randomly encountered field maps overworld traveling foot menu screen player makes decisions characters traveling party equipment wield magic learn configuration gameplay also used track experience points levels game plot develops player progresses towns dungeons town citizens offer helpful information residents item equipment shops later game visiting certain towns activate side-quests dungeons appear variety areas including caves forests buildings dungeons often treasure chests containing rare items available stores dungeons may feature puzzles mazes dungeons requiring player divide characters multiple parties must work together advance dungeon combat final fantasy vi menu-based player selects action list options fight magic item maximum four characters may used battles based series traditional active time battle atb system first featured final fantasy iv system character action bar replenishes rate dependent speed statistic character action bar filled player may assign action addition standard battle techniques character possesses unique special ability example locke possesses ability steal items enemies celes runic ability allows absorb magical attacks cast next turn another element powerful attack substitution occasionally appears character health low similar features appear later final fantasy titles variety different names including limit breaks desperation moves trances overdrives characters rewarded victorious battles experience points money called gil gold piece gp original north american localization characters attain certain amount experience points gain level increases statistics additional player may play battle scenarios control individual characters assigned configuration menu characters final fantasy vi equipped variety weapons armor particular entry powerful accessories known relics weapons armor increase combat capability mostly increasing statistics adding beneficial effects attacks comparison relics variety uses effects almost entirely interchangeable among party members extended sophistication alter basic battle commands exceed normal limitations game systems although final fantasy vi two playable characters start game ability use magic magic may later taught almost playable characters games introduction magicite espers magicite shards contain espers game incarnation series trope summons powerful monstrous beings several recurring series history ifrit shiva bahamut odin besides reappear final fantasy vi approximately two dozen total added later versions game critically game uses setting plot feature heavily around espers remains deceased referred magicite equipped playable characters menu magicite specific set magic spells teach character additionally magicite grant statistical bonus character equipped character gains level finally character equips piece magicite character may summon esper corresponds piece magicite contrast medieval settings featured previous final fantasy titles final fantasy vi set world prominent steampunk influences structure society parallels latter half 19th century opera fine arts serving recurring motifs throughout game level technology comparable second industrial revolution first half game planet referred world balance divided three lush continents northern continent punctuated series mountain ranges southern continent mostly subjugated cruel gestahl empire eastern continent home veldt massive wilderness inhabited monsters world apocalyptic event mid-game transforms planet world ruin withering landmasses fractured numerous islands surrounding larger continent game alludes conflict known war magi occurred one thousand years prior beginning game conflict three quarreling entities known warring triad used innocent humans soldiers transforming enslaved magical beings called espers triad realized wrongdoings freed espers sealed powers inside three stone statues precaution espers sealed statues realm humans concept magic gradually faded myth mankind built society extolling science technology game opening empire taken advantage weakening barrier human esper domains capturing several espers process using espers power source empire created magitek craft combines magic machinery including mechanical infantry infuses humans magical powers empire opposed returners rebel organization seeking free subjugated lands final fantasy vi features fourteen permanent playable characters game main series well several secondary characters briefly controlled player starting character terra branford reserved half-human half-esper girl spent life slave empire thanks mind-controlling device unfamiliar love primary characters include locke cole treasure hunter rebel sympathizer powerful impulse protect women celes chere former general empire joined returners jailed questioning imperial practices edgar roni figaro consummate womanizer king figaro claims allegiance empire secretly supplying aid returners sabin rene figaro edgar independent brother fled royal court hone martial arts skills cyan garamonde loyal knight kingdom doma lost family friends kefka poisoned kingdom water supply setzer gabbiani habitual gambler thrill seeker owner world known airship shadow ninja mercenary offers services empire returners relm arrowny young tough artistic girl magical powers strago magus relm elderly grandfather blue mage gau feral child surviving since infancy veldt mog pike-toting moogle mines narshe umaro savage loyal sasquatch also narshe talked joining returners mog persuasion gogo mysterious fully shrouded master art mimicry main characters game hold significant grudge empire particular kefka palazzo serves one game main antagonists along emperor gestahl clownish kefka became first experimental prototype line magically empowered soldiers called magitek knights rendering insane actions throughout game reflect demented nature supporting character ultros serves recurring villain comic relief handful characters reappeared later games final fantasy sgi short tech demo produced silicon graphics onyx workstation featured polygon-based 3d renderings locke terra shadow town narshe terra participates imperial mission seize powerful esper encased ice upon locating magical reaction occurs terra esper result soldiers accompanying terra killed terra knocked unconscious upon awakening terra informed empire using slave crown control actions crown removed terra remember anything name rare ability use magic unaided terra introduced organization known returners agrees help revolution empire returners learn imperial soldiers led kefka planning another attempt seize frozen esper repelling kefka attack terra experiences another magical reaction frozen esper transforms creature resembling esper flies another continent upon locating terra party confronted esper named ramuh informs group terra may require assistance another esper imprisoned imperial capital city vector vector party attempts rescue several espers however espers already dying magitek experiments choose instead offer lives party transforming magicite group returns terra observes reaction magicite maduin reaction calms terra restores memory reveals half-human half-esper child maduin human woman revelation returners ask terra convince espers join cause travels sealed gate human esper worlds however unbeknownst party empire also uses terra gain access esper world emperor gestahl kefka retrieve statues warring triad raising landmass called floating continent group confronts emperor gestahl kefka floating continent whereupon kefka murders gestahl kefka tampers alignment statues upsets balance magic destroys surface world one year later celes awakens deserted island learns kefka using three statues rule world god-like manner rule causing life slowly wither away celes finds lost comrades decide confront kefka end reign kefka killed statues destroyed magic espers disappear world terra able survive hanging onto human half existence group watches world rejuvenate final fantasy vi entered development release predecessor final fantasy v december 1992 development game took one year complete series creator director hironobu sakaguchi could intimately involved previous installments due projects promotion executive vice president company 1991 reason became producer split director responsibilities final fantasy vi yoshinori kitase hiroyuki ito kitase charge event production scenario ito handled battle aspects sakaguchi supervised kitase cutscene direction ensured project would coalesce whole idea behind story final fantasy vi every character protagonist members development team contributed ideas characters episodes overall plot kitase described hybrid process consequently terra locke conceived sakaguchi celes gau kitase shadow setzer graphic director tetsuya nomura edgar sabin field graphic designer kaori tanaka kitase task unite story premise provided sakaguchi individual ideas character episodes create cohesive narrative scenario final fantasy vi written group four five people among kitase provided key elements story opera scene celes suicide attempt well kefka appearances regular series character designer yoshitaka amano concept art became basis models full motion videos produced game playstation re-release tetsuya takahashi one graphic directors drew imperial magitek armors seen opening scene disregarded sakaguchi intention reuse regular designs elsewhere game sprite art characters in-game appearance drawn kazuko shibuya earlier installments sprites less detailed map battle final fantasy vi equally high resolution regardless screen enabled use animations depicting variety movements facial expressions though first game utilize super nes mode 7 graphics final fantasy vi made extensive use predecessors instance unlike final fantasy iv final fantasy v world map rendered mode 7 lends somewhat three-dimensional perspective otherwise two-dimensional game original north american localization release final fantasy vi square super nes featured several changes original japanese version obvious change game title final fantasy vi final fantasy iii two games series localized north america time final fantasy vi distributed final fantasy iii maintain naming continuity unlike final fantasy iv first released north america final fantasy ii major changes gameplay though several changes contents editorial adjustments exist english script january 1995 interview super play magazine translator ted woolsey explained certain level playfulness ... sexuality japanese games n't exist usa basically nintendo america rules guidelines consequently objectionable graphics e.g nudity censored building signs towns changed bar changed café well religious allusions e.g spell holy renamed pearl also direct allusions death killing actions violent expressions well offensive words replaced softer expressions example edgar locke terra flee chocobos figaro castle kefka orders two magitek armored soldiers chase shouting go kill japanese version translated go get also imperial troopers burn figaro castle edgar claims terra hidden inside castle kefka replies burn death japanese version replaced english version welcome barbecue similarly magitek soldiers watch edgar guests escape chocobos kefka swears japanese translated ted woolsey son submariner localization also featured changes several names tina changed terra finally dialogue text files shortened due limited data storage space available game cartridge read-only memory result additional changes rendered dialogue order compress available space playstation re-release featured minor changes english localization title game reverted final fantasy vi final fantasy iii unify numbering scheme series north america japan earlier release final fantasy vii item character names adjusted expansion fenix phoenix unlike playstation re-release final fantasy iv included later final fantasy chronicles compilation script left essentially unchanged game boy advance re-release featured new translation different translator tom slattery translation preserved character names location names terminology woolsey translation changed item spell names match conventions used recent titles series revised script preserved certain quirky lines original changing editing others cleared certain points confusion original translation wii virtual console release used final fantasy iii name snes game soundtrack final fantasy vi composed long-time series contributor nobuo uematsu score consists themes major character location well music standard battles fights boss enemies special cutscenes extensive use leitmotif one defining points audio tracks aria di mezzo carattere one latter tracks played cutscene involving opera performance track features unintelligible synthesized voice harmonizes melody technical limitations spc700 sound format chip prevented use actual vocal track although developers eventually figured overcome limitation years later orchestral album final fantasy vi grand finale features arranged version aria using italian lyrics performed svetla krasteva orchestral accompaniment version also found ending full motion video game sony playstation re-release lyrics different musical arrangement addition album orchestral game concert 4 includes extended version opera arranged conducted kōsuke onozaki performed tokyo symphony orchestra featuring wakako aokimi tetsuya ōno hiroshi kuroda vocals also performed friends concert gibson amphitheatre 2005 using new english translation lyrics album available dancing mad accompanying game final battle kefka 17 minutes long contains organ cadenza variations kefka theme ending theme combines every playable character theme one composition lasting 21 minutes original score released three compact discs japan final fantasy vi original sound version version album later released north america final fantasy iii kefka domain version album japanese counterpart except different packaging small differences translation track names album newer releases additionally final fantasy vi grand finale features eleven tracks game arranged shirō sagisu tsuneyoshi saito performed ensemble archi della scala orchestra sinfonica di milano milan symphony orchestra second arranged album features thirteen tracks game performed piano reiko nomura recently dancing mad final boss theme final fantasy vi performed play video game symphony stockholm sweden june 2 2007 group machinae supremacy nobuo uematsu former rock band black mages released progressive metal version dancing mad eponymous first album 2003 third album subtitled named premiere track rock opera version entire opera ffvi including aria di mezzo carattere performed etsuyo ota 2012 kickstarter campaign overclocked remix funded 153,633 creation multiple cd album remixes music final fantasy vi andrew aversa directed creation album balance ruin contains 74 tracks 74 artists unique style album free available overclocked remix website final fantasy vi ported sony playstation tose re-released square japan north america 1999 japan available part final fantasy collection north america available part final fantasy anthology europe sold fifty thousand limited-edition copies japanese version also released japan included final fantasy -themed alarm clock final fantasy vi playstation re-release similar original japanese release seen super famicom exception addition two full motion video opening ending sequences new screen-transition effects used start end battles graphics music sound left unchanged original version notable changes gameplay addition loading times present cartridge versions involve correction software bugs original addition new memo save feature allowing players quickly save progress playstation ram re-release included special features bestiary artwork gallery december 18 2012 port re-released part final fantasy 25th anniversary ultimate box japanese package final fantasy vi released psone classic japan april 20 2011 pal territories june 2 2011 released north america december 6 2011 final fantasy vi ported second time tose re-released final fantasy vi advance square enix japan november 30 2006 nintendo north america february 5 2007 europe july 6 2007 game boy advance last game boy advance game released asia includes additional gameplay features slightly better visuals new translation follows japanese naming conventions spells monsters however full-motion videos playstation version game four new espers re-release leviathan gilgamesh cactuar diabolos two new areas include dragons den dungeon includes kaiser dragon monster coded included original soul shrine place player fight monsters continuously three new spells also appear several bugs original fixed addition similarly handheld final fantasy re-releases bestiary music player included even japanese version music player english uses american names e.g strago stragus package features new artwork series veteran original character image designer yoshitaka amano original super famicom version released wii virtual console japan march 15 2011 pal territories europe australia march 18 2011 north america june 30 2011 game released west original north american title final fantasy iii super famicom version later released wii u virtual console japan december 22 2015 square enix released game boy advance version wii u virtual console japan nintendo re-released final fantasy vi worldwide september 2017 part company super nes/super famicom classic edition ports final fantasy vi android ios mobile operating systems announced 2013 mobile-optimized versions game released android january 15 2014 ios february 6 2014 mobile-adapted controls save features redrawn slightly blurry graphics windows pc port port android version released windows pc via steam december 16 2015 steam release featured controls optimized pc steam achievements trading cards final fantasy vi received critical acclaim commercially successful japan upon release mid-1994 square publicity department reported game sold 2.55 million copies japan united states went sale last quarter 1994 became year eighth best-selling snes cartridge despite commercial success region according sakaguchi march 31 2003 game shipped 3.48 million copies worldwide 2.62 million copies shipped japan 860,000 abroad final fantasy collection sold 400,000 copies 1999 making 31st-best-selling release year japan final fantasy anthology sold approximately 364,000 copies north america final fantasy vi advance sold 223,000 copies japan end 2006 one month release gamepro rated 5 5 stating characters plotlines multiple-choice scenarios combine form one fantastic game four reviewers electronic gaming monthly granted unanimous score 9 10 game month award commenting set new standard excellence rpgs particularly praised graphics music strong emotional involvement story several awards electronic gaming monthly 1994 video game awards including best role-playing game best japanese role-playing game best music cartridge-based game additionally later ranked game ninth 1997 list 100 greatest console games time famitsu scored 37 40 making one two highest-rated games 1994 along ridge racer part nintendo power declared game rpg hit decade noting improved sound graphics predecessors game broadened thematic scope moreover suggested much story variation play ... fans may become lost world months time nintendo power also opined game plot particularly inventive story often sappy–not written american audience 1997 nintendo power ranked eighth greatest nintendo game saying everything could want—heroes world-shattering events magic mindless evil—plus interceptor wonder dog 1996 next generation said scene terra cares village orphaned children perhaps safely named series finest hour ... game series tackled big issues reached level emotional depth complexity 2010 nintendo power listed ending final fantasy vi one best finales citing great character moments cement memorable final fantasy protagonists ever also listed opera scene demonstration touching emotional role-playing games release playstation version gamepro electronic gaming monthly rated 4 5 9.5 10 respectively final fantasy collection received 54 60 points weekly famitsu scored panel six reviewers 1999 ign described graphics playstation re-release beautiful stunning reflecting time release final fantasy iii ... represented everything rpg inspiring statistic growth systems would later influence titles like wild arms suikoden moreover praised gameplay storyline claiming aspects took ... preceding rpg concepts either came something completely new refined enough make creating atmosphere players wo n't find difficult get past simplistic graphics seemingly out-dated gameplay conventions become involved rpgamer gave perfect rating original game playstation re-release citing gameplay self-explanatory enough player could pick game customize characters equipment praising music 16-bit masterpiece alternatively describe game sound effects limited game lacking replay value due one ending one fundamental path plot ... mandatory sidequests additionally regarded game english translation unremarkable better worse others offered similar comments gameplay difficulty however referred game storyline unique aspect citing large cast characters nearly receive great deal development surprisingly large number real world issues vast majority addressed rpg since ranging teen pregnancy suicide overall rpgamer regarded game epic masterpiece truly one greatest games ever created game release game boy advance also garnered praise 2007 game boy advance re-release named eighth best game boy advance game time ign feature reflecting game boy advance long lifespan final fantasy vi often regarded one best titles series one best role-playing video games ever created 2005 ign placed final fantasy vi 56th list 100 greatest games second highest ranked final fantasy title list final fantasy iv 2006 nintendo power ranked 13th top 200 game nintendo platform suggesting might best final fantasy ever year readers japanese magazine famitsu voted 25th best game time 2008 final fantasy vi took 1 spot g4 tv top must rpgs list year screwattack named final fantasy vi third best snes game beaten super metroid 2009 final fantasy vi inducted ign videogame hall fame becoming second final fantasy game final fantasy original final fantasy 2012 also ign put final fantasy vi number one list top role-playing video games stating many moments final fantasy vi worthy celebration name biggs wedge leading terra snow poisoning doma sandy boots destruction world tragic opera ultros hold close hearts even including espers poignant character themes series date cheers final fantasy vi may name follow us tumble towards future art entertainment narrative everything keeps us gaming updated version top 100 list 2007 ign ranked final fantasy vi ninth top game time final fantasy games series continued cite game character development especially noted kefka one memorable bad guys rpg history 2009 game informer put snes version final fantasy iii eighth list top games time opining perfected 2d role-playing game fell seventh-place ranking staff gave 2001 2012 staff gamesradar ranked ninth best snes game stating remain effective moving long 1994 release means true work art demands sit high atop list regardless platform already name 14th best game time 2017 staff ign ranked second best rpg game time stating willingness explore heavy themes unthinkable outcomes — made poignant set dramatic set pieces soaring score — one biggest reasons squaresoft ’ 1994 magnum opus special final fantasy vi interactive cg game also known final fantasy sgi demo final fantasy x related actual 10th game final fantasy series final fantasy x short game demo produced square using characters settings final fantasy vi produced using new silicon graphics inc. sgi onyx workstations acquired square demo square first foray 3d graphics many assumed precursor new final fantasy title nintendo 64 video game console also used sgi hardware square however yet committed nintendo console time demo production much technology demonstrated demo later put use rendering fmv sequences final fantasy vii subsequent games playstation demo featured terra branford locke cole shadow series battles game controlled largely mouse gestures example moving cursor shape star would summon dragon attack april 27 2010 square enix producer shinji hashimoto stated development remake final fantasy vi nintendo ds undecided due technical issues later however square discussed remaking vi well v nintendo 3ds 2015 tetsuya nomura director final fantasy vii remake expressed interest remaking final fantasy v vi final fantasy vi included super nes classic edition listed final fantasy iii north american european release september 29 2017
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Computer architecture
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joe blade joe blade title series budget-price platform games written colin swinbourne published players three titles flick-screen adventures player controls title character number rooms dispatching enemies rescuing innocent people manner varies three games first joe blade title portrayed blade lone commando sent evil mastermind complex release number diplomats one earliest video games placed index germany due accusations glorified war villains resembled ss troopers game still legally obtainable effectively banned game distribution technologies internet available time german publications permitted advertise titles joe blade 2 took rather different approach first game instead soldier blade time vigilante taking city rid streets criminals rescuing old-age pensioners along way blade longer armed gun jump villains touching feet dispatch almost surreal take game stark contrast comparatively gritty realism first installment game also known considerably easier first title almost point many players managed complete game one hour-long sitting spectrum version game featured version invade-a-load featuring pac man joe blade 3 returned first title formula arming blade machine gun exclusively released zx spectrum amstrad cpc included commodore 64 instructions inlay commodore 64 version ever released 1991 players game prison riot plays similarly joe blade titles hacked version identifies joe blade 4 distributed internet
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Computer architecture
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er/studio er/studio data architecture database design software developed embarcadero technologies er/studio compatible multiple database platforms used data architects data modelers database administrators business analysts create manage database designs document reuse data assets 2015 embarcaero technologies acquired database infrastructure management software company idera inc since acquisition idera inc. er/studio renamed er/studio data architect updated features
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Databases
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mimic mimic known capitalized form former simulation computer language developed 1964 h. e. petersen f. j. sansom l. m. warshawsky systems engineering group within air force materiel command wright-patterson afb dayton ohio united states expression-oriented continuous block simulation language capable incorporating blocks fortran-like algebra mimic development midas modified integration digital analog simulator represented analog computer design written completely fortran one routine compass ran control data supercomputers mimic capable solving much larger simulation models mimic ordinary differential equations describing mathematical models several scientific disciplines engineering physics chemistry biology economics well social sciences easily solved numerical integration results analysis listed drawn diagrams also enables analysis nonlinear dynamic conditions mimic software package written fortran overlay programs executes input statements mathematical model six consecutive passes simulation programs written mimic compiled rather interpreted core simulation package variable step numerical integrator fourth-order runge-kutta method many useful functions related electrical circuit elements exist besides mathematical functions found scientific programming languages need sort statements order dependencies variables since mimic internally parts software organized overlays consider predator-prey model field marine biology determine dynamics fish shark populations simple model choose lotka–volterra equation constants given tutorial wlth initial conditions problem constants given
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Programming language topics
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arm7 arm7 group older 32-bit risc arm processor cores licensed arm holdings microcontroller use arm7 core family consists arm700 arm710 arm7di arm710a arm720t arm740t arm710t arm7tdmi arm7tdmi-s arm7ej-s arm7tdmi arm7tdmi-s popular cores family since arm7 cores released 1993 2001 longer recommended new ic designs instead arm cortex-m arm cortex-r cores preferred generation introduced thumb 16-bit instruction set providing improved code density compared previous designs widely used arm7 designs implement armv4t architecture implement armv3 armv5tej arm7tdmi 37 registers 31 gpr 6 spr designs use von neumann architecture thus versions containing cache separate data instruction caches arm7 cores obsolete one historically significant model arm7di notable introduced jtag based on-chip debugging preceding arm6 cores support represented jtag tap debugging denoted icebreaker debug module supporting hardware breakpoints watchpoints letting system stalled debugging subsequent cores included enhanced support versatile processor designed mobile devices low power electronics processor architecture capable 130 mips typical 0.13 µm process arm7tdmi processor core implements arm architecture v4t processor supports 32-bit 16-bit instructions via arm thumb instruction sets arm licenses processor various semiconductor companies design full chips based arm processor architecture arm holdings neither manufactures sells cpu devices based designs rather licenses processor architecture interested parties arm offers variety licensing terms varying cost deliverables licensees arm provides integratable hardware description arm core well complete software development toolset right sell manufactured silicon containing arm cpu integrated device manufacturers idm receive arm processor ip synthesizable rtl written verilog form ability perform architectural level optimizations extensions allows manufacturer achieve custom design goals higher clock speed low power consumption instruction set extensions optimizations size debug support etc determine components included particular arm cpu chip consult manufacturer datasheet related documentation original arm7 based earlier arm6 design used armv3 instruction set arm710 variant used cpu module acorn risc pc first arm based system chip designs arm7100 arm7500 used core arm7tdmi arm7 16 bit thumb jtag debug fast multiplier enhanced ice processor implements armv4 instruction set licensed manufacture array semiconductor companies 2009 one widely used arm cores found numerous deeply embedded system designs texas instruments licensed arm7tdmi designed nokia 6110 arm7tdmi-s variant synthesizable core arm7ej-s arm7 enhanced jazelle synthesizable version arm7 implementing armv5te instruction set originally introduced powerful arm9e core
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Computer architecture
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apple color emoji apple color emoji color typeface used apple platforms ios macos display emoji characters inclusion emoji iphone unicode standard credited promoting spreading use emoji outside japan many apple icons past present feature design based deep saturated colors gradual transitions color often incorporating subtle gloss effects first version apple color emoji released alongside iphone os 2.2 november 2008 contained 471 individual emoji glyphs originally limited japanese iphone models restriction later lifted designers first apple color emoji typeface raymond sepulveda angela guzman ollie wagner due iphone originally launching japan softbank network apple emoji designs may created resemble softbank phones example 💃 defined unicode 'dancer specified gender feminine apple softbank phones previously masculine gender-neutral others years 2011—2018 apple color emoji font expanded 471 2,776 emoji october 2018 updated emoji keyboard released ios version 8.3 update also added varied skin tones same-gender couples included unicode 6 result human emoji faces switched neutral yellow skin tone default similar smiley emoji majority apple color emoji designs updated release ios 10.2 december 2016 many appearing 3d-rendered according apple vice president user interface design alan dye emoji redesigns due advent animoji memoji higher resolution screens 157 new emoji added ios october 2018 designers apple color emoji typeface versions initial release publicly credited following apple standard practice crediting work individuals former apple employees offered accounts created various designs prior ios 5 softbank encoding used encoding emoji apple devices beginning ios 5 emoji encoded using unicode standard emoji glyphs stored png images several resolutions strikes 20 32 40 48 64 96 160 pixels squared using proprietary sbix table later standardized opentype version 1.8 font contains number easter eggs several glyphs contain portions text apple think different advertisement crazy ones ... including 1f4cb clipboard 📋 1f4c4 page facing 📄 1f4d1 bookmark tabs 📑 1f4d6 open book 📖 among others emoji specified generic objects appear apple products example 1f4bb personal computer 💻 appears modern macbook 231a wristwatch ⌚ shows apple watch 1f301 foggy 🌁 shows golden gate bridge behind san francisco fog reference apple california headquarters 1f4f0 newspaper 📰 headline reads apple times variety styles used original sets example 🐬 🐙 dolphin octopus quite stylized 'button eyes 🐈 🐀 cat rat realistic resembling watercolor paintings mixture styles creates range possible designs example 🐏 🐑 ram sheep look clearly different 🐫 🐪 bactrian camel dromedary calendar emoji 📅 showing july 17 date chosen annual world emoji day date originally referred day apple premiered ical calendar application 2002 although primarily intended onscreen display ios limited printing capabilities printed displays signs used apple color emoji designs new york magazine used apple color emoji printed feature growing use emoji
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Operating systems
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chuck chuck concurrent strongly timed audio programming language real-time synthesis composition performance runs linux mac os x microsoft windows ios designed favor readability flexibility programmer considerations raw performance natively supports deterministic concurrency multiple simultaneous dynamic control rates another key feature ability live code adding removing modifying code fly program running without stopping restarting highly precise timing/concurrency model allowing arbitrarily fine granularity offers composers researchers powerful flexible programming tool building experimenting complex audio synthesis programs real-time interactive control chuck created chiefly designed ge wang graduate student working perry r. cook chuck distributed freely terms gnu general public license mac os x linux microsoft windows iphone ipad chip chuck iphone distributed limited closed source license currently licensed public however core team stated would like explore ways open chip creating beneficial environment everyone chuck programming language loosely c-like object-oriented language strong static typing chuck distinguished following characteristics chuck standard libraries provide following simple chuck program generates sound music chuck used performances princeton laptop orchestra plork developing smule applications including ocarina emulator plork organizers attribute uniqueness performances live coding perform chuck
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Programming language topics
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microcode microcode computer hardware technique interposes layer organisation cpu hardware programmer-visible instruction set architecture computer microcode layer hardware-level instructions implement higher-level machine code instructions internal state machine sequencing many digital processing elements microcode used general-purpose central processing units although current desktop cpus fallback path cases faster hardwired control unit handle microcode typically resides special high-speed memory translates machine instructions state machine data input sequences detailed circuit-level operations separates machine instructions underlying electronics instructions designed altered freely also facilitates building complex multi-step instructions reducing complexity computer circuits writing microcode often called microprogramming microcode particular processor implementation sometimes called microprogram extensive microcoding allows small simple microarchitectures emulate powerful architectures wider word length execution units relatively simple way achieve software compatibility different products processor family hardware vendors especially ibm use term microcode synonym firmware way code within device termed microcode regardless microcode machine code example hard disk drives said microcode updated though typically contain microcode firmware lowest layer computer software stack traditionally raw binary machine code instructions processor microcode sits one level avoid confusion microprogram-related element differentiated micro prefix microinstruction microassembler microprogrammer microarchitecture etc engineers normally write microcode design phase processor storing read-only memory rom programmable logic array pla structure combination however machines also exist microcode stored sram flash memory traditionally denoted writeable control store context computers either read-only read-write memory latter case cpu initialization process loads microcode control store another storage medium possibility altering microcode correct bugs instruction set implement new machine instructions complex digital processors may also employ one possibly microcode-based control unit order delegate sub-tasks must performed essentially asynchronously parallel high-level programmer even assembly programmer normally see change microcode unlike machine code often retains backward compatibility among different processors family microcode runs exact electronic circuitry designed constitutes inherent part particular processor design microprograms consist series microinstructions control cpu fundamental level hardware circuitry example single typical horizontal microinstruction might specify following operations simultaneously control processor features one cycle microinstruction often wider 50 bits e.g. 128 bits 360/85 emulator feature microprograms carefully designed optimized fastest possible execution slow microprogram would result slow machine instruction degraded performance related application programs use instructions microcode originally developed simpler method developing control logic computer initially cpu instruction sets hardwired step needed fetch decode execute machine instructions including operand address calculations reads writes controlled directly combinational logic rather minimal sequential state machine circuitry efficient need powerful instruction sets multi-step addressing complex operations see made hard-wired processors difficult design debug highly encoded varied-length instructions contribute well especially irregular encodings used microcode simplified job allowing much processor behaviour programming model defined via microprogram routines rather dedicated circuitry even late design process microcode could easily changed whereas hard-wired cpu designs cumbersome change thus greatly facilitated cpu design 1940s late 1970s large portion programming done assembly language higher-level instructions mean greater programmer productivity important advantage microcode relative ease powerful machine instructions defined ultimate extension directly executable high level language designs statement high-level language pl/i entirely directly executed microcode without compilation ibm future systems project data general fountainhead processor examples 1970s cpu speeds grew quickly memory speeds numerous techniques memory block transfer memory pre-fetch multi-level caches used alleviate high-level machine instructions made possible microcode helped fewer complex machine instructions require less memory bandwidth example operation character string done single machine instruction thus avoiding multiple instruction fetches architectures instruction sets implemented complex microprograms included ibm system/360 digital equipment corporation vax approach increasingly complex microcode-implemented instruction sets later called cisc alternate approach used many microprocessors use plas roms instead combinational logic mainly instruction decoding let simple state machine without much microcode sequencing mos technology 6502 example microprocessor using pla instruction decode sequencing pla visible photomicrographs chip operation seen transistor-level simulation microprogramming still used modern cpu designs cases microcode debugged simulation logic functions substituted control store logic functions often faster less expensive equivalent microprogram memory processor microprograms operate primitive totally different much hardware-oriented architecture assembly instructions visible normal programmers coordination hardware microcode implements programmer-visible architecture underlying hardware need fixed relationship visible architecture makes easier implement given instruction set architecture wide variety underlying hardware micro-architectures ibm system/360 32-bit architecture 16 general-purpose registers system/360 implementations actually use hardware implemented much simpler underlying microarchitecture example system/360 model 30 8-bit data paths arithmetic logic unit alu main memory implemented general-purpose registers special unit higher-speed core memory system/360 model 40 8-bit data paths alu 16-bit data paths main memory also implemented general-purpose registers special unit higher-speed core memory model 50 full 32-bit data paths implements general-purpose registers special unit higher-speed core memory model 65 model 195 larger data paths implement general-purpose registers faster transistor circuits way microprogramming enabled ibm design many system/360 models substantially different hardware spanning wide range cost performance making architecturally compatible dramatically reduces number unique system software programs must written model similar approach used digital equipment corporation dec vax family computers result different vax processors use different microarchitectures yet programmer-visible architecture change microprogramming also reduces cost field changes correct defects bugs processor bug often fixed replacing portion microprogram rather changes made hardware logic wiring 1947 design mit whirlwind introduced concept control store way simplify computer design move beyond ad hoc methods control store diode matrix two-dimensional lattice one dimension accepts control time pulses cpu internal clock connects control signals gates circuits pulse distributor takes pulses generated cpu clock breaks eight separate time pulses activates different row lattice row activated activates control signals connected described another way signals transmitted control store played much like player piano roll controlled sequence wide words constructed bits played sequentially control store however song short repeated continuously 1951 maurice wilkes enhanced concept adding conditional execution concept akin conditional computer software initial implementation consisted pair matrices first one generated signals manner whirlwind control store second matrix selected row signals microprogram instruction word speak invoke next cycle conditionals implemented providing way single line control store could choose alternatives second matrix made control signals conditional detected internal signal wilkes coined term microprogramming describe feature distinguish simple control store microinstruction microprogram provides bits control functional elements internally compose cpu advantage hard-wired cpu internal cpu control becomes specialized form computer program microcode thus transforms complex electronic design challenge control cpu less complex programming challenge take advantage cpu divided several parts may also memory address register memory data register used access main computer storage together elements form execution unit modern cpus several execution units even simple computers usually one unit read write memory another execute user code elements could often brought together single chip chip comes fixed width would form slice execution unit known bit slice chips amd am2900 family one best known examples bit slice elements parts execution units execution units interconnected bundle wires called bus programmers develop microprograms using basic software tools microassembler allows programmer define table bits symbolically close relationship underlying architecture microcode several properties make difficult generate using compiler simulator program intended execute bits way electronics allows much freedom debug microprogram microprogram finalized extensively tested sometimes used input computer program constructs logic produce data program similar used optimize programmable logic array even without fully optimal logic heuristically optimized logic vastly reduce number transistors number required rom control store reduces cost producing electricity consumed cpu microcode characterized horizontal vertical referring primarily whether microinstruction controls cpu elements little decoding horizontal microcode requires extensive decoding combinatorial logic vertical microcode consequently horizontal microinstruction wider contains bits occupies storage space vertical microinstruction horizontal microcode several discrete micro-operations combined single microinstruction simultaneous operation horizontal microcode typically contained fairly wide control store uncommon word 108 bits tick sequencer clock microcode word read decoded used control functional elements make cpu typical implementation horizontal microprogram word comprises fairly tightly defined groups bits example one simple arrangement might type micromachine implement jump instruction address following opcode microcode might require two clock ticks engineer designing would write microassembler source code looking something like tick common find portions cpu used remaining groups bits microinstruction no-ops careful design hardware microcode property exploited parallelise operations use different areas cpu example case alu required first tick could potentially used complete earlier arithmetic instruction vertical microcode microinstruction significantly encoded bit fields generally pass intermediate combinatory logic turn generates actual control sequencing signals internal cpu elements alu registers etc. contrast horizontal microcode bit fields either directly produce control sequencing signals minimally encoded consequently vertical microcode requires smaller instruction lengths less storage requires time decode resulting slower cpu clock vertical microcode assembly language simple conventional computer emulating complex computer processors dec alpha processors cmos microprocessors later ibm system/390 mainframes z/architecture mainframes palcode term used alpha processors millicode term used ibm mainframe microprocessors form machine code access special registers hardware resources available regular machine code used implement instructions functions page table walks alpha processors another form vertical microcode two fields field select selects part cpu controlled word control store field value actually controls part cpu type microcode designer explicitly chooses make slower cpu save money reducing unused bits control store however reduced complexity may increase cpu clock frequency lessens effect increased number cycles per instruction transistors became cheaper horizontal microcode came dominate design cpus using microcode vertical microcode used less often vertical horizontal microcode used horizontal microcode may referred nanocode picocode computers built using writable microcode design rather storing microcode rom hard-wired logic microcode stored ram called writable control store wcs computer sometimes called writable instruction set computer wisc many experimental prototype computers use writable control stores also commercial machines use writable microcode burroughs small systems early xerox workstations dec vax 8800 nautilus family symbolics l- g-machines number ibm system/360 system/370 implementations dec pdp-10 machines data general eclipse mv/8000 many machines offer user-programmable writable control stores option including hp 2100 dec pdp-11/60 varian data machines v-70 series minicomputers ibm system/370 includes facility called initial-microprogram load iml impl invoked console part power-on reset por another processor tightly coupled multiprocessor complex commercial machines example ibm 360/85 read-only storage writable control store microcode wcs offers several advantages including ease patching microprogram certain hardware generations faster access roms provide user-programmable wcs allows user optimize machine specific purposes starting pentium pro 1995 several x86 cpus writable intel microcode example allowed bugs intel core 2 intel xeon microcodes fixed patching microprograms rather requiring entire chips replaced second prominent example set microcode patches intel offered processor architectures 10 years age bid counter security vulnerabilities discovered designs spectre meltdown went public start 2018 microcode update installed linux freebsd microsoft windows motherboard bios design trend toward heavily microcoded processors complex instructions began early 1960s continued roughly mid-1980s point risc design philosophy started becoming prominent cpu uses microcode generally takes several clock cycles execute single instruction one clock cycle step microprogram instruction cisc processors include instructions take long time execute variations interfere interrupt latency far important modern systems pipelining designing new processor hardwired control risc following advantages microcoded cisc counterpoints well many risc vliw processors designed execute every instruction long cache single cycle similar way cpus microcode execute one microinstruction per cycle vliw processors instructions behave similarly wide horizontal microcode although typically without fine-grained control hardware provided microcode risc instructions sometimes similar narrow vertical microcode microcoding popular application-specific processors network processors microcontrollers digital signal processors channel controllers disk controllers network interface controllers graphics processing units hardware modern cisc implementations x86 family decode instructions dynamically buffered micro-operations μops instruction encoding similar risc traditional microcode hardwired instruction decode unit directly emits μops common x86 instructions falls back traditional microcode rom complex rarely used instructions example x86 might look μops microcode handle complex multistep operations loop string instructions floating point unit transcendental functions unusual values denormal numbers special purpose instructions cpuid
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Computer architecture
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kill chain term kill chain originally used military concept related structure attack consisting target identification force dispatch target decision order attack target finally destruction target conversely idea breaking opponent kill chain method defense preemptive action recently lockheed martin adapted concept information security using method modeling intrusions computer network cyber kill chain model seen adoption information security community however acceptance universal critics pointing believe fundamental flaws model one military kill chain model f2t2ea includes following phases integrated end-to-end process described chain interruption stage interrupt entire process four fs military term used united states military especially world war ii designed easy remember four fs follows new american military contingency plan called kill chain reportedly first step new strategy use satellite imagery identify north korean launch sites nuclear facilities manufacturing capability destroy pre-emptively conflict seems imminent plan mentioned joint statement united states south korea computer scientists lockheed-martin corporation described new intrusion kill chain framework model defend computer networks 2011 wrote attacks may occur phases disrupted controls established phase since cyber kill chain™ adopted data security organizations define phases cyber-attacks cyber kill chain reveals phases cyber attack early reconnaissance goal data exfiltration kill chain also used management tool help continuously improve network defense according lockheed martin threats must progress several phases model including defensive courses action taken phases u.s. senate investigation 2013 target corporation data breach included analysis based lockheed-martin kill chain framework identified several stages controls prevent detect progression attack among critiques lockheed martin cyber kill chain model threat assessment prevention tool first phases happen outside defended network making difficult identify defend actions phases similarly methodology said reinforce traditional perimeter-based malware-prevention based defensive strategies others noted traditional cyber kill chain n't suitable model insider threat particularly troublesome given likelihood successful attacks breach internal network perimeter organizations need develop strategy dealing attackers inside firewall need think every attacker potential insider ” unified version kill chain developed overcome common critiques traditional cyber kill chain uniting extending lockheed martin ’ kill chain mitre ’ att ck framework unified kill chain ordered arrangement 18 unique attack phases may occur end-to-end cyber attacks covers activities occur outside within defended network unified kill chain improves scope limitations traditional kill chain time-agnostic nature tactics mitre ’ att ck unified model used analyze compare defend end-to-end cyber attacks advanced persistent threats apts
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Computer security
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multitier architecture software engineering multitier architecture often referred n -tier architecture multilayered architecture client–server architecture presentation application processing data management functions physically separated widespread use multitier architecture three-tier architecture n -tier application architecture provides model developers create flexible reusable applications segregating application tiers developers acquire option modifying adding specific layer instead reworking entire application three-tier architecture typically composed presentation tier domain logic tier data storage tier concepts layer tier often used interchangeably one fairly common point view indeed difference view holds layer logical structuring mechanism elements make software solution tier physical structuring mechanism system infrastructure example three-layer solution could easily deployed single tier personal workstation layers architectural pattern described various publications logical multilayered architecture information system object-oriented design following four common book domain driven design describes common uses four layers although primary focus domain layer application architecture explicit distinction business layer presentation layer i.e. presentation layer considered part business layer traditional client-server two-tier model implemented usual convention application layer service layer considered sublayer business layer typically encapsulating api definition surfacing supported business functionality application/business layers fact subdivided emphasize additional sublayers distinct responsibility example model–view–presenter pattern used presenter sublayer might used additional layer user interface layer business/application layer represented model sublayer also identify separate layer called business infrastructure layer bi located business layer infrastructure layer also sometimes called low-level business layer business services layer layer general used several application tiers e.g currencyconverter infrastructure layer partitioned different levels high-level low-level technical services developers often focus persistence data access capabilities infrastructure layer therefore talk persistence layer data access layer instead infrastructure layer technical services layer words kind technical services always explicitly thought part particular layer layer top another depends every layer exist without layers requires layers function another common view layers always strictly depend adjacent layer example relaxed layered system opposed strict layered system layer also depend layers three-tier architecture client-server software architecture pattern user interface presentation functional process logic business rules computer data storage data access developed maintained independent modules often separate platforms developed john j. donovan open environment corporation oec tools company founded cambridge massachusetts apart usual advantages modular software well-defined interfaces three-tier architecture intended allow three tiers upgraded replaced independently response changes requirements technology example change operating system presentation tier would affect user interface code typically user interface runs desktop pc workstation uses standard graphical user interface functional process logic may consist one separate modules running workstation application server rdbms database server mainframe contains computer data storage logic middle tier may multitiered case overall architecture called n -tier architecture web development field three-tier often used refer websites commonly electronic commerce websites built using three tiers data transfer tiers part architecture protocols involved may include one snmp corba java rmi .net remoting windows communication foundation sockets udp web services standard proprietary protocols often middleware used connect separate tiers separate tiers often necessarily run separate physical servers tier may run cluster end-to-end traceability data flows n -tier systems challenging task becomes important systems increase complexity application response measurement defines concepts apis measuring performance correlating transactions tiers generally term tiers used describe physical distribution components system separate servers computers networks processing nodes three-tier architecture three processing nodes term layers refers logical grouping components may may physically located one processing node
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Distributed computing architecture
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java 3d java 3d scene graph-based 3d application programming interface api java platform runs top either opengl direct3d version 1.6.0 runs top java opengl jogl since version 1.2 java 3d developed java community process java 3d scene graph directed acyclic graph dag compared solutions java 3d wrapper around graphics apis interface encapsulates graphics programming using true object-oriented approach scene constructed using scene graph representation objects shown scene graph structured tree containing several elements necessary display objects additionally java 3d offers extensive spatialized sound support java 3d documentation available download separately part java development kit jdk intel silicon graphics apple sun retained mode scene graph apis development 1996 since wanted make java version decided collaborate making project became java 3d development underway already 1997 public beta version released march 1998 first version released december 1998 mid-2003 summer 2004 development java 3d discontinued summer 2004 java 3d released community source project sun volunteers since continuing development january 29 2008 announced improvements java 3d would put hold produce 3d scene graph javafx javafx 3d support eventually released java 8 javafx 3d graphics functionality less come supersede java 3d since february 28 2008 entire java 3d source code released gpl version 2 license gpl linking exception since february 10 2012 java 3d uses jogl 2.0 hardware accelerated opengl rendering port initiated julien gouesse java 3d high-level api option render 3d java part due pause development 2003 2004 several competing java scene graph technologies emerged general purpose gaming visualization addition many c c++ scene graph apis offer java support jni lower level jogl jsr 231 opengl bindings java popular alternative scene graph apis java 3d lwjgl another binding
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Programming language topics
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xml object model xom xml document object model processing xml java strives correctness simplicity
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Programming language topics
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artmotion artmotion ltd. swiss based data housing provider operates two data centers near swiss alps designed security-seeking businesses favored country political neutrality ironclad privacy laws artmotion founded 2000 mateo meier also current ceo company 2003 artmotion acquired cyberhost swiss cloud hosting services provider 2004 became ltd. company since 2011 swiss datacenter provider everyware ltd. holds 25 percent artmotion shares artmotion increased capital 2015 2013 prism leak several cloud computing companies faced criticism lack security especially based us artmotion among swiss-based cloud computing providers gained scandal mostly due country stringent data privacy laws customer base increased company revenue 45 percent month following scandal according ceo mateo meier except european countries like luxembourg switzerland personal privacy difficult service modern world switzerland member european union hence exempt pan-european agreements share data member states well united states
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Distributed computing architecture
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xmlvend xmlvend south african developed open interface standard facilitates sale prepaid electricity credit electricity utilities clients application web services facilitate trade various types devices utility prepayment vending server standard already introduced used prepaid water
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Web technology
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schema matching terms schema matching mapping often used interchangeably database process article differentiate two follows schema matching process identifying two objects semantically related scope article mapping refers transformations objects example two schemas db1.student name ssn level major marks db2.grad-student name id major grades possible matches would db1.student ≈ db2.grad-student db1.ssn db2.id etc possible transformations mappings would db1.marks db2.grades 100-90 90-80 b etc. automating two approaches one fundamental tasks data integration general possible determine fully automatically different correspondences two schemas — primarily differing often explicated documented semantics two schemas among others common challenges automating matching mapping previously classified especially relational db schemas – fairly comprehensive list heterogeneity limited relational model recognizing schematic vs semantic differences/heterogeneity heterogeneities exist schemas use different representations definitions represent information schema conflicts different expressions units precision result conflicting representations data data conflicts research schema matching seeks provide automated support process finding semantic matches two schemas process made harder due heterogeneities following levels discusses generic methodology task schema integration activities involved according authors one view integration approaches schema integration broadly classified ones exploit either schema information schema instance level information schema-level matchers consider schema information instance data available information includes usual properties schema elements name description data type relationship types part-of is-a etc constraints schema structure working element atomic elements like attributes objects structure level matching combinations elements appear together structure properties used identify matching elements two schemas language-based linguistic matchers use names text i.e. words sentences find semantically similar schema elements constraint based matchers exploit constraints often contained schemas constraints used define data types value ranges uniqueness optionality relationship types cardinalities etc constraints two input schemas matched determine similarity schema elements instance-level matchers use instance-level data gather important insight contents meaning schema elements typically used addition schema level matches order boost confidence match results information available schema level insufficient matchers level use linguistic constraint based characterization instances example using linguistic techniques might possible look dept deptname empname instances conclude deptname better match candidate dept empname constraints like zipcodes must 5 digits long format phone numbers may allow matching types instance data hybrid matchers directly combine several matching approaches determine match candidates based multiple criteria information sources techniques also employ additional information dictionaries thesauri user-provided match mismatch information reusing matching information another initiative re-use previous matching information auxiliary information future matching tasks motivation work structures substructures often repeat example schemas e-commerce domain reuse previous matches however needs careful choice possible reuse makes sense part new schema domains example salary income may considered identical payroll application tax reporting application several open ended challenges reuse deserves work sample prototypes typically implementation matching techniques classified either rule based learner based systems complementary nature different approaches instigated number applications using combination techniques depending nature domain application consideration relationship types objects identified end matching process typically set semantics overlap disjointness exclusion equivalence subsumption logical encodings relationships mean among others early attempt use description logics schema integration identifying relationships presented several state art matching tools today benchmarked ontology alignment evaluation initiative capable identifying many simple 1:1 1 n n:1 element level matches complex matches n:1 n element structure level matches objects quality schema matching commonly measure precision recall precision measures number correctly matched pairs pairs matched recall measures many actual pairs matched
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Databases
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apper apper originally named kpackagekit free open source linux front-end application packagekit package management service kde apper also one main difference compared old kpackagekit apper list applications instead listing packages makes much user-friendly allows user search install applications without added complexity dealing packages dependencies besides installation new applications also allows easy removal updates compared ubuntu software center well appstream project apper adopted distributions fedora debian opensuse 12.1
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Operating systems
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transformers g1 awakening transformers g1 awakening turn-based tactics mobile game transformers franchise developed published glu mobile originally released feature phones november 12 2008 ported ios 2010 game redrawn applestore due licence reasons transformers g1 awakening announced botcon 2008 worldwide release set fall year second transformers game glu mobile released platform game mobile phones based michael bay 2007 live-action transformers film next transformers film would released 2009 glu decided maximize licensing agreement producing game n't tied major release unlike film adaptations awakening planned turn-based tactics game role-playing elements story set early days 1980s animated series interview fan site tformers.com glu mobile emea studio head chris white awakening product manager martin edelman explained desire make game based admiration well marvel comics series compared game advance wars series explained differed units expendable cannon fodder instead unit unique character franchise individual strengths attributes based existing personas game developed glu uk office previously company macrospace previous experience turn-based tactics games developed ancient empires series like turn-based tactics games player controls units case cast 23 transformers characters across small-scale grid-based levels order encourage much transforming possible player given option turn robot vehicle form end turn vehicle mode transformers travel receive reduced damage attack robot mode gain ability attack transformers capture structures necessary produce energy like pylons energy sources provide energon acts currency game energon allows player upgrade repair units summon additional characters play main campaign players control heroic autobots battling megatron forces villainous decepticons starting game bumblebee ratchet additional characters added story progresses unique abilities characteristics autobot leader optimus prime gives moral boost friendly units adjacent spaces increases battle performance ratchet turns ambulance game medic survival key robots survival city-sized metroplex serves autobot mobile base used summon supporting characters like prowl ironhide sideswipe trypticon serves function decepticons boombox blaster able summon minicassettes eject rewind goes decepticon soundwave underlings frenzy rumble cartoon jetfire must converted decepticon transforming tyrannosaur grimlock crushes decepticons ease initial release non-smart mobile phones 2008 drew positive attention based concept alone commenting announcement september release date pocket gamer spanner spencer said glad hear game based original series live-action film latter described pile rust cleverly disguised cgi extravaganza kotaku luke plunkett impressed early trailer game hoping developers would realize value port nintendo ds later repeated sentiment announcing playable java-based demo saying game looked surprisingly fantastic reviewers actually able play game equally positive early hands-on preview pocket gamer keith andrew claimed never previously understood appeal transformers said game bursting fun though felt game objectives challenging may require several play-throughs master also felt controls simple enough newcomers would daunted commended glu mobile creating game caters fan base appeals wider audience later full review described gameplay resource management meets chess felt game made trial-and-error puzzle-like nature levels somehow enjoyable rather frustrating gave game score 8/10 awarded pocket gamer silver award 2008 mobile release awakening featured retrospective titled visual history optimus prime video games ign jack devries brian altano felt awakening addition pretty good strategy game first game perfect appearance optimus prime supplanted later felt cel-shaded graphics colorful flat textures made optimus pop screen like action figure 2010 ports smartphone operating systems met similar enthusiasm initial announcement kotaku mike fahey wrote eagerly awaited game featured g1 transformers michael bay-bots later full review kotaku luke plunkett called game surprisingly authentic regards animated series also felt game could stand well made turn-based strategy game said 3d rendered battle sequences looked glorious iphone felt downside simplistic graphics animation outside battle showed game roots mobile game concluded recommending game anyone either long-suffering fan animated transformers fan turn-based strategy games stating easily one best games genre available ios ign levi buchanan felt although lifelong affinity transformers inclined judge poorly made adaptations harshly awakening disappoint transformers fans lauded thoughtful merger advance wars -style gameplay classic transformers fiction stating game great story strength transformers expertly woven entire production felt mission goals completely inline advancing story nothing arbitrary also felt glu choice transformers characters excellent thought cel-shading dynamic camera battle sequences made robot models look terrific gave game score 8.5 10 concluded stating transformers g1 awakening quite simply best transformers game ever played
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Operating systems
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need speed undercover need speed undercover 2008 racing video game twelfth instalment need speed series developed ea black box published electronic arts released november 18 2008 playstation 2 playstation 3 xbox 360 wii microsoft windows playstation portable nintendo ds number mobile phone platforms edition game ios later released april 27 2009 game sees players conducting illegal street races within fictional tri-city area main mode story focused player operating undercover police officer investigate links criminal syndicate stolen cars street racers gameplay operates manner previous entries though included larger selection licensed real-world cars rpg-styled system game main mode upon release game received mixed reviews many criticised game difficulty setting repetitive elements editions receiving lower scores due severe issues undercover later succeeded 2009 2010 game players take part illegal street races focus different styles races utilizing variety licensed real-world cars available time game development release upgraded customized new parts contending involvement police efforts impede player racing events featured game include series standard circuit point-to-point checkpoint races alongside return police pursuit events featured wanted addition undercover includes new events outrun players must overtake rival stay ahead period time highway battle similar carbon duel event players attempt stay ahead rival highway battling local traffic winning instantly pull far ahead losing exact opposite game modes consisting career single event multiplayer playstation 2 wii editions also feature fourth mode challenge series operates similar function wanted carbon career mode players take role undercover police officer seeking break syndicate operating within underground street race world like wanted players achieve completing racing events pursuit events majority events mode include opportunity dominate completing faster specified time record domination undercover progress story involves completing events earn money also experience wheelman rep special performance bonus bonuses either improve player driving abilities cars provide bonuses player playthrough i.e increase race earnings earning enough experience levels player wheelman level unlocking larger performance bonus new cars upgrade parts well additional events including jobs special story-based missions player must complete specific task taking criminal car police pursuits mode function like previous editions though player wheelman level directly impacts aggressive police pursuit player higher level tactics vehicle types used pursuit players freely select event game map using hotkey move highlighted event completing current one able replay previous events reduced amount cash game features wide variety licensed real-world cars divided three tiers performance four classes exotic tuner muscle sport players begin career mode limited selection cars use purchase unlock level earn additional cars defeating criminals story cars upgrades customisation done visiting player safehouse rather separate stores fine-tuning car performance also conducted manner nintendo ds playstation 2 playstation portable wii editions game players also use police vehicles upon unlocking main mode cars receive cosmetic damage game except highway battles job events possible total car event latter per specific parameters assigned job player undertaking multiplayer mode varies across platforms game launched online multiplayer possible windows playstation 3 xbox 360 editions playstation 2 wii editions feature split-screen multiplayer mobile phone platforms include game mode online multiplayer events consist multiplayer versions sprint racing highway battle along team-based event entitled cops robbers two teams players compete score points across two rounds first round robbers collect flags deliver specified areas score points cops attempt arrest earn points whereupon second round teams switch roles team highest score winning match playstation 2 wii features cops robbers multiplayer mode albeit fewer players allowed also feature two exclusive events lap knockout players compete across circuit last player end lap knocked winner remaining player end timed circuit players compete across circuit predetermined length laps time player first place end winning event game story events take place fictional region tri-city bay name influenced real-life city tri-city oregon mainly daytime sunrise sunset region consists four borough palm harbor downtown city district port crescent industrial port also houses naval base gold coast mountains mountainous region observatories wind farms sunset hills suburban town rural farms borough linked series highways region design heavily influenced real-life city miami alongside locations visited development team across gulf coast california coast setting open world map consisting around road nintendo ds edition boroughs named metropolis north port crescent south port crescent riverton wii playstation 2 editions game setting takes place within carbon-copy two boroughs taken wanted setting player undercover police officer tri-city bay police department tcbpd called palm harbor police station superior lt. jack keller paul pape player informed current investigation region underground street racing world joined inspector chase linh maggie q federal agent fbi wants bring international criminal syndicate operating region involved smuggling stolen cars player instructed pose new street racer join major illegal street races along gaining infamy tcbpd order secure entry syndicate player achieves recruited gang works syndicate run hector maio kurt caceres brother zack joshua alba time befriend carmen mendenz christina milian member gang brothers quickly assign player steal cars racing activities upon completing jobs chase instructs player arrest gang including brothers hector gang action player sent sunset hills order get recruited crew operated gmac david rees snell former tcbpd police officer rose largo heather fox honor student turned crime brad nickel rogers lawrence b. adisa former boxer whilst conducting races along jobs crew player instructed gmac steal car chau wu daniel d. lee leader syndicate player investigating player finds confronted chau offers overlook theft exchange player help recovering car lost needs back believing stolen gmac crew meeting carmen suggests theft likely committed someone else eventually player instructed arrest gmac crew though unable locate stolen car possession shortly arresting gmac crew carmen contacts players requests meeting upon reaching reveals zack hector unknowingly stole missing car chau asks get rid chau quickly contacts player moment take possession receive instructions deliver warehouse learning knows police officer kidnapped chase coerce compliance upon delivering car chase reveals corrupt federal agent working chau recover car possessed vital evidence activities sizeable quantity cash chau dispose player chase betrays murdering henchman framing player murder escaping money evidence player forced flee tcbpd upon wanted killings finds support keller instructions proceed take chase flee region way clear name successfully arresting chase keller commends player hard work recovering evidence managing forget undercover work informing carmen made plea bargain exchange testimony arrested crews time later player meets carmen give ride local university studying med student electronic arts ceo john riccitiello stated previous release series prostreet okay game ... good undercover would much better game stated undercover would considerably longer development cycle predecessors need speed development team split two teams would work two-year development cycle future titles alternating releases riccitiello stated torturing development team tight development cycle past change implemented mid-summer 2007 one team started working undercover giving 16.5 month development cycle team finished prostreet would start working next title riccitiello also stated undercover took inspiration action films transporter large embedded narrative frank gibeau president ea games label stated development due fact sales prostreet n't live ea hopes game need speed franchise would go back roots although undercover already developed prostreet john doyle developer ea black box said undercover would feature brand new game mechanic -ish sandbox style gameplay game also provided new damage system andy blackmore senior vehicle concept artist ea explained one porsche cars conceptualized game brought life game brief description approved porsche days undercover release ea revealed plot details video uploaded showed player evading capture tri-city police department tcpd reception undercover mixed complaints game easy difficulty repetitiveness poor texture maintenance ign review went far recommending game rivals rockstar games ea burnout paradise ign review critical ps3 version undercover giving 4/10 calling poor game ton problems practically redeeming qualities ign also commented reason open world environment lost player could start event map however xbox 360 pc versions received higher score contrast ps3 version ign review due fewer severe problems occurred 1up.com review called game fairly successful praised games selection cars tighter handling vehicles however leveling system unlocks cars upgrades criticized resembling grinding general sparse traffic wide-open roads poor ai led complaints extremely low difficulty however one reviewer commented may marketing ploy target wider audience reception live-action cutscenes almost universally negative many critics noting videos poorly acted lacked purpose compared cutscenes michael bay roland emmerich film lack connection crime fighting undercover cop story racing game play particularly criticized ign said ... run missions steal cars make 'special deliveries things like never actually see sequences show cops putting evidence together anything sort chase linh tell need get inside racing group order get dirt race 'll say 'we enough let move 're left asking help finally in-game frame rate received little praise gamespot particularly criticized ps3 version problem resulting lower score platform compared xbox 360 pc versions need speed undercover sold 1.4 million copies united states
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Operating systems
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tinyscheme tinyscheme free software implementation scheme programming language lightweight scheme interpreter subset rrs standard meant used embedded scripting interpreter programs much functionality tinyscheme included conditionally allow developers balance features size/footprint tinyscheme used gnu image manipulation program gimp starting version 2.4 released 2007 gimp previously used siod tinyscheme used core direct revenue adware making world widely distributed scheme runtime
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Programming language topics
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hol light hol light member hol theorem prover family like members proof assistant classical higher order logic compared hol systems hol light intended relatively simple foundations hol light authored maintained mathematician computer scientist john harrison hol light released simplified bsd license hol light based formulation type theory equality primitive notion primitive rules inference following formulation type theory close one described section ii.2
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Programming language topics
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gpss general purpose simulation system gpss discrete time simulation general-purpose programming language simulation clock advances discrete steps system modelled transactions enter system passed one service represented blocks another used primarily process flow oriented simulation language particularly well-suited problems factory gpss developed ibm geoffrey gordon beginning 1960s named gordon programable simulation system name changed ibm decided release product general program part new name create standard waiting-line simulations original releases ibm 7044 7090 mainframes subsequently releases ibm 360 univac 1108 cdc time implementations languages targeted different size systems developed including dec vax specialized apl version large-scale univac systems macintosh among others gpss java general purpose simulation system java-based tool developed teach gpss simulation language gpss resembles lego structure blocks chosen modeller specific functions imitate particular system language neither procedural object-oriented functional programming world simulated entities moving model entities called transactions envisioned moving block block block line code represents unit actions affects transaction entities blocks facility-oriented machines job shop transaction-oriented parts work-in-process signals electronic components documents bureaucratic procedure gpss automatically keep track statistics brings fixed form end simulation standard report gpss one oldest language candidate first object-oriented approach transactions truly instances model objects blocks methods modern concept oop entities broadly classified resources computational entities statistical entities resources like facilities storages represent limited capacity resources computational entities like ampervariables variables functions random generators used represent state transactions elements environment statistical entities like queues tables histograms collect statistical information interest following example taken simulation using gpss hello world gpss illustrate main concepts aim simulate one day operation barber shop customers arrive random constant flow enter shop queue barber busy get hair cut first-come first-served basis leave shop wish know average maximum waiting line well number customers program comprised codice_1 codice_2 statements divided model segments control cards first segment models customers codice_3 block creates flow transactions schedules enter model inter-arrival time uniformly distributed range 18±6 programmer responsibility interpret transaction customers understand time counted minutes transactions start existence codice_3 block progress block block according certain rules reach codice_5 remove model normally transactions progress one block next one customer transactions leave codice_3 block enter codice_7 block block simulates waiting line collects statistics accordingly example materialize line chairs end simulation know among things maximum queue size many chairs needed average waiting time codice_8 block requires name queue parameter one queue may exist model one associated codice_9 block triggered transaction leaves queue gpss remembers transactions queue possible know average time spent check buggy transaction leaving queue without previously entering codice_10 block transaction try proceed codice_11 block block simulating capture facility named joe facilities model single servers capacity one facility busy codice_12 deny attempting transaction right enter example customer wait codice_8 block free soon becomes available transaction allowed capture facility mark busy others transactions start count service time statistics transaction passes corresponding codice_14 block codice_12 codice_16 pairs linked facility name many independent facilities may exist model model operators like barber repairman agent also pieces equipment like crane gas station authorization document etc. fact anything capacity one simulate multiple parallel servers like team five barbers oven capacity 10 gpss uses entities named codice_17s customer seizes joe proceeds next statement codice_18 whose task freeze entity prescribed length time random number picked 16-4=12 16+4=20mn service time distributions available gpss codice_19 somehow different notion function programming languages time transactions allowed move model blocking facilities may exist model joe facility busy frozen customer prescribed time customer wake proceed next statement free joe codice_5 next transaction previous block customer sitting chair able codice_11 select next transaction gpss uses first-come first-served basis priority selection policies programmed direct manipulation future event chain entity parallel first segment simulating customer behavior second model segment simulates end day time 480mn 8h entity codice_3d codice_5 next block time codice_5 parameter 1 meaning special counter decreased 1 counter reaches 0 program stops output printed special counter set codice_25 statement example set one thus simulation finish one run 480 mn simulated time output contains indicates joe busy 86.0 time gave hair cut 26 customers hair cut took 15.88 minutes average incidentally joe cutting hair customer number 26 simulation closed programming provisions taken barber finish hair cut closing shop indicates also maximum 1 customer observed waiting turn fact number waiting customer average 0.160 total 27 customers enter queue customer number 27 still sitting waiting turn joe closed shop 27 customers 12 served without wait fact queue empty 44.4 time average waiting time 2.851 min average waiting time 15=27-12 customers really wait 5.133 min
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Programming language topics
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microkernel computer science microkernel often abbreviated μ-kernel near-minimum amount software provide mechanisms needed implement operating system os mechanisms include low-level address space management thread management inter-process communication ipc hardware provides multiple rings cpu modes microkernel may software executing privileged level generally referred supervisor kernel mode traditional operating system functions device drivers protocol stacks file systems typically removed microkernel instead run user space terms source code size microkernels often smaller monolithic kernels minix 3 microkernel example approximately 12,000 lines code microkernels trace roots back danish computer pioneer per brinch hansen tenure danish computer company regnecentralen led software development efforts rc 4000 computer 1967 regnecentralen installing rc 4000 prototype polish fertilizer plant puławy computer used small real-time operating system tailored needs plant brinch hansen team became concerned lack generality reusability rc 4000 system feared installation would require different operating system started investigate novel general ways creating software rc 4000 1969 effort resulted completion rc 4000 multiprogramming system nucleus provided inter-process communication based message-passing 23 unprivileged processes 8 time protected one another implemented scheduling time slices programs executed parallel initiation control program execution request running programs initiation data transfers peripherals besides elementary mechanisms built-in strategy program execution resource allocation strategy implemented hierarchy running programs parent processes complete control child processes acted operating systems following brinch hansen work microkernels developed since 1970s term microkernel first appeared later 1981 microkernels meant response changes computer world several challenges adapting existing mono-kernels new systems new device drivers protocol stacks file systems low-level systems developed time code normally located monolithic kernel thus required considerable work careful code management work microkernels developed idea services would implemented user-space programs like allowing worked monolithically started stopped like program would allow services easily worked also separated kernel code allow finely tuned without worrying unintended side effects moreover would allow entirely new operating systems built common core aiding os research microkernels hot topic 1980s first usable local area networks introduced mechanisms allowed kernel distributed user space also allowed system distributed across network links first microkernels notably mach proved disappointing performance inherent advantages appeared great major line research late 1990s however time speed computers grew greatly relation networking systems disadvantages performance came overwhelm advantages development terms many attempts made adapt existing systems better performance overhead always considerable efforts required user-space programs moved back kernel 2000 large-scale mach-like efforts ended although apple macos released 2001 uses hybrid kernel called xnu combines heavily modified hybrid osfmk 7.3 kernel code bsd unix kernel also used ios tvos watchos mach-based gnu hurd also functional included testing versions arch linux debian although major work microkernels largely ended experimenters continued development since shown many performance problems earlier designs fundamental limitation concept instead due designer desire use single-purpose systems implement many services possible using pragmatic approach problem including assembly code relying processor enforce concepts normally supported software led new series microkernels dramatically improved performance microkernels closely related exokernels also much common hypervisors latter make claim minimality specialized supporting virtual machines indeed l4 microkernel frequently finds use hypervisor capacity early operating system kernels rather small partly computer memory limited capability computers grew number devices kernel control also grew throughout early history unix kernels generally small even though contained various device drivers file system implementations address spaces increased 16 32 bits kernel design longer constrained hardware architecture kernels began grow larger berkeley software distribution bsd unix began era larger kernels addition operating basic system consisting cpu disks printers bsd added complete tcp/ip networking system number virtual devices allowed existing programs work 'invisibly network growth continued many years resulting kernels millions lines source code result growth kernels prone bugs became increasingly difficult maintain microkernel intended address growth kernels difficulties resulted theory microkernel design allows easier management code due division user space services also allows increased security stability resulting reduced amount code running kernel mode example networking service crashed due buffer overflow networking service memory would corrupted leaving rest system still functional inter-process communication ipc mechanism allows separate processes communicate usually sending messages shared memory strictly speaking also inter-process communication mechanism abbreviation ipc usually refers message passing latter particularly relevant microkernels ipc allows operating system built number small programs called servers used programs system invoked via ipc support peripheral hardware handled fashion servers device drivers network protocol stacks file systems graphics etc ipc synchronous asynchronous asynchronous ipc analogous network communication sender dispatches message continues executing receiver checks polls availability message alerted via notification mechanism asynchronous ipc requires kernel maintains buffers queues messages deals buffer overflows also requires double copying messages sender kernel kernel receiver synchronous ipc first party sender receiver blocks party ready perform ipc require buffering multiple copies implicit rendezvous make programming tricky programmers prefer asynchronous send synchronous receive first-generation microkernels typically supported synchronous well asynchronous ipc suffered poor ipc performance jochen liedtke assumed design implementation ipc mechanisms underlying reason poor performance l4 microkernel pioneered methods lowered ipc costs order magnitude include ipc system call supports send well receive operation making ipc synchronous passing much data possible registers furthermore liedtke introduced concept direct process switch ipc execution incomplete context switch performed sender directly receiver l4 part message passed registers transfers in-register part message without copying furthermore overhead invoking scheduler avoided especially beneficial common case ipc used rpc-type fashion client invoking server another optimization called lazy scheduling avoids traversing scheduling queues ipc leaving threads block ipc ready queue scheduler invoked moves threads appropriate waiting queue many cases thread gets unblocked next scheduler invocation approach saves significant work similar approaches since adopted qnx minix 3 series experiments chen bershad compared memory cycles per instruction mcpi monolithic ultrix microkernel mach combined 4.3bsd unix server running user space results explained mach poorer performance higher mcpi demonstrated ipc alone responsible much system overhead suggesting optimizations focused exclusively ipc limited impact liedtke later refined chen bershad results making observation bulk difference ultrix mach mcpi caused capacity cache-misses concluding drastically reducing cache working set microkernel solve problem client-server system communication essentially synchronous even using asynchronous primitives typical operation client invoking server waiting reply also lends efficient implementation microkernels generally followed l4 lead provided synchronous ipc primitive asynchronous ipc could implemented top using helper threads however experience shown utility synchronous ipc dubious synchronous ipc forces multi-threaded design onto otherwise simple systems resulting synchronization complexities moreover rpc-like server invocation sequentializes client server avoided running separate cores versions l4 deployed commercial products therefore found necessary add asynchronous notification mechanism better support asynchronous communication signal-like mechanism carry data therefore require buffering kernel two forms ipc nonetheless violated principle minimality versions l4 switched asynchronous ipc completely synchronous ipc blocks first party ready unrestricted use could easily lead deadlocks furthermore client could easily mount denial-of-service attack server sending request never attempting receive reply therefore synchronous ipc must provide means prevent indefinite blocking many microkernels provide timeouts ipc calls limit blocking time practice choosing sensible timeout values difficult systems almost inevitably use infinite timeouts clients zero timeouts servers consequence trend towards providing arbitrary timeouts flag indicates ipc fail immediately partner ready approach effectively provides choice two timeout values zero infinity recent versions l4 minix gone path older versions l4 used timeouts qnx avoids problem requring client specify reply buffer part message send call server replies kernel copies data client buffer without wait client receive response explicitly microkernel servers essentially daemon programs like others except kernel grants privileges interact parts physical memory otherwise limits programs allows servers particularly device drivers interact directly hardware basic set servers general-purpose microkernel includes file system servers device driver servers networking servers display servers user interface device servers set servers drawn qnx provides roughly set services offered unix monolithic kernel necessary servers started system startup provide services file network device access ordinary application programs servers running environment user application server development similar ordinary application development rather build-and-boot process needed kernel development additionally many crashes corrected simply stopping restarting server however part system state lost failing server hence approach requires applications cope failure good example server responsible tcp/ip connections server restarted applications experience lost connection normal occurrence networked system services failure less expected may require changes application code qnx restart capability offered qnx high availability toolkit device drivers frequently perform direct memory access dma therefore write arbitrary locations physical memory including various kernel data structures drivers must therefore trusted common misconception means must part kernel fact driver inherently less trustworthy part kernel running device driver user space necessarily reduce damage misbehaving driver cause practice beneficial system stability presence buggy rather malicious drivers memory-access violations driver code opposed device may still caught memory-management hardware furthermore many devices dma-capable drivers made untrusted running user space recently increasing number computers feature iommus many used restrict device access physical memory also allows user-mode drivers become untrusted user-mode drivers actually predate microkernels michigan terminal system mts 1967 supported user space drivers including file system support first operating system designed capability historically drivers less problem number devices small trusted anyway kernel simplified design avoided potential performance problems led traditional driver-in-the-kernel style unix linux windows nt proliferation various kinds peripherals amount driver code escalated modern operating systems dominates kernel code size microkernel must allow building arbitrary operating system services top must provide core functionality minimum includes minimal design pioneered brinch hansen nucleus hypervisor ibm vm since formalised liedtke minimality principle concept tolerated inside microkernel moving outside kernel i.e. permitting competing implementations would prevent implementation system required functionality everything else done usermode program although device drivers implemented user programs may processor architectures require special privileges access i/o hardware related minimality principle equally important microkernel design separation mechanism policy enables construction arbitrary systems top minimal kernel policy built kernel overwritten user level therefore limits generality microkernel policy implemented user-level servers changed replacing servers letting application choose competing servers offering similar services efficiency microkernels contain schedulers manage timers violation minimality principle principle policy-mechanism separation start booting microkernel-based system requires device drivers part kernel typically means packaged kernel boot image kernel supports bootstrap protocol defines drivers located started traditional bootstrap procedure l4 microkernels microkernels simplify placing key drivers inside kernel violation minimality principle lynxos original minix examples even include file system kernel simplify booting microkernel-based system may boot via multiboot compatible boot loader systems usually load statically-linked servers make initial bootstrap mount os image continue bootstrapping key component microkernel good ipc system virtual-memory-manager design allows implementing page-fault handling swapping usermode servers safe way since services performed usermode programs efficient means communication programs essential far monolithic kernels design ipc system makes breaks microkernel effective ipc system must low overhead also interact well cpu scheduling mainstream processors obtaining service inherently expensive microkernel-based system monolithic system monolithic system service obtained single system call requires two mode switches changes processor ring cpu mode microkernel-based system service obtained sending ipc message server obtaining result another ipc message server requires context switch drivers implemented processes function call implemented procedures addition passing actual data server back may incur extra copying overhead monolithic system kernel directly access data client buffers performance therefore potential issue microkernel systems indeed experience first-generation microkernels mach chorusos showed systems based performed poorly however jochen liedtke showed mach performance problems result poor design implementation specifically mach excessive cache footprint liedtke demonstrated l4 microkernel careful design implementation especially following minimality principle ipc costs could reduced order magnitude compared mach l4 ipc performance still unbeaten across range architectures results demonstrate poor performance systems based first-generation microkernels representative second-generation kernels l4 constitutes proof microkernel-based systems built good performance shown monolithic linux server ported l4 exhibits percent overhead native linux however single-server system exhibits advantages microkernels supposed provide structuring operating system functionality separate servers number commercial multi-server systems exist particular real-time systems qnx integrity comprehensive comparison performance relative monolithic systems published multiserver systems furthermore performance seem overriding concern commercial systems instead emphasize reliably quick interrupt handling response times qnx simplicity sake robustness attempt build high-performance multiserver operating system ibm sawmill linux project however project never completed shown meantime user-level device drivers come close performance in-kernel drivers even high-throughput high-interrupt devices gigabit ethernet seems imply high-performance multi-server systems possible security benefits microkernels frequently discussed context security minimality principle microkernels argued direct consequence principle least privilege according code privileges needed provide required functionality minimality requires system trusted computing base tcb kept minimal kernel code executes privileged mode hardware unvetted access data thus violate integrity confidentiality kernel always part tcb minimizing natural security-driven design consequently microkernel designs used systems designed high-security applications including keykos eros military systems fact common criteria cc highest assurance level evaluation assurance level eal 7 explicit requirement target evaluation simple acknowledgment practical impossibility establishing true trustworthiness complex system unfortunately term simple misleading ill-defined least department defense trusted computer system evaluation criteria introduced somewhat precise verbiage b3/a1 classes recent work microkernels focusing formal specifications kernel api formal proofs api security properties implementation correctness first example mathematical proof confinement mechanisms eros based simplified model eros api recently comprehensive set machine-checked proofs performed properties protection model version l4 led referred third-generation microkernels characterised security-oriented api resource access controlled capabilities virtualization first-class concern novel approaches kernel resource management design goal suitability formal analysis besides usual goal high performance examples coyotos nova redox fiasco.oc case sel4 complete formal verification implementation achieved i.e mathematical proof kernel implementation consistent formal specification provides guarantee properties proved api actually hold real kernel degree assurance goes beyond even cc eal7 followed proofs security-enforcement properties api proof demonstrating executable binary code correct translation c implementation taking compiler tcb taken together proofs establish end-to-end proof security properties kernel term nanokernel picokernel historically referred also least one case term nanokernel used refer small kernel one supports nanosecond clock resolution
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Computer architecture
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computer terminal computer terminal electronic electromechanical hardware device used entering data displaying printing data computer computing system teletype example early day hardcopy terminal predated use computer screen decades acronym crt cathode-ray tube referred computer terminal come refer type screen personal computer early terminals inexpensive devices slow compared punched cards paper tape input technology improved video displays introduced terminals pushed older forms interaction industry related development timesharing systems evolved parallel made inefficiencies user typing ability ability support multiple users machine terminal function terminal confined display input data device significant local programmable data processing capability may called smart terminal fat client terminal depends host computer processing power called dumb terminal thin client personal computer run terminal emulator software replicates function terminal sometimes allowing concurrent use local programs access distant terminal host system terminal first working programmable fully automatic digital turing-complete computer z3 keyboard row lamps show results early user terminals connected computers electromechanical teleprinters/teletypewriters teletypewriter tty teletype model 33 asr originally used telegraphy friden flexowriter keyboard/printer terminals came later included ibm 2741 1965 decwriter la30 1970 respective top speeds teletypes ibm 2741 la30 10 15 30 characters per second although time paper king speed interaction relatively limited early video computer displays sometimes nicknamed glass ttys glass teletypes visual display units vdus used cpu instead relying individual logic gates primitive lsi chips nevertheless quickly became extremely popular input-output devices many different types computer system several suppliers gravitated set common standards datapoint 3300 computer terminal corporation announced 1967 shipped 1969 making one earliest stand-alone display-based terminals solved memory space issue mentioned using digital shift-register design using 72 columns rather later common choice 80 starting datapoint 3300 late 1970s early 1980s dozens manufacturers terminals including lear-siegler adds data general dec hazeltine corporation heath/zenith hewlett packard ibm televideo volker-craig wyse many incompatible command sequences although many used early adm-3 starting point great variations control codes makers gave rise software identified grouped terminal types system software would correctly display input forms using appropriate control codes unix-like systems termcap terminfo files stty utility term environment variable would used data general business basic software example login-time sequence codes sent terminal try read cursor position 25th line contents using sequence different manufacturer control code sequences terminal-generated response would determine single-digit number 6 data general dasher terminals 4 adm 3a/5/11/12 terminals 0 2 tty special features would available programs say set codes use great majority terminals monochrome manufacturers variously offering green white amber sometimes blue screen phosphors amber claimed reduce eye strain terminals modest color capability also available widely used example color version popular wyse wy50 wy350 offered 64 shades character cell intelligent terminal processing usually implying microprocessor built terminals microprocessors real processing input main computer attached would respond quickly keystroke term intelligent context dates 1969. notable examples include ibm 2250 ibm 2260 predecessors ibm 3270 introduced system/360 1964 terminals connected minicomputers mainframe computers often green amber screen typically terminals communicate computer via serial port via null modem cable often using eia rs-232 rs-422 rs-423 current loop serial interface ibm systems communicated coaxial cable using ibm sna protocol many dec data general ncr computers many visual display suppliers competing computer manufacturer terminals expand systems fact instruction design intel 8008 originally conceived computer terminal corporation processor datapoint 2200 introduction ibm 3270 dec vt100 1978 user programmer could notice significant advantages vdu technology improvements yet programmers used features new terminals backward compatibility vt100 later televideo terminals example dumb terminals allowed programmers continue use older software dumb terminals able respond escape sequences without needing microprocessors used multiple printed circuit boards many integrated circuits single factor classed terminal intelligent ability process user-input within terminal—not interrupting main computer keystroke—and send block data time example user finished whole field form terminals early 1980s adm-3a tvi912 data general d2 dec vt52 despite introduction ansi terminals 1978 essentially dumb terminals although later adm tvi models primitive block-send capability common early uses local processing power included features little off-loading data processing host computer added useful features printing local printer buffered serial data transmission serial handshaking accommodate higher serial transfer speeds sophisticated character attributes display well ability switch emulation modes mimic competitor models became increasingly important selling features 1980s especially buyers could mix match different suppliers equipment greater extent advance microprocessors lower memory costs made possible terminal handle editing operations inserting characters within field may previously required full screen-full characters re-sent computer possibly slow modem line around mid 1980s intelligent terminals costing less dumb terminals would years earlier could provide enough user-friendly local editing data send completed form main computer providing even processing possibilities workstations like televideo ts-800 could run cp/m-86 blurring distinction terminal personal computer another motivations development microprocessor simplify reduce electronics required terminal also made practicable load several personalities single terminal qume qvt-102 could emulate many popular terminals day sold organizations wish make software changes frequently emulated terminal types included ansi x3.64 escape code standard produced uniformity extent significant differences remained example vt100 heathkit h19 ansi mode televideo 970 data general d460 qume qvt-108 terminals followed ansi standard yet differences might exist codes function keys character attributes available block-sending fields within forms foreign character facilities handling printers connected back screen term intelligent terminal refer store check-out computer early ibm pcs single color green screens screens terminals screen pc contain character generation hardware video signals video formatting generated video display card pc graphics modes cpu software ibm pc monitor whether green monochrome display 16-color display technically much similar analog tv set without tuner terminal suitable software pc could however emulate terminal capacity could connected mainframe minicomputer data general one could booted terminal emulator mode rom eventually microprocessor-based personal computers greatly reduced market demand conventional terminals 1990s especially thin clients x terminals combined economical local processing power central shared computer facilities retain advantages terminals personal computers today pc telnet clients provide emulation common terminal dec vt100 using ansi escape code standard x3.64 could run x terminals using software cygwin/x microsoft windows x.org server software linux since advent subsequent popularization personal computer genuine hardware terminals used interface computers today using monitor keyboard modern operating systems like linux bsd derivatives feature virtual consoles mostly independent hardware used using graphical user interface gui like x window system one display typically occupied collection windows associated various applications rather single stream text associated single process case one may use terminal emulator application within windowing environment arrangement permits terminal-like interaction computer running command line interpreter example without need physical terminal device even allow running multiple terminal emulators device character-oriented terminal type computer terminal communicates host one character time opposed block-oriented terminal communicates blocks data common type data terminal easy implement program connection mainframe computer terminal server achieved via rs-232 serial links ethernet proprietary protocols text terminal often terminal sometimes text console serial computer interface text entry display information presented array pre-selected formed characters devices use video display cathode-ray tube called video display unit visual display unit vdu video display terminal vdt system console text terminal used operate computer modern computers built-in keyboard display console unix-like operating systems linux freebsd virtual consoles provide several text terminals single computer fundamental type application running text terminal command line interpreter shell prompts commands user executes command press enter includes unix shells interactive programming environments shell commands small applications another important application type text editor text editor occupies full area display displays one text documents allows user edit documents text editor many uses replaced word processor usually provides rich formatting features text editor lacks first word processors used text communicate structure document later word processors operate graphical environment provide wysiwyg simulation formatted output programs telix minicom control modem local terminal let user interact remote servers internet telnet ssh work similarly simplest form text terminal like file writing file displays text reading file produces user enters unix-like operating systems several character special files correspond available text terminals operations special escape sequences control characters codice_1 functions program use easily via library ncurses complex operations programs use terminal specific ioctl system calls application simplest way use terminal simply write read text strings sequentially output text scrolled last several lines typically 24 visible unix systems typically buffer input text enter key pressed application receives ready string text mode application need know much terminal many interactive applications sufficient one common enhancements command line editing assisted libraries readline also may give access command history helpful various interactive command line interpreters even advanced interactivity provided full-screen applications applications completely control screen layout also respond key-pressing immediately mode useful text editors file managers web browsers addition programs control color brightness text screen decorate underline blinking special characters e.g box drawing characters achieve application must deal plain text strings also control characters escape sequences allow move cursor arbitrary position clear portions screen change colors display special characters also respond function keys great problem many different terminals terminal emulators set escape sequences order overcome special libraries curses created together terminal description databases termcap terminfo dumb terminals interpret limited number control codes cr lf etc ability process special escape sequences perform functions clearing line clearing screen controlling cursor position context dumb terminals sometimes dubbed glass teletypes essentially limited functionality mechanical teletype type dumb terminal still supported modern unix-like systems setting environment variable term dumb smart intelligent terminals also ability process escape sequences particular vt52 vt100 ansi escape sequences graphical terminal display images well text graphical terminals divided vector-mode terminals raster mode vector-mode display directly draws lines face cathode-ray tube control host computer system lines continuously formed since speed electronics limited number concurrent lines displayed one time limited vector-mode displays historically important longer used practically modern graphic displays raster-mode descended picture scanning techniques used television visual elements rectangular array pixels since raster image perceptible human eye whole short time raster must refreshed many times per second give appearance persistent display electronic demands refreshing display memory meant graphic terminals developed much later text terminals initially cost much terminals today graphical show images screen modern term graphical terminal thin client thin client typically uses protocol like x11 unix-terminals rdp microsoft windows bandwidth needed depends protocol used resolution color depth modern graphic terminals allow display images color text varying sizes colors fonts type faces early 1990s industry consortium attempted define standard alphawindows would allow single crt screen implement multiple windows behave distinct terminal unfortunately like i2o suffered run closed standard non-members unable obtain even minimal information realistic way small company independent developer could join consortium possibly standard disappeared without trace terminal emulator piece software emulates text terminal past widespread use local area networking broadband internet access many computers would use serial access program communicate computers via telephone line serial device first macintosh released program called macterminal used communicate many computers including ibm pc dec terminal one first terminal programs popular altair win32 console windows emulate physical terminal supports escape sequences ssh telnet programs logging textually remote computers windows including telnet program bundled versions windows often incorporate code process escape sequences terminal emulators unix-like systems example gnome-terminal qterminal xterm terminal.app emulate physical terminals including support escape sequences e.g xterm emulate vt220 tektronix 4010 hardware terminals terminals operate various modes relating send input typed user keyboard receiving system whatever may distinction keys multiple-mode terminals switch modes pressing key block mode thing pressing key whilst key cause input line sent host line-at-a-time mode key rather cause terminal transmit contents character row cursor currently positioned host host-issued prompts different computer operating systems require different degrees mode support terminals used computer terminals posix terminal interface provided unix posix-compliant operating systems accommodate block-mode terminals rarely requires terminal line-at-a-time mode since operating system required provide canonical input mode terminal device driver operating system emulates local echo terminal performs line editing functions host end usually especially host system support non-canonical input mode terminals posix-compliant systems always character-at-a-time mode contrast ibm 3270 terminals connected mvs systems always required block mode block-oriented terminal block mode terminal type computer terminal communicates host blocks data opposed character-oriented terminal communicates host one character time ibm 3270 perhaps familiar implementation block-oriented terminal mainframe computer manufacturers several companies produced block-oriented terminals typically incorporate buffer stores one screen data also stores data attributes indicating appearance color brightness blinking etc also marks data enterable terminal operator vs. protected entry allowing entry numeric information vs. allowing characters etc typical application host sends terminal preformatted panel containing static data fields data may entered terminal operator keys data updates database entry appropriate fields entry complete enter pf key pressed 3270 block data usually data entered operator modified data sent host one transmission 3270 terminal buffer device could updated single character basis necessary existence set buffer address order sba usually preceded data written/overwritten within buffer complete buffer could also read replaced using codice_2 command codice_3 command unformatted formatted case 3270 block-oriented terminals cause less system load host less network traffic character-oriented terminals also appear responsive user especially slow connections since editing within field done locally rather depending echoing host system early terminals limited editing capabilities – 3270 terminals example could check entries valid numerics subsequent smart intelligent terminals incorporated microprocessors supported local processing programmers block-oriented terminals often used technique storing context information transaction progress screen possibly hidden field rather depending running program keep track status precursor html technique storing context url data passed arguments cgi program unlike character-oriented terminal typing character last position screen usually causes terminal scroll one line entering data last screen position block-oriented terminal usually causes cursor wrap — move start first enterable field programmers might protect last screen position prevent inadvertent wrap likewise protected field following enterable field might lock keyboard sound audible alarm operator attempted enter data field allowed
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Operating systems
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system image computing system image serialized copy entire state computer system stored non-volatile form file system said capable using system images shut later restored exactly state cases system images used backup hibernation example uses image entire machine ram system state written disk system image produced simply copying disk file elsewhere often disk cloning applications many systems complete system image created disk cloning program running within system information held outside disks volatile memory example non-volatile memory like boot roms process image copy given process state given point time often used create persistence within otherwise volatile system common example database management system dbms dbms store state database databases file closed see database dump dbms restarted later information database intact proceed though software never stopped another example would hibernate feature many operating systems state ram memory stored disk computer brought energy saving mode later restored normal operation emulators provide facility save image system emulated video gaming often referred savestate another use code mobility mobile agent migrate machines state saved copying data another machine restarting programming languages provide command take system image program normally standard feature smalltalk inspired flex lisp among languages development languages often quite different many programming languages example lisp programmer may load packages code running lisp implementation using read-eval-print loop usually compiles programs data loaded running lisp system programmer may dump system image containing pre-compiled possibly customized code—and also loaded application data often image executable run machines system image form executable programs distributed—this method often used programs tex emacs largely implemented lisp smalltalk idiosyncratic languages avoid spending time repeating initialization work every time start similar lisp machines booted lisp images called worlds world contains complete operating system applications data single file also possible save incremental worlds contain changes base world saving world lisp machine operating system could optimize contents memory better memory layout compacting data structures sorting data ... although purpose different system image often similar structure core dump
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Operating systems
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epson equity epson equity series ibm compatible personal computers manufactured 1985 early '90s epson inc. epson well known dot matrix printers time equity series represents entry growing pc compatible market equity first system introduced equipped intel 8088 cpu one two 5.25 floppy disk drives original equity no-frills offering ran pc standard 4.77 mhz clock rate came 256 kb ram expansion 512 kb required expansion board displayed cga video available expansion slots two half-height drive bays lacked socket 8087 math chip subsequent versions equity i+ apex 100 upped clock rate 10 mhz standard ram 640 kb supported 3.5 inch floppy drives hard disks sported 8087 socket display circuitry monochrome hercules graphics adapter epson bundled utility programs offered decent turnkey functionality novice users equity reliable compatible design half price similarly-configured ibm pc epson often promoted sales bundling one printers cost equity sold well enough warrant furtherance equity line follow-on equity ii equity iii others based i386sx
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Computer architecture
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multics relational data store multics relational data store mrds short first commercial relational database management system written pl/1 honeywell multics operating system first sold june 1976 unlike sql systems emerged late 1970s early 80 mrds used command language basic data manipulation equivalent codice_1 codice_2 statements sql operations like creating new database general file management required use separate command program
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Operating systems
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samhain software samhain integrity checker host intrusion detection system used single hosts well large unix-based networks supports central monitoring well powerful new stealth features run undetected memory using steganography
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Computer security
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metasyntactic variable metasyntactic variable specific word set words identified placeholder computer science specifically computer programming words commonly found source code intended modified substituted applicable specific usage compilation translation executable words foo bar good examples used 330 internet engineering task force requests comments documents explaining foundational internet technologies like http websites tcp/ip email protocols mathematical analogy metasyntactic variable word variable words algebra letters used variables numbers metasyntactic variables used name entities variables functions commands whose exact identity unimportant serve demonstrate concept useful teaching programming due english foundation-language lingua franca computer programming languages variables commonly seen even programs examples programs written spoken-language audiences typical names may depend however subculture developed around given programming language metasyntactic variables used commonly across programming languages include foobar foo bar baz qux quux quuz corge grault garply waldo fred plugh xyzzy thud several words references game colossal cave adventure wibble wobble wubble flob also used uk complete reference found mit press book titled hacker dictionary spam ham eggs principal metasyntactic variables used python programming language reference comedy sketch spam monty python eponym language japanese words hoge ほげ piyo ぴよ commonly used common words variants fuga ふが hogera ほげら hogehoge ほげほげ note -ra pluralizing ending japanese reduplication also used pluralizing origin hoge metasyntactic variable known believed date early 1980s french word toto widely used variants tata titi tutu related placeholders one commonly-raised source use toto reference stock character used tell jokes tête à toto following example function name foo variable name bar metasyntactic variables lines beginning // comments spam ham eggs principal metasyntactic variables used python programming language reference famous comedy sketch spam monty python eponym language following example spam ham eggs metasyntactic variables lines beginning comments ietf rfcs computer programming languages rendered plain text making necessary distinguish metasyntactic variables naming convention since would obvious context plain text example rfc 772 cited rfc 3092 contains instance another point reflected example convention metavariable uniformly substituted instance appearances given schema contrast nonterminal symbols formal grammars nonterminals right production substituted different instances section includes bits code show metasyntactic variables used teaching computer programming concepts function prototypes different argument passing mechanisms example showing function overloading capabilities c++ language
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Programming language topics
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deep instinct deep instinct cybersecurity company applies deep learning cybersecurity company implements advanced artificial intelligence task preventing detecting malware deep instinct founded 2014 guy caspi dr. eli david nadav maman headquarters company located new york city nvidia investor april 2019 deep instinct commissioned art project titled persistence chaos chinese artist guo dong consisting laptop infected 6 pieces malware represented 95 billion damages art auctioned final bid 1,345,000
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Computer security
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service request block service request block srb data structure mvs/370 successor versions ibm mainframe operating systems employed mainly exclusively start input/output interface srb may considered abstract highly optimized task control block tcb one associated resources access processor system resources utilized srb must accessed use branch entries new entries traditional system services formerly accessed exclusively using svc instructions srb may employ purpose abnormally terminating case svc 13 abend may used however branch entry abterm really appropriate employed start input/output interface srb always paired input/output supervisor block iosb otherwise employed srb facilitates inter -address-space communication general inter -application communication particular srbs may also employed intra -address-space processes highest possible performance required case necessary resources first acquired tcb usually job step tcb srbs scheduled i.e. presented system dispatcher compete processor resources conceivable address space may one tcb job step tcb tens hundreds even thousands srbs srbs performing almost work address space tcb merely synchronizing srbs responding communications system operator purposes synchronization tcb usually issue waitr svc 1 specifying list event control blocks ecbs one ecb per srb plus one system operator srb indicate completion tcb using branch entry post system service normally svc 2 special case would call address contained cvt0pt01 specifying ecb associated srb possibly message tcb message present often placed lowest 24 bits ecb otherwise unused highest eight bits used system disk device access network device access available srbs using improved control interval processing feature vsam fast path feature vtam respectively introduction mvs/370 successor systems whole new environment introduced service request block srb generally higher priority tcb indeed two distinct priorities global srb priority local address space srbs tcbs local srb priority local address space tcbs mvs dispatcher must manage absolute consistency across many two processors mvs/370 many sixteen processors successor systems sixteen processors available z/system models z/system support ziip dramatically increased use srbs traditional start input/output usage srb highly-optimized instance process control block mvs/370 successor systems tcb general-purpose instance process control block os/360 successor systems
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Operating systems
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lsof lsof command meaning list open files used many unix-like systems report list open files processes opened open source utility developed supported victor a. abell retired associate director purdue university computing center works supports several unix flavors open files system include disk files named pipes network sockets devices opened processes one use command disk unmounted unspecified files use listing open files consulted suitably filtered necessary identify process using files view port associated daemon one see sendmail listening standard port 25 one also list unix sockets using codice_1 lsof output describes
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Computer file systems
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digital notam digital notam digitam data set made available digital services containing information concerning establishment condition change aeronautical facility service procedure hazard timely knowledge essential systems automated equipment used personnel concerned flight operations digital notam encoding based aeronautical information exchange model aixm version 5 developed cooperation european organisation safety air navigation eurocontrol united states federal aviation administration faa support international ais community.the digitam eliminates free form text contained within notam replaces text series structured facts obtain aeronautical entity concerned 2012 federal aviation administration faa successfully launched first global digital notam notice airmen system airports airplanes united states
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Databases
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oasis tosca topology orchestration specification cloud applications tosca oasis standard language describe topology cloud based web services components relationships processes manage tosca standard includes specifications describe processes create modify web services 16 january 2014 oasis tosca technical committee approved tosca 1.0 standard commercialization cloud computing offerings required manageability tenant applications particularly large scale vendors offer services wide market written related standards predate developed concurrently oasis tosca standard aws cloudformation template json data standard allow cloud application administrators define collection related aws resources worth noting cloudformation proprietary format aws tosca based therefore bring promise oasis tosca targeting check grammar compared oasis tosca one openstack foundation also defined similar standard specifying resources orchestrations managing infrastructure application lifecycles heat-translator project one first adopt tosca standardized templating cloudify open source tosca-based orchestration framework based yaml alien4cloud meaning application lifecycle enabler cloud open source tosca based designer cloud application lifecycle management platform natively integrated cloudify runtime orchestration though orchestrators plugged ubicity provides tooling orchestrators based tosca seaclouds eu fp7 funded project whose mission provide seamless adaptive multi-cloud management service-based applications natively supports tosca participating standardization standard dice eu h2020 funded project offering model-driven devops toolchain develop big data applications tosca acts pivot language dev- modelling notations -ops space i.e. deployment monitoring etc particular offering standard infrastructure-as-code generated automatically models
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Web technology
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snowden effect snowden effect part reactions global surveillance disclosures made edward snowden subject controversy snowden variously called hero whistleblower dissident patriot traitor july 2013 media critic jay rosen defined snowden effect direct indirect gains public knowledge cascade events reporting followed edward snowden leaks classified information surveillance state u.s. december 2013 nation wrote snowden sparked overdue debate national security individual privacy 2014 world economic forum internet experts saw news microsoft would let foreign customers store personal data servers outside america sign snowden leaks leading countries companies erect borders cyberspace forbes effect seen nearly united u.s. congress opposition massive post-9/11 domestic intelligence gathering system spring 2014 global attitudes survey pew research center found snowden disclosures tarnished image united states especially europe latin america may 2014 obama administration appointed william evanina former fbi special agent counter-terrorism specialty new government-wide national counterintelligence executive instead getting carried away concept leakers heroes evanina said august need get back basics means loyal undifferentiated unauthorized leaking criminal act dealing insider threats intelligence community priority since wikileaks published chelsea manning disclosures 2010 evanina said aftermath snowden june 2013 revelations process sped regional railway acela train year later 100,000 fewer people security clearances september 2014 director national intelligence james clapper said snowden leaks created perfect storm degrading intelligence community capabilities snowden leaks said clapper damaged relationships foreign corporate stakeholders restrained budget resources caused u.s. discontinue collecting intelligence certain targets putting united states greater risk october 2014 former director national counterterrorism center matthew g. olsen told cnn snowden disclosures made easier terrorist groups evade u.s. surveillance changing encryption methods olsen said intelligence collection individuals concern lost preventing insight activities july 2015 isil studied snowden disclosures said u.s. officials leaders using couriers encrypted communications western analysts could crack february 2015 national counterterrorism center director nicholas rasmussen told congress snowden disclosures damaged u.s. intelligence capabilities rasmussen said government knew specific terrorists learning snowden leaks u.s. collected intelligence increased security measures using new types encryption changing email addresses abandoning prior methods communicating reflecting effect leaks snowden wrote february 2015 biggest change awareness 2013 said nsa making records everybody phonecalls gchq monitoring lawyers journalists people raised eyebrows called conspiracy theorist days march 2015 usa today reported snowden effect hit guardian journalist michael wolff wrote guardian many years asserted recent selection katharine viner editor-in-chief read part deeply equivocal response part paper staff unusual power process selecting new editor snowden story according wolff developed sense journalistic queasiness around snowden difficult express party-line guardian questioning snowden retreat russia protection vladimir putin internally verboten technology industry snowden effect profound impact revealed nsa tapping information held u.s. cloud-based services google cisco lost business internationally due public outcry roles nsa spying study information technology innovation foundation published august 2013 estimated cloud-based computing industry could lost 35 billion 2016 wall street journal named snowden effect 2013 top tech story saying snowden leaks taught businesses convenience cloud cuts ways journal predicted effect would top 2014 news well given number documents yet revealed china profitable country u.s. tech companies suspicion either witting unwitting collaborators nsa spying according director research center chinese politics business indiana university effect also seen changes investment industry security back map according hussein kanji venture capitalist hoxton ventures august 8 2013 lavabit secure email provider snowden used discontinued service asked encryption keys would exposed u.s. government prosecutors emails 410,000 lavabit users next day similar provider called silent circle announced would shut possible sufficiently secure email october 2013 two companies joined forces announced new email service dark mail alliance designed withstand government surveillance revelations german chancellor angela merkel mobile tapped tech industry rushed create secure cell phone according techrepublic revelations nsa leaks rocked world chilling effect three biggest impacts seen increased interest encryption business leaving u.s. companies reconsideration safety cloud technology blackphone new yorker called phone age snowden —described smartphone explicitly designed security privacy created makers geeksphone silent circle pgp provided encryption phone calls emails texts internet browsing. ref name= kopstein/new yorker /ref since snowden disclosures americans used internet less things like email online shopping banking according april 2014 poll also april 2014 former nsa deputy director col. cedric leighton told bloomberg enterprise technology summit new york city snowden leaks performed significant disservice worldwide health internet leading brazil countries reconsider internet decentralized nature leighton suggested nation states efforts create versions internet beginning end internet know situation sudden everyone goes 'tribal mode—a german cloud swiss cloud separate internet—they significant nationalistic attempts said leighton happened snowden excuse policy excuse re-nationalize internet march 2014 new york times reported economic fallout snowden leaks boon foreign companies detriment u.s. firms daniel castro senior analyst information technology innovation foundation predicted united states cloud computing industry could lose 35 billion 2016 matthias kunisch german software executive switched u.s. cloud computing providers deutsche telekom said due snowden customers thought american companies connections nsa security analysts estimated u.s. tech companies since snowden collectively spent millions possibly billions dollars adding state-of-the-art encryption features consumer services cables link data centers july 2014 nonpartisan new america foundation summarized impact snowden revelations u.s. businesses erosion trust said report serious consequences u.s. tech firms executives france hong kong germany uk u.s. confirmed snowden leaks directly impacted companies around world think information communication technologies particularly cloud computing quarter british canadian multinational companies surveyed moving data outside u.s among u.s. companies attributing drops revenue part fallout snowden leaks cisco systems qualcomm ibm microsoft hewlett-packard proposed laws dozen foreign countries including germany brazil india would make harder u.s. firms business european union considering stricter domestic privacy legislation could result fines penalties costing u.s. firms billions dollars august 2014 massachusetts-based web intelligence firm recorded future announced found direct connection snowden leaks dramatic changes islamist terrorists interacted online 2010 privately held recorded future received investment in-q-tel nonprofit venture capital firm whose primary partner cia months snowden 2013 leaks said recorded future operatives al-qaeda associated groups completely overhauled 7-year-old encryption methods included homebrewed algorithms adopting instead sophisticated open-source software newly available downloads enabled encryption cellphones android products macs help disguise communications september 2014 seattle-based deep web dark web monitoring firm flashpoint global partners published report found little open source information available via jihadi online social media indicating snowden leaks impelled al-qaeda develop secure digital communications underlying public encryption methods employed online jihadists report concluded appear significantly changed since emergence edward snowden major recent technological advancements focused primarily expanding use encryption instant messenger mobile communications mediums may 2015 nation reported fallout edward snowden fiasco n't political—it largely economic soon extent nsa data collection became public overseas customers including brazilian government started abandoning u.s.-based tech companies droves privacy concerns dust n't settled yet tech-research firm forrester estimated losses may total 'as high 180 billion 25 percent industry revenue september 2014 new york times credited apple inc. update ios 8 encrypts data inside demonstrating snowden impact begun work way consumer products revelations said times killed recent efforts expand law also made nations around world suspicious every piece american hardware software—from phones servers made cisco systems—have 'back doors american intelligence law enforcement times situated development within post snowden era apple would longer comply nsa law enforcement requests user data instead maintaining apple n't possess key unlock data iphone however since new security protects information stored device data stored apple icloud service apple still able obtain customer information stored icloud response government requests times added google android would encryption enabled default upcoming versions
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Computer security
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qualcomm wi-fi son qualcomm wi-fi son self-organizing network solution developed qualcomm wi-fi networks simply automatically select link different wireless networking devices together using concept mesh networking supposed improve network coverage different corners house apartment also provide improved security note technology behind solution like mesh networking cellular self-organizing network would included dynamical adjustment different access points client devices
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Distributed computing architecture
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chris klaus christopher w. klaus born 1973 sarasota florida american technology entrepreneur founder cto internet security systems iss company started early 1990s sold ibm 2006 1.3b 2016 ceo kaneva game company founded 2004 also main financier multiple business accelerators atlanta area klaus formed iss early 1990s student georgia institute technology eventually dropping focus growing company 2004 stepped role chief technology officer iss pursue interests although remained significant shareholder retained role company chief security advisor 2006 iss sold ibm 1.3b around 2007 klaus became one georgia tech visible contributors giving 15m naming gift build college computing new home klaus advanced computing building july 2014 klaus co-founded neurolaunch business accelerator focused towards neurotech companies atlanta october 2015 financed co-founded another accelerator cyberlaunch focuses cybersecurity machine learning startups klaus wife crissy also prominent figure fifteen years work local marketing real estate well extensive work non-profit organizations recently founded fio360 atlanta first eco-early care center
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Computer security
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nosqlz nosqlz consistent key-value big data store nosql database z/os ibm systems developed systems programmer thierry falissard 2013 purpose provide low-cost alternative proprietary mainframe dbms version 1 free software nosqlz provides basic create read update delete crud functions designed straightforward easy implement acid properties provided real transactions optimistic concurrency control timestamp-based concurrency control multiversion concurrency control mvcc unlike version 1 version 2 nosqlz chargeable supports ibm parallel sysplex nosqlz dbms interfaced rexx cobol ibm high level assembler etc
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Databases
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sms spoofing sms spoofing technology uses short message service sms available mobile phones personal digital assistants set message appears come replacing originating mobile number sender id alphanumeric text spoofing legitimate uses setting company name message sent setting mobile number product name illegitimate uses impersonating another person company product also send mysterious messages look like legitimate numbers contacts sms spoofing occurs sender manipulates address information often done order impersonate user roamed onto foreign network submitting messages home network frequently messages addressed destinations outside home network – home smsc essentially “ hijacked ” send messages networks advanced cases even hijack existing contacts phone impact activity threefold legitimate use cases sms spoofing include sms spoofing attack often first detected increase number sms errors encountered bill-run errors caused spoofed subscriber identities operators respond blocking different source addresses gateway-mscs fraudsters change addresses easily by-pass measures fraudsters move using source addresses major interconnect partner may become unfeasible block addresses due potential impact normal interconnect services 2007 uk premium rate regulator phonepayplus formerly icstis concluded public consultation anonymous sms stated averse operation services however 2008 phonepayplus introduced new regulation covering anonymous sms requiring anonymous sms service providers send follow-up message recipient stating spoofed sms sent operate complaints helpline illegal send anonymous sms messages australia user prove sms sessions spoofed contact law enforcement cellular provider able track sms messages actually sent user may also modify phone settings messages authorized numbers allowed always effective since hackers could impersonating user friends well
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Computer security
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caldera openlinux caldera openlinux col defunct linux distribution originally introduced caldera 1997 based german lst power linux distribution taken developed caldera systems sco group since 1998 successor caldera network desktop put together caldera since 1995 openlinux early business-oriented distribution foreshadowed direction developments came distributions linux community generally corsair user interface netware project run novell corporation advanced technology group atg 1993 1995 novell wanted desktop environment internet connectivity conducted research better easily integrate manage network access users windows support connecting novell networks would improved later releases internet dominated unix-based operating systems relative needs novell deemed unixes day hardware intensive large charged much license fees group became convinced linux offered best possible answer os component many components well particular interest 5 april 1994 board novell hired robert frankenberg general manager hewlett-packard personal information products group replace raymond john noorda ceo novell novell stock price performed poorly recently due flagging growth novell network division nsg growing pace 19 per year unix business division usg flat desktop applications division dsg shrinking rate 400 million per year frankenberg initiative refocus company networking networking services terms corsair meant shedding pieces advanced technology group disbanded shut willows os project negotiations started would eventually lead wordperfect sold corel january 1996 ferret line new direction component kept within novell noorda family trust nft ray noorda founded venture capital investment group called canopy group two years earlier 1992 thought substantial promise os project willows project created two companies continue work started novell api company called willows software inc. founded 1993 os company became caldera inc. founded october 1994 incorporated january 1995 noorda early vision caldera create ipx-based version linux would license key components resell technology back novell continue internet desktop effect 1994 caldera started life kind outsourcing project novell based technology demo named exposé caldera started ten employees novell bryan wayne sparks founder/president novell bryce j. burns chief operations officer novell ransom h. love vp marketing novell greg page vp engineering bell labs craig bradley vp sales lotus word perfect point 1995 ransom love ray noorda took note technologies caldera put together specifically component novell caldera assembled components needed create var platform however caldera faced bootstrapping problem oem var applications often depended crucially companies commercial applications since applications n't ported linux yet could n't meaningfully port applications caldera responded creating binary applications package allowed linux run unixware openserver applications linux application binary interface abi project assisting santa cruz operation sco creating linux kernel personalities linux kernel personalities worked bring linux application compatibility sco unix formerly unixware openserver idea enable developers write unix linux common application programming interface api common application binary interface abi way developers n't work hard unix users client base inherited sco could run linux applications caldera also supported alan cox work smp linux displaced unix intel x86 platform sun microsystems would n't low-end unix path point becomes interesting light sco litigation eight years later ibm 2003 ibm company involved smp work moreover company directly involved company later became sco group essentially sco suing ibm work 1995 xfree86 still hard configure unreliable chipsets caldera shipped metrolink motif xi graphic accelerated-x known releases caldera network desktop produced sold march 1997 1996 caldera continued valuable player example 23 may 1996 linux kongress berlin germany caldera announced plans obtain posix fips certifications x/open brand unix 95 xpg4 base 95 linux operating system kernel open linux contrast cnd openlinux based lst power linux slackware-derived distribution maintained linux support team since 1993 first come linux 2.0 kernel 1996 linux support team grew stefan probst ralf flaxa company lst software gmbh lst standing linux system technology erlangen germany openlinux development led become caldera german development center caldera deutschland gmbh since may 1997 23 july 1996 caldera purchased novell dos remaining digital research assets novell order bundle dos version linux led creating opendos distribution help port dos applications caldera supported linux-port staroffice 3.1 ca 800.000 dm order offer product forthcoming openlinux distribution 1997 1997 openlinux distribution first released caldera taken form would remembered caldera switched high end linux product business linux distribution became rich features bundled proprietary software however became less community oriented released less frequently linuxes differences included automated configuration administration tools paid technical support staff built-in consistent default gui range supported applications next five years caldera systems offered additional commercial extensions linux licensed sun wabi allow people run windows applications linux additionally shipped linux versions wordperfect novell later corel coreldraw since many customers used dual boot setup fips unreliable shipped powerquest partitionmagic allow customers non-destructively repartition hard disks partnership ibm produced first linux distribution db2 compatible oracle corporation became target platform linux port oracle database ventures included starting blackdown java project creating professional certification also formed strong partnerships sco value-added reseller market started laying groundwork oem sales unix-based vertical applications caldera systems offered three versions openlinux addition people applications created many linux extensions fill voids commercial company caldera systems began working linux equivalent replacing microsoft exchange server microsoft outlook would eventually become volution messaging server offered calendaring/scheduling options shared busy/free information ssl support e-mail easy configuration additionally caldera deutschland created first fully graphical installer linux called lizard starting november 1998 invented browser-based unix system administration created webmin project employed developer jamie cameron 1999 2001 caldera systems created full featured gui system administration tool called caldera open administration system coas tool unified easy use administration tool modular design scalability broad scope abilities featured openlinux showed linux community would required create mainstream desktop os linux kernel many ways last ten years desktop progress successfully implement caldera attempting tools available using open source software place closed applications technique utilize commercial software fill largest gaps making product value add thus could charge made commercial time made advanced distribution available desktop company became caldera international direction ransom love focus desktop company became mainly marketing business relationships several reasons first caldera 280 million lawsuit microsoft dr-dos flush cash secondly caldera distribution good primary advantages use technologies owned caldera thus caldera successful success could technical standpoint imitated red hat suse turbolinux etc third years caldera competing directly sco unix 1997 linux outperformed sco almost every respect making choice switch sco caldera no-brainer companies also meant switch vendors support organizations caldera sco acquisition aimed eliminating problem caldera international corporate direction became combine sco distribution marketing var arm lamp use project monterey develop 64-bit strategy sco offered technical standpoint however caldera openlinux really shone ransom love years commercial bundling solution continued work powerful low bug linux standards distribution worked well wide range hardware charged great deal relative distributions able generate strong profit red hat pulled way ahead terms us sales global sales front trailed suse turbolinux well financially due dr-dos settlement strongest linux distributions known releases incomplete products caldera systems quickly found classic business problem interests existing business conflicted growth model santa cruz operation sco much larger company caldera systems fact 71 million revenue 90 sco side business moreover caldera systems costs 4 marketing generate 1 sales sco mature sold mainly repeat customers var relationship even problematic caldera systems always sold linux sco better model done everything possible make transition sco caldera systems relatively seamless 14,000 sco resellers made much sco sale sales caldera systems anxious move existing customers sco linux even supportive linux saw strong value add caldera systems often sold red hat enterprise linux caldera systems two businesses direct competition one shrinking still profitable unix business rapidly growing business still hemorrhaging money logical solution establish caldera systems premier linux brand without threat red hat transitioning resellers sco caldera systems would much easier mind ransom love formed alliance large business oriented linux distributions utilized kde desktop called united linux alliance comprised caldera international suse linux turbolinux conectiva filings novell sco group sco v. novell lawsuit showed simply marketing gimmick real alliance business responded favorably movement ibm amd quickly formed partnerships linux professional institute adopted united linux standard distribution training first time linux distribution suse linux engineering continued maintain large technical staff caldera international global support organization turbo linux well conectiva brought growth potential less flooded markets merger successful love sparks could claim vindication year novell reversed frankenberg decision brought united linux engineering talent back fold acquisition suse united linux rejected broader linux community use per-seat licensing highly controversial decision importantly time united linux released darl mcbride become ceo caldera international focus shifted away linux caldera international point released caldera linux distribution openunix 8 kernel instead linux kernel unix tli streams support made writing drivers easier caldera international proved replacing kernel yet change much else full featured desktop server linux 2002 caldera international board directors including ralph yarro named darl mcbride formerly franklin-covey ceo almost immediately saw value caldera international primarily value sco company renamed sco group ransom love reassigned work exclusively united linux completed left company join progeny linux systems aiming create professional debian remained capacity board member advisor 30 april 2007 progeny ceased operations mcbride began focus sco copyrights one mcbride first acts ceo collect 600,000 back licensing fees owed caldera international cleaned various linux-related licensing issues allowing new round financing soon thereafter made strong accusations linux infringed copyrights sco held unix claimed purchased copyrights novell novell denied selling unix copyright prompting sue slander title sco also initiated lawsuits ibm autozone alleging copyright infringements use distribution linux none lawsuits resolved sco created division scosource owns licenses intellectual property desktop license 699
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Operating systems
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geometric description language computer-aided design geometric description language gdl programming language archicad library parts gsm file format cad objects objects similar blocks autocad unlike blocks parametric 2d 3d features connected view one get correct visualization example side view section top view plan perspective 3d view gdl scripts define archicad library part main roles 3d model 3d model projected section/elevation 2d plan 2d plan view user interface display behaviour listing quantities versions archicad contain default libraries also objects like furniture windows doors trees people cars construction elements etc several commercial websites selling high-detailed intelligent parametric objects perhaps better variable default libraries example lot environmental objects like plants people garden elements included original software gdl free technology although archicad commercial software allowed possible develop gdl based object libraries using free tools like graphisoft lp_xmlconverter graphisoft gdl web plug-in gdl programming language basic-like control flow statements variable logic 2d 3d gdl model elements linked local right-handed coordinate system placing element desired position move coordinate system desired position orientation generate element every movement rotation stretching coordinate system called transformation transformations stored stack extended transformations cut deleting one transformations top gdl maintains forward compatibility means archicad library part readable every subsequent archicad program necessarily earlier versions
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Programming language topics
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lomac low water-mark mandatory access control lomac mandatory access control model protects integrity system objects subjects means information flow policy coupled subject demotion via floating labels lomac system subjects objects assigned integrity labels made one hierarchical grades depending types together label elements permit labels placed partial order information flow protections demotion decisions based dominance operator describing order
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Computer security
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graphical identification authentication graphical identification authentication gina component windows 2000 windows xp windows server 2003 provides secure authentication interactive logon services gina replaceable dynamically linked library loaded early boot process context winlogon machine started responsible handling secure attention sequence typically control-alt-delete interacting user sequence received gina also responsible starting initial processes user windows shell first log gina discontinued windows vista default gina library msgina.dll provided microsoft part operating system offers following features winlogon configured use different gina providing non-standard authentication methods smart card readers identification based biometrics provide alternate visual interface default gina developers implement replacement gina required provide implementations set api calls cover functionality displaying workstation locked dialog processing secure attention sequence various user states responding queries whether locking workstation allowed action supporting collection user credentials terminal services-based connections interacting screensaver custom gina could made entirely scratch original gina modifications custom gina specified placing string named ginadll registry location codice_1 winlogon component solely responsible calling apis gina library winlogon process starts compares version number supported loaded gina library gina library higher version winlogon windows boot done gina library written given version winlogon expect certain set api calls provided winlogon support replaceable gina dlls introduced windows nt server 3.51 windows nt workstation 4.0 sp3 successive versions windows introduced additional functionality winlogon resulting additional functionality implemented replacement gina windows 2000 example introduced support displaying status messages including verbose messages turned group policy current state user e.g applying computer settings starting applications user context facilitates restarting windows explorer automatically crashes well starting task manager windows xp introduced support fast user switching remote desktop interactive simplified user-friendly full-screen logon windows vista gina replaced credential providers allow significantly increased flexibility supporting multiple credential collection methods support use multiple gina models complex chaining method used required custom ginas often work fast user switching gina libraries work windows vista later windows versions one difference however gina could completely replace windows logon user interface credential providers
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Operating systems
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rtelnet rtelnet socks client version telnet unix-like systems rtelnet utility provides similar functionality telnet hosts behind firewall normally firewalls designed permit deny network transmissions based upon set rules network accessibility across firewall reduced order provide adequate security hosts within firewall many services directly access resources placed outside firewall rtelnet utility provides functionality telnet maintaining security requirement firewall nat though utility differs much counterpart implementation behaves almost indistinguishably users terms command interface communication scheme rtelnet versatile client used connections inside hosts directly outside hosts via socks proxy servers rtelnet starts prints version number name ip address default socks proxy server stderr stream channel consults configuration file /etc/socks.conf determine whether request allowed denied based requesting user destination host requested service allowable requests configuration file also dictates whether direct proxy connection used given destination optionally actual socks servers use proxy connection rtelnet utility requires libsocket.so shared library run rtelnet listed project sourceforge code repository
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Internet protocols
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archicad archicad architectural bim cad software macintosh windows developed hungarian company graphisoft archicad offers computer aided solutions handling common aspects aesthetics engineering whole design process built environment — buildings interiors urban areas etc development archicad started 1982 original apple macintosh following launch 1987 graphisoft virtual building concept archicad became regarded first implementation bim archicad recognized first cad product personal computer able create 2d 3d geometry well first commercial bim product personal computers considered revolutionary ability store large amounts information within 3d model today 120,000 users archicad complete design suite 2d 3d drafting visualization building information modeling functions architects designers planners wide range software applications integrated archicad cover design needs architectural office archicad allows user work data-enhanced parametric objects often called smart objects users differs operational style cad programs created 1980s product allows user create virtual building virtual structural elements like walls slabs roofs doors windows furniture large variety pre-designed customizable objects come program archicad allows user work either 2d 3d representation screen two-dimensional drawings exported time even though model program database always stores data three dimensions plans elevations sections generated three-dimensional virtual building model constantly updated user 'rebuilds view detail drawings based enlarged portions model 2d detail added archicad released first file exchange based teamwork solution version 5.1 1997 allowed architects work building model simultaneously completely rewritten teamwork 2.0 solution new database approach came version 13 2009 named graphisoft bim server since changes differences sent central storage solution allows remote access project internet thus allowing worldwide project collaboration coordination 2014 introduction bimcloud better integration provided standard solutions browser-based management ldap connection http/https based communication also new scalability options available allowing multi-server layouts created optional caching servers third-party vendors manufacturers architectural products compiled libraries architectural components use archicad program includes geometric description language gdl used create new components also api application programming interface odbc database connections supported third party add-on developers via direct api links 4d 5d software vico office suite tocoman ilink archicad model exported bim-based cost estimation scheduling archicad also directly linked via api solibri model checking quality assurance tools addition graphisoft provides direct link grasshopper 3d enabling visual programming environment parametric modelling design archicad import export dwg dxf ifc bcf files among others graphisoft active member buildingsmart formerly international alliance interoperability iai industry organization publishes standards file data interoperability built environment software graphisoft one founders open bim concept supports 3d bim data exchange different design disciplines open-source platforms archicad also export 3d model corresponding 2d drawings bimx format viewed number desktop mobile platforms native bimx viewers commercial educational fully functional 30-day trial versions installed installer long hardware protection present software activated trial educational serial number archicad launched demo mode installer files downloaded without registration educational trial serial numbers obtained registration archicad available number localized versions addition translated user interface documentation versions set parametric objects object libraries developed considering specific requirements regional market different default values object properties menu arrangements etc various free commercial add-on products extensions add extra functionality archicad provide data exchange possibilities software applications extensions developed graphisoft freely available trimble sketchup google earth maxon cinema 4d import/export add-ons extensions sold separately graphisoft mep modeler graphisoft ecodesigner graphisoft virtual building explorer number add-ons provided third party vendors cigraph cadimage detailed version history see help center article
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Operating systems
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malware information sharing platform malware information sharing platform misp open source threat intelligence platform project develops utilities documentation effective threat intelligence sharing indicators compromise several organizations run misp instances listed website project started around june 2011 christophe vandeplas frustration way many indicators compromise iocs shared email pdf documents parseable automatic machines home started play around cakephp made proof concept idea called cydefsig cyber defence signatures mid july 2011 presented personal project work belgian defence feedback rather positive giving access cydefsig running personal server belgian defence started use cydefsig officially starting mid august 2011 christophe allowed spend time cydefsig work-hours still working home point nato heard project january 2012 first presentation done introduce depth project looked products marked offered seemed deemed openness cydefsig great advantage andrzej dereszowski first part-time developer nato side one thing led another months later nato hired full-time developer improve code add features collaborative development started date many personal projects license explicitly written yet collaboratively decided project would released publicly affero gpl license share code many people possible protect harm project renamed misp malware information sharing project name invented alex vandurme nato january 2013 andras iklody became main full-time developer misp day initially hired nato evening week-end contributor open source project meanwhile organisations started adopt software promoted around cert world cert-eu circl many others nowadays andras iklody lead developer misp project works circl misp project expanded misp covering malware indicators also fraud vulnerability information name misp threat sharing includes core misp software myriad tools pymisp format core format misp taxonomies warning-lists support misp misp community project lead team volunteers project funded european union connecting europe facility computer incident response center luxembourg indicators compromise managed misp may originate variety sources including internal incident investigation teams intelligence sharing partners commercial intelligence sources commercial sources integration misp include symantec deepsight intelligence kaspersky threat feeds mcafee active response misp integrations open-source commercial threat intelligence platforms include eclecticiq platform
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Computer security
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macintosh iisi macintosh iisi personal computer designed manufactured sold apple computer inc. october 1990 march 1993 introduced lower-cost alternative macintosh ii family desktop models popular home use offered expandability performance macintosh lc introduced time like lc built-in sound support well support color displays maximum screen resolution 640×480 eight-bit color iisi remained market two half years discontinued shortly introduction replacement centris 610 iisi case design compact three-box desktop unit used macintosh model one macintosh models true positioned macintosh iici apple entry-level professional model iisi price lowered redesign motherboard substituting different memory controller deletion one expansion card slots single processor direct slot removal level 2 cache slot shipped either 40-mb 80-mb internal hard disk 1.44-mb floppy disk drive mc 68882 fpu optional upgrade mounted special plug-in card ports included scsi two serial ports adb port floppy drive port 3.5mm stereo headphone sound output microphone sound input sockets bridge card available iisi convert processor direct slot standard internal nubus card slot compatible machines macintosh ii family bridge card included math co-processor improve floating-point performance nubus card mounted horizontally motherboard cut costs iisi video shared main system memory also effect slowing video considerably especially iisi 1 mb slow ram soldered motherboard david pogue book macworld macintosh secrets observed one could speed video considerably one set disk cache size large enough force computer draw video ram faster ram installed simm banks iisi also suffers sound difficulties time speaker contacts fail causing sound periodically drop problem caused modular construction computer mono loudspeaker daughterboard motherboard springy contacts speaker vibrations led fretting touching surfaces problem could solved removing motherboard using pencil eraser clean contacts daughterboard holding loudspeaker iisi macintosh use case design issues never corrected subsequent model iisi designed easily cheaply manufactured tools required put one together – everything held place clips latches heritage cut-down iici simple modification substitute new clock crystal increase system clock rate 25 mhz slight increase performance charles bukowski enthusiastic user iisi
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Computer architecture
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webauthn webauthn web authentication web standard published world wide web consortium w3c webauthn core component fido2 project guidance fido alliance goal project standardize interface authenticating users web-based applications services using public-key cryptography client side support webauthn implemented variety ways underlying cryptographic operations performed authenticator abstract functional model mostly agnostic respect key material managed makes possible implement support webauthn purely software making use processor trusted execution environment trusted platform module tpm sensitive cryptographic operations also offloaded roaming hardware authenticator turn accessed via usb bluetooth low energy near-field communications nfc roaming hardware authenticator conforms fido client authenticator protocol ctap making webauthn effectively backward compatible fido universal 2nd factor u2f standard similar legacy u2f web authentication resilient verifier impersonation resistant active man-in-the-middle-attacks unlike u2f webauthn require traditional password moreover roaming hardware authenticator resistant malware since private key material time accessible software running host machine webauthn level 1 standard published w3c recommendation 4 march 2019 level 2 specification development fido2 successor fido universal 2nd factor u2f legacy protocol fido2 authentication advantages u2f—the primary difference fido2 authenticator also multi-factor authenticator fido2 authenticator may used either single-factor mode multi-factor mode single-factor mode authenticator activated test user presence usually consists simple button push multi-factor mode authenticator something performs user verification depending authenticator capabilities case authenticator performs user verification locally device secret biometric stored authenticator shared website moreover single secret biometric works websites authenticator select correct cryptographic key material use service requesting authentication user verification completed successfully secret biometric authenticator used together similarly would used smartphone example fingerprint used provide convenient access smartphone occasionally fingerprint access fails case pin used like predecessor fido u2f w3c web authentication webauthn involves website web browser authenticator webauthn specifies claimant demonstrates possession control fido2 authenticator verifier called webauthn relying party authentication process mediated entity called webauthn client little conforming web browser purposes illustration assume authenticator roaming hardware authenticator see options case authenticator multi-factor cryptographic authenticator uses public-key cryptography sign authentication assertion targeted webauthn relying party assuming authenticator uses pin user verification authenticator something pin something know initiate webauthn authentication flow webauthn relying party indicates intentions webauthn client i.e. browser via javascript webauthn client communicates authenticator using javascript api implemented browser roaming authenticator conforms fido client authenticator protocol webauthn strictly require roaming hardware authenticator alternatively software authenticator implemented smartphone e.g platform authenticator i.e. authenticator implemented directly webauthn client device may used relevant examples platform authenticators include windows hello android operating system illustrated flow relies pin-based user verification terms usability modest improvement ordinary password authentication practice use biometrics user verification improve usability webauthn logistics behind biometrics still poorly understood however lingering misunderstanding among users biometric data transmitted network manner passwords case webauthn relying party receives signed authentication assertion browser digital signature assertion verified using trusted public key user webauthn relying party obtain trusted public key first place obtain public key user webauthn relying party initiates webauthn registration flow similar authentication flow illustrated primary difference authenticator signs attestation statement attestation private key signed attestation statement contains copy public key webauthn relying party ultimately uses verify signed authentication assertion attestation statement also contains metadata describing authenticator digital signature attestation statement verified trusted attestation public key particular model authenticator webauthn relying party obtains store trusted attestation public keys unspecified one option use fido metadata service attestation type specified javascript determines trust model instance attestation type called self-attestation may desired trust model essentially trust first use webauthn level 1 standard published w3c recommendation web authentication working group 4 march 2019 webauthn supported following web browsers google chrome mozilla firefox microsoft edge apple safari preview webauthn also supported opera web browser desktop version google chrome supported webauthn since version 67 firefox fully supported previous fido u2f standard included enabled webauthn firefox version 60 released may 9 2018 early windows insider release microsoft edge build 17682 implemented version webauthn works windows hello well external security keys existing fido u2f security keys largely compatible webauthn standard though webauthn added ability reference unique per-account user handle identifier older authenticators unable store one first fido2-compatible authenticators second-generation security key yubico announced april 10 2018 first security level 2 certified fido2 key called goldengate announced one year later ewbm april 8 2019. dropbox announced support webauthn logins 2nd factor may 8 2018 webauthn implements extension w3c general credential management api attempt formalize interaction websites web browsers exchanging user credentials web authentication api extends credential management codice_1 codice_2 javascript methods accept codice_3 parameter codice_4 method used registering public key authenticators part associating user accounts possibly initial account creation time likely adding new security device existing account codice_5 method used authenticating logging check browser supports webauthn scripts check codice_6 interface defined addition codice_7 standard also defines codice_8 codice_9 codice_10 interfaces addition variety dictionaries datatypes api allow direct access manipulation private keys beyond requesting initial creation august 2018 paragon initiative enterprises security audit upcoming webauthn standard could find specific exploits revealed serious weaknesses way underlying cryptography used mandated standard main points criticism revolve around two potential issues problematic cryptographic systems past therefore avoided order fall victim class attacks paragon initiative enterprises also criticized way standard initially developed proposal made public advance experienced cryptographers asked suggestions feedback hence standard subject broad cryptographic research academic world despite shortcomings paragon initiative enterprises still encourage users continue use webauthn come recommendations potential implementors developers standard hope implemented standard finalized avoiding mistakes early possible would prevent industry challenges introduced broken standards need backwards compatibility ecdaa used combination device attestation particular feature webauthn necessarily required authentication work current implementations allow user decide whether attestation statement sent registration ceremony independently relying parties choose require attestation
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Computer security
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compaq presario v6000 compaq presario v6000 series widescreen 15.4 nowiki /nowiki laptop computers manufactured hewlett packard includes v6000z series based amd processors mobile sempron dual core turion x2 v6000t based intel processors repeated reliability issues amd based v6000z laptops fan algorithm bios misconfigured causing overheating damage wireless cards motherboard late 2007 hp extended limited warranty cover defects however date limited 2 years purchase product computer shows faults 2-year period hewlett packard repair despite fault cause australia resulted action queensland office fair trading hewlett packard misrepresenting customers rights resulting agreed au 3 million settlement computer available following processors max screen resolution 1280x800 nvidia geforce go 6150 intel x3100 depending cpu family nvidia geforce go 7150m intel gma 950 memory expandable 3 gb memory built wireless lan receiver intel r pro/wireless 3945abg broadcom equipped 802.1g bluetooth powered hp software upgrade windows 7 ultimate 32-bit possible problems reported many hp pavilion dv9000 laptop computers well
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Computer architecture
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stun session traversal utilities nat stun standardized set methods including network protocol traversal network address translator nat gateways applications real-time voice video messaging interactive communications stun tool used protocols interactive connectivity establishment ice session initiation protocol sip webrtc provides tool hosts discover presence network address translator discover mapped usually public internet protocol ip address port number nat allocated application user datagram protocol udp flows remote hosts protocol requires assistance third-party network server stun server located opposing public side nat usually public internet originally stun acronym simple traversal user datagram protocol udp network address translators title changed specification updated set methods published rfc 5389 retaining acronym stun tool communications protocols detect traverse network address translators located path two endpoints communication implemented light-weight client-server protocol requiring simple query response components third-party server located common easily accessible network typically internet client side implemented user communications application voice internet protocol voip phone instant messaging client basic protocol operates essentially follows client typically operating inside private network sends binding request stun server public internet stun server responds success response contains ip address port number client observed server perspective result obfuscated exclusive xor mapping avoid translation packet content application layer gateways algs perform deep packet inspection attempt perform alternate nat traversal methods stun messages sent user datagram protocol udp packets since udp provide reliable transport guarantees reliability achieved application-controlled retransmissions stun requests stun servers implement reliability mechanism responses reliability mandatory transmission control protocol tcp may used induces extra networking overhead security-sensitive applications stun may transported encrypted transport layer security tls application may automatically determine suitable stun server communications particular peer querying domain name system dns stun udp stuns tcp/tls server srv resource record e.g. _stun._udp.example.com standard listening port number stun server 3478 udp tcp 5349 tls alternatively tls may also run tcp port server implementation de-multiplex tls stun packets case stun server found using dns lookups standard recommends destination domain name queried address records aaaa would used default port numbers addition using protocol encryption tls stun also built-in authentication message-integrity mechanisms via specialized stun packet types client evaluated external address use candidate communicating peers sharing external nat address rather private address reachable peers public network communicating peers located different private networks behind nat peers must coordinate determine best communication path nat behavior may restrict peer connectivity even public binding known interactive connectivity establishment ice protocol provides structured mechanism determine optimal communication path two peers session initiation protocol sip extensions defined enable use ice setting call two hosts network address translation implemented via number different address port mapping schemes none standardized stun self-contained nat traversal solution applicable nat deployment scenarios work correctly tool among methods tool protocols dealing nat traversal notably traversal using relay nat turn interactive connectivity establishment ice stun work three types nat full cone nat restricted cone nat port restricted cone nat cases restricted cone port restricted cone nats client must send packet endpoint nat allow packets endpoint client stun work symmetric nat also known bi-directional nat often found networks large companies since ip address stun server different endpoint symmetric nat case nat mapping different stun server endpoint turn offers better results symmetric nat original specification stun rfc 3489 specified algorithm characterize nat behavior according address port mapping behavior algorithm reliably successful applicable subset nat devices deployed algorithm consists series tests performed application path diagram ends red box udp communication possible path ends yellow green box communication possible methods rfc 3489 proved unreliable cope plethora different nat implementations application scenarios encountered production networks stun protocol method updated rfc 5389 retaining many original specifications subset methods removing others
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Internet protocols
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jazz computer jazz computer architecture motherboard chipset design originally developed microsoft use developing windows nt design eventually used basis mips-based windows nt systems part microsoft intended nt portable various microprocessor architectures mips risc architecture chosen one first development platforms nt project late 1980s/early 1990s however around 1990 existing mips-based systems turbochannel-equipped decstation sgi indigo varied drastically standard intel personal computers ibm at—for example neither used isa bus common intel 386-class machines reasons microsoft decided design mips-based hardware platform develop nt resulted jazz architecture later microsoft sold architecture design mips computer systems inc. became mips magnum jazz architecture includes design simple enough powerful enough majority windows nt-capable mips systems based modified versions jazz architecture list systems less based jazz includes jazz systems designed partially comply advanced risc computing arc standard used arc firmware boot windows nt operating systems also ported various jazz implementations risc/os mips magnum also mips systems designed run windows nt comply arc standard nevertheless based jazz platform
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Computer architecture
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web data services web data services refers service-oriented architecture soa applied data sourced world wide web internet whole web data services enable maximal mashup reuse sharing structured data relational tables semi-structured information extensible markup language xml documents unstructured information rss feeds content web applications commercial data online business sources web data services environment applications may subscribe consume information provide publish information others consume applications serve consumer-subscriber and/or provider-publisher web data services include mobile computing web portals enterprise portals online business software social media social networks web data services may support business-to-consumer b2c business-to-business b2b information-sharing requirements increasingly enterprises including web data services soa implementations integrate mashup-style user-driven information sharing business intelligence business process management predictive analytics content management applications according industry analysts speed development web data services enterprises deploy technologies ease discovery extraction movement transformation cleansing normalization joining consolidation access presentation disparate information types diverse internal sources data warehouses customer relationship management crm systems external sources commercial market data aggregators web data services build industry-standard protocols interfaces formats integration patterns used soa web 2.0 web-oriented architecture representational state transfer rest addition operating public internet web data services may run solely within corporate intranets across b2b supply chains even span hosted software-as-a-service saas cloud computing environments
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Web technology
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vm operating system vm often vm/cms family ibm virtual machine operating systems used ibm mainframes system/370 system/390 zseries system z compatible systems including hercules emulator personal computers first version released 1972 vm/370 officially virtual machine facility/370 system/370 reimplementation earlier cp/cms operating system milestone versions included vm/sp current version z/vm still widely used one main full virtualization solutions mainframe market cms usually coupled vm name refers conversational monitor system single-user operating system developed provide conversational time-sharing vm heart vm architecture control program hypervisor called vm-cp usually cp sometimes ambiguously vm runs physical hardware creates virtual machine environment vm-cp provides full virtualization physical machine – including i/o privileged operations performs system resource-sharing including device management dispatching virtual storage management traditional operating system tasks vm user provided separate virtual machine address space virtual devices etc. capable running software could run stand-alone machine given vm mainframe typically runs hundreds thousands virtual machine instances vm-cp began life cp-370 reimplementation cp-67 reimplementation cp-40 running within virtual machine another guest operating system might one time cms capable running bare machine true operating system though configuration would unusual runs guest os vm cms relies hypervisor interface vm-cp perform file system operations request vm services paravirtualization interface ibm coined term hypervisor 360/65 later used diag handler cp-67 diagnose instruction '83 x—no mnemonic privileged instruction originally intended ibm perform built-in diagnostic functions model-dependent functions vm/370 repurposed communication virtual machine cp instruction contains two four-bit register numbers called rx ry contain operand storage addresses return codes passed diagnose interface two-byte code cp uses determine diagnose function perform available diagnose functions listed early history vm described articles cp/cms history cp/cms vm/370 reimplementation cp/cms made available 1972 part ibm system/370 advanced function announcement added virtual memory hardware operating systems system/370 series early releases vm vm/370 release 6 continued open source today considered public domain policy ended late 1970s chargeable vm/se vm/bse upgrades 1980 vm/system product vm/sp however ibm continued providing updates source form existing code many years cp-67 privileged instructions virtual machine cause program interrupt cp simulated behavior privileged instruction vm remained important platform within ibm used operating system development time-sharing use customers remained ibm operating system os dos families remained ibm strategic products customers encouraged run vm formed close working relationships continuing community-support model early cp/cms users meantime system struggled political infighting within ibm resources available project compared ibm efforts basic problem system seen ibm field sales level vm/cms demonstrably reduced amount hardware needed support given number time-sharing users ibm business selling computer systems melinda varian provides fascinating quote illustrating vm unexpected success marketing forecasts vm/370 predicted one 168 would ever run vm entire life product fact first 168 delivered customer ran cp cms ten years later ten percent large processors shipped poughkeepsie would destined run vm would substantial portion mid-range machines built endicott fifteen years passed would vm licenses mvs licenses pc dos version runs xt/370 later at/370 called vm/pc vm/pc 1.1 based vm/sp release 3 ibm introduced system/370 extended architecture 3081 customers faced need run production mvs/370 system testing mvs/xa machine ibm solution vm/xa migration aid used new start interpretive execution sie instruction run virtual machine sie automatically handled privileged instructions returned cp cases could n't handle processor resource/system manager pr/sm later 3090 also used sie several vm/xa products eventually supplanted vm/esa z/vm vm role changed within ibm hardware evolution led significant changes processor architecture backward compatibility remained cornerstone ibm mainframe family still uses basic instruction set introduced original system/360 need efficient use 64-bit zseries made vm approach much attractive vm also utilized data centers converting dos/vse mvs useful running mainframe aix linux platforms become increasingly important current z/vm platform finally achieved recognition within ibm vm users long felt deserved z/vm sites run thousands simultaneous virtual machine users single system z/vm first released october 2000 remains active use development ibm third parties offered many applications tools run vm examples include ramis focus spss nomad db2 rexx racf officevision current vm offerings run gamut mainframe applications including http servers database managers analysis tools engineering packages financial systems release 6 vm/370 control program number commands general users concerned defining controlling user virtual machine lower-case portions command optional early 1980s vm group within share ibm user group sought mascot logo community adopt part response ibm mvs users selecting turkey mascot hilariously chosen according legend mvs performance group early days mvs performance sore topic 1983 teddy bear became vm de facto mascot share 60 teddy bear stickers attached nametags cuddlier oldtimers flag newcomers friendly approached bears hit soon appeared widely bears awarded inductees order knights vm individuals made useful contributions community
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Operating systems
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simultaneous multithreading simultaneous multithreading smt technique improving overall efficiency superscalar cpus hardware multithreading smt permits multiple independent threads execution better utilize resources provided modern processor architectures name multithreading ambiguous multiple threads executed simultaneously one cpu core also multiple tasks different page tables different task state segments different protection rings different i/o permissions etc. although running core completely separated multithreading similar concept preemptive multitasking implemented thread level execution modern superscalar processors simultaneous multithreading smt one two main implementations multithreading form temporal multithreading also known super-threading temporal multithreading one thread instructions execute given pipeline stage time simultaneous multithreading instructions one thread executed given pipeline stage time done without great changes basic processor architecture main additions needed ability fetch instructions multiple threads cycle larger register file hold data multiple threads number concurrent threads decided chip designers two concurrent threads per cpu core common processors support eight concurrent threads per core really efficiency technique inevitably increases conflict shared resources measuring agreeing effectiveness difficult however measured energy efficiency smt parallel native managed workloads historical 130 nm 32 nm intel smt hyper-threading implementations found 45 nm 32 nm implementations smt extremely energy efficient even inorder atom processors modern systems smt effectively exploits concurrency little additional dynamic power even performance gains minimal power consumption savings considerable researchers shown extra threads used proactively seed shared resource like cache improve performance another single thread claim shows smt increase efficiency others use smt provide redundant computation level error detection recovery however current cases smt hiding memory latency increasing efficiency increasing throughput computations per amount hardware used processor design two ways increase on-chip parallelism fewer resource requirements one superscalar technique tries exploit instruction level parallelism ilp multithreading approach exploiting thread level parallelism tlp superscalar means executing multiple instructions time thread-level parallelism tlp executes instructions multiple threads within one processor chip time many ways support one thread within chip namely key factor distinguish look many instructions processor issue one cycle many threads instructions come example sun microsystems ultrasparc t1 known niagara november 14 2005 release multicore processor combined fine-grain multithreading technique instead simultaneous multithreading core issue one instruction time multithreading cpus around since 1950s simultaneous multithreading first researched ibm 1968 part acs-360 project first major commercial microprocessor developed smt alpha 21464 ev8 microprocessor developed dec coordination dean tullsen university california san diego susan eggers henry levy university washington microprocessor never released since alpha line microprocessors discontinued shortly hp acquired compaq turn acquired dec. dean tullsen work also used develop hyper-threading hyper-threading technology htt versions intel pentium 4 microprocessors northwood prescott intel pentium 4 first modern desktop processor implement simultaneous multithreading starting 3.06 ghz model released 2002 since introduced number processors intel calls functionality hyper-threading provides basic two-thread smt engine intel claims 30 speed improvement compared otherwise identical non-smt pentium 4 performance improvement seen application-dependent however running two programs require full attention processor actually seem like one programs slows slightly hyper-threading turned due replay system pentium 4 tying valuable execution resources increasing contention resources bandwidth caches tlbs re-order buffer entries equalizing processor resources two programs adds varying amount execution time pentium 4 prescott core gained replay queue reduces execution time needed replay system enough completely overcome performance hit latest imagination technologies mips architecture designs include smt system known mips mt mips mt provides heavyweight virtual processing elements lighter-weight hardware microthreads rmi cupertino-based startup first mips vendor provide processor soc based eight cores runs four threads threads run fine-grain mode different thread executed cycle threads also assigned priorities imagination technologies mips cpus two smt threads per core ibm blue gene/q 4-way smt ibm power5 announced may 2004 comes either dual core dual-chip module dcm quad-core oct-core multi-chip module mcm core including two-thread smt engine ibm implementation sophisticated previous ones assign different priority various threads fine-grained smt engine turned dynamically better execute workloads smt processor would increase performance ibm second implementation generally available hardware multithreading 2010 ibm released systems based power7 processor eight cores four simultaneous intelligent threads switches threading mode one thread two threads four threads depending number process threads scheduled time optimizes use core minimum response time maximum throughput ibm power8 8 intelligent simultaneous threads per core smt8 ibm z13 two threads per core smt-2 although many people reported sun microsystems ultrasparc t1 known niagara 14 november 2005 release defunct processor codenamed rock originally announced 2005 many delays cancelled 2009 implementations sparc focused almost entirely exploiting smt cmp techniques niagara actually using smt sun refers combined approaches cmt overall concept throughput computing niagara eight cores core one pipeline actually uses fine-grained multithreading unlike smt instructions multiple threads share issue window cycle processor uses round robin policy issue instructions next active thread cycle makes similar barrel processor sun microsystems rock processor different complex cores one pipeline oracle corporation sparc t3 eight fine-grained threads per core sparc t4 sparc t5 sparc m5 m6 m7 eight fine-grained threads per core two executed simultaneously fujitsu sparc64 vi coarse-grained vertical multithreading vmt sparc vii newer 2-way smt intel itanium montecito used coarse-grained multithreading tukwila newer use 2-way smt dual-domain multithreading intel xeon phi 4-way smt time-multiplexed multithreading hardware based threads ca n't disabled unlike regular hyperthreading intel atom released 2008 first intel product feature 2-way smt marketed hyper-threading without supporting instruction reordering speculative execution register renaming intel reintroduced hyper-threading nehalem microarchitecture absence core microarchitecture amd bulldozer microarchitecture flexfpu shared l2 cache multithreaded integer cores module single threaded partial smt implementation amd zen microarchitecture 2-way smt visc architecture uses virtual software layer translation layer dispatch single thread instructions global front end splits instructions virtual hardware threadlets dispatched separate virtual cores virtual cores send available resources physical cores multiple virtual cores push threadlets reorder buffer single physical core split partial instructions data multiple threadlets execution ports time virtual core keeps track position relative output form multithreading increase single threaded performance allowing single thread use resources cpu allocation resources dynamic near-single cycle latency level 1-4 cycles depending change allocation depending individual application needs therefore two virtual cores competing resources appropriate algorithms place determine resources allocated depending design architecture processor simultaneous multithreading decrease performance shared resources bottlenecks performance critics argue considerable burden put software developers test whether simultaneous multithreading good bad application various situations insert extra logic turn decreases performance current operating systems lack convenient api calls purpose preventing processes different priority taking resources also security concern certain simultaneous multithreading implementations intel hyperthreading netburst based processors vulnerability possible one application steal cryptographic key another application running processor monitoring cache use also sophisticated machine learning exploits ht implementation explained black hat 2018
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Computer architecture
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angelscript angelscript game-oriented interpreted compiled scripting language angelscript features static typing object handles similar c++ pointers garbage collected via reference counting object-orientation single inheritance multiple inheritance interfaces allows operators registered overloaded angelscript used c++ ide netbeans geany eclipse also supported angeljuice ide developed specifically language c c++ functions called within angelscript environment angelscript class syntax closely follows c++ classes design proxy functions required embed angelscript c++ applications easing two languages integration several differences angelscript c++ angelscript used video game development including amy dustforce gekkeiju online king arthur gold overgrowth puddle rigs rods sine mora star ruler supertuxkart warsow sven co-op jazz jackrabbit 2 plus urho3d angelscript used university ulm interactive 3d-animation program angelscript also used robotics example program behavioral rules robotic agents
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Programming language topics
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nokia n79 nokia n79 symbian os v9.3 smartphone member nokia nseries multimedia smartphone family running s60 3rd edition feature pack 2 officially announced nokia 26 august 2008 n79 advanced device 5 megapixel camera dual led flash gps many improvements nokia n78 retailed 350 euros upon release october 2008 n79 somewhat vibrant style compared usual nseries devices rotated nokia logo would later appear nokia n97 nokia advertised n79 bold-coloured xpress-on covers change software colour theme cover also slim nseries standards considered attractive features include 2.4-inch display 369 mhz arm11 processor physical keylock switch fm transmitter navi wheel 14 january 2009 nokia announced would ship sports edition dubbed n79 active included bluetooth heart rate monitor armband new version nokia sports tracker application photos music maps navigation video
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Operating systems
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call screening call screening process evaluating characteristics telephone call deciding whether answer methods may include addition us canada call screen name calling feature offered telephone companies allows customer establish list numbers anyone calling customer numbers receive automatic message indicating call accepted another name usually used marketing purposes selective call rejection also devices telezapper screening telephone calls
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Computer security
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wardriving wardriving act searching wi-fi wireless networks person usually moving vehicle using laptop smartphone software wardriving freely available internet warbiking warcycling similar wardriving done moving bicycle motorcycle practice sometimes facilitated mounting wi-fi enabled device vehicle warwalking warjogging similar wardriving done foot rather moving vehicle warrailing wartraining similar wardriving done trains tram buses means public transport wardroning accomplished drone war driving originated wardialing method popularized character played matthew broderick film wargames named film war dialing consists dialing every phone number specific sequence search modems warbiking warcycling similar wardriving done moving bicycle motorcycle practice sometimes facilitated mounting wi-fi enabled device vehicle warwalking warjogging similar wardriving done foot rather moving vehicle disadvantages method slower speed travel leading discovery infrequently discovered networks absence convenient computing environment consequently handheld devices pocket computers perform tasks users walking standing dominated practice technology advances developments early 2000s expanded extent practice advances include computers integrated wi-fi rather compactflash cf pc card pcmcia add-in cards computers dell axim compaq ipaq toshiba pocket computers starting 2002 recently active nintendo ds sony psp enthusiast communities gained wi-fi abilities devices many newer smartphones integrate wi-fi global positioning system gps warrailing wartraining similar wardriving done train tram rather slower controllable vehicle disadvantages method higher speed travel resulting less discovery infrequently discovered networks often limited major roads higher traffic warkitting combination wardriving rootkitting warkitting attack hacker replaces firmware attacked router allows control traffic victim could even permit disable tls replacing html content downloaded warkitting identified tsow jakobsson yang wardrivers use wifi-equipped device together gps device record location wireless networks results uploaded websites like wigle openbmap geomena data processed form maps network neighborhood also clients available smartphones running android upload data directly better range sensitivity antennas built bought vary omnidirectional highly directional maps known network ids used geolocation system—an alternative gps—by triangulating current position signal strengths known network ids examples include place lab intel skyhook navizon cyril houri seekerlocate seeker wireless openbmap geomena navizon openbmap combines information wi-fi cell phone tower maps contributed users wi-fi-equipped cell phones addition location finding provides navigation information allows tracking position friends geotagging december 2004 class 100 undergraduates worked map city seattle washington several weeks found 5,225 access points 44 secured wep encryption 52 open 3 pay-for-access noticed trends frequency security networks depending location many open networks clearly intended used general public network names like open share porn please free access nice information collected high-resolution maps published online previous efforts mapped cities dublin portray wardriving questionable practice typically association piggybacking though technical viewpoint everything working designed many access points broadcast identifying data accessible anyone suitable receiver could compared making map neighborhood house numbers mail box labels may claim wardriving illegal laws specifically prohibit allow wardriving though many localities laws forbidding unauthorized access computer networks protecting personal privacy google created privacy storm countries eventually admitted systematically surreptitiously gathering wifi data capturing video footage mapping data street view service since using android-based mobile devices gather data passive listen-only wardriving programs like kismet kismac communicate networks merely logging broadcast addresses likened listening radio station happens broadcasting area forms dxing types software netstumbler wardriver actively sends probe messages access point responds per design legality active wardriving less certain since wardriver temporarily becomes associated network even though data transferred access points using default box security settings intended provide wireless access request war driver liability may reduced setting computer static ip instead using dhcp preventing network granting computer ip address logging connection united states case usually referenced determining whether network accessed state v. allen case allen wardialing attempt get free long distance calling southwestern bell computer systems presented password protection screen however attempt bypass court ruled although contacted approached computer system constitute access company network also homebrew wardriving applications handheld game consoles support wi-fi sniff jazzbox/wardive nintendo ds/android road dog sony psp wifi-where iphone g-mon wardrive wigle wifi android wlanpollution symbian nokias60 devices also exists mode within sony psp wherein player able find new comrades searching wireless access points used wardrive treasure world ds commercial game gameplay wholly revolves around wardriving
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Computer security
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transport sample protocol transport sample protocol tsp open source network protocol sampling data based tcp/ip allows synchronous asynchronous sample delivery implementations linux windows solaris osf1 vxworks c java released gnu lesser general public license lgpl tsp developed use satellite validation benches
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Internet protocols
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mnos operating system mnos meaning mobilnaya operatsionnaya sistema мобильная операционная система мнос portable operating system unix-like operating system developed soviet union system derived version 6 unix consequently heavily modified incorporate many features bsd unix 1983 1986 enjoyed significant popularity ussr eastern bloc countries due light weight better performance version 7 unix later bsd unix-based alternatives development initiated ipk minavtoproma moscow 1981 development continued cooperation institutes including kurchatov institute mnos alternative demos version 1.x gradually merged 1986 1990 resulting joint os demos version 2.x mnos became first completely bilingual version unix used proprietary 8-bit cyrillic character set u-code later dropped favor koi-8 process merging demos origin version qualifier rl rabochaya loshadka working horsy
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Operating systems
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tivo media file system mfs media file system proprietary file system used tivo hard drives fault tolerant real-time recording live tv although mfs still particularly well understood programmers unaffiliated tivo corporation enough known file system able reads limited writes applications exist manipulate file system objects within applications reverse engineered software found tivo many early tivo programs little specialized scripts manipulated data mfs file system organized like database including transaction logging rollback capabilities utilizes multiple partitions drive complete system partitions come pairs one application partition media partition media region invariably quite large organized long continuous blocks data variable block size minimum least 1 megabyte designed store large sections video object tivo file system assigned id internally called fsid presumably file system id least 4 types objects mfs supports streams recordings audio video directory database files stream objects stored mfs media regions types stored application regions file system implemented entirely linux userspace primary reason tivo devised system needed way store large continuous sections data easily manner lent well streaming data directly media decoders tivo devices without cpu dependent thus cpu little involvement playback recording functionality simply directing encoder/decoder chips stream data directly drives via direct memory access mapping sections virtual memory onto drive main cpu orchestrates entire affair result data stored mfs media region formatted normal files direct data stream indexed database sections mfs application region
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Computer file systems
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common database designated areas common database designated areas cdda data bank officially designated protected areas nature reserves protected landscapes national parks etc europe data bank went live 1999 community project european environment agency eea council europe united nations environment programme world conservation monitoring centre unep-wcmc data bank divided national area international area national area member states eu eea european environment information observation network eionet data cleansing national area non-eea members international area carried unep-wcmc systems data bank follows system international union conservation nature natural resources iucn standards united nations order ensure compatibility similar data banks worldwide especially world database protected areas wdpa data bank accessed internet using website european nature information system eunis date true marine protected areas marine protected areas atlantic arc maia included data bank pursued
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Databases
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united states v. solon united states v. solon 596 f.3d 1206 10th cir 2010 case nathaniel solon casper citizen convicted possession child pornography case became known media irregularities process suspicions affirmed defendant material introduced malware computer people accused similar crimes later acquitted solon never exonerated nathaniel solon charged january 18 2007 indictment possessing child pornography october 2 2007 pleaded guilty came back another hearing january 8 2008 however solon stated innocent man reason pleaded guilty first place believed financial resources hire expert witness investigate defense regard explanation court appointed private attorney represent court approval solon able request expert witness investigation budget 20,000 supplied court
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Computer security
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penetration test penetration test colloquially known pen test pentest ethical hacking authorized simulated cyberattack computer system performed evaluate security system test performed identify weaknesses also referred vulnerabilities including potential unauthorized parties gain access system features data well strengths enabling full risk assessment completed process typically identifies target systems particular goal reviews available information undertakes various means attain goal penetration test target may white box provides background system information black box provides basic information except company name gray box penetration test combination two limited knowledge target shared auditor penetration test help determine whether system vulnerable attack defenses sufficient defenses test defeated security issues penetration test uncovers reported system owner penetration test reports may also assess potential impacts organization suggest countermeasures reduce risk national cyber security center describes penetration testing following method gaining assurance security system attempting breach system security using tools techniques adversary might goals penetration test vary depending type approved activity given engagement primary goal focused finding vulnerabilities could exploited nefarious actor informing client vulnerabilities along recommended mitigation strategies penetration tests component full security audit example payment card industry data security standard requires penetration testing regular schedule system changes flaw hypothesis methodology systems analysis penetration prediction technique list hypothesized flaws software system compiled analysis specifications documentation system list hypothesized flaws prioritized basis estimated probability flaw actually exists ease exploiting extent control compromise prioritized list used direct actual testing system mid 1960s growing popularity time-sharing computer systems made resources accessible communications lines created new security concerns scholars deborah russell g. t. gangemi sr. explain 1960s marked true beginning age computer security june 1965 example several country leading computer security experts held one first major conferences system security—hosted government contractor system development corporation sdc conference someone noted one sdc employee able easily undermine various system safeguards added sdc an/fsq-32 time-sharing computer system hopes system security study would useful attendees requested ... studies conducted areas breaking security protection time-shared system words conference participants initiated one first formal requests use computer penetration tool studying system security spring 1967 joint computer conference many leading computer specialists met discuss system security concerns conference computer security experts willis ware harold petersen rein tern rand corporation bernard peters national security agency nsa used phrase penetration describe attack computer system paper ware referred military remotely accessible time-sharing systems warning deliberate attempts penetrate computer systems must anticipated colleagues petersen turn shared concerns observing online communication systems ... vulnerable threats privacy including deliberate penetration bernard peters nsa made point insisting computer input output ... could provide large amounts information penetrating program conference computer penetration would become formally identified major threat online computer systems threat computer penetration posed next outlined major report organized united states department defense dod late 1967 essentially dod officials turned willis ware lead task force experts nsa cia dod academia industry formally assess security time-sharing computer systems relying many papers presented spring 1967 joint computer conference task force largely confirmed threat system security computer penetration posed ware report initially classified many country leading computer experts quickly identified study definitive document computer security jeffrey r. yost charles babbage institute recently described ware report ... far important thorough study technical operational issues regarding secure computing systems time period effect ware report reaffirmed major threat posed computer penetration new online time-sharing computer systems better understand system weaknesses federal government contractors soon began organizing teams penetrators known tiger teams use computer penetration test system security deborah russell g. t. gangemi sr. stated 1970s ... 'tiger teams first emerged computer scene tiger teams government industry-sponsored teams crackers attempted break defenses computer systems effort uncover eventually patch security holes leading scholar history computer security donald mackenzie similarly points rand done penetration studies experiments circumventing computer security controls early time-sharing systems behalf government jeffrey r. yost charles babbage institute work history computer security also acknowledges rand corporation sdc engaged first so-called 'penetration studies try infiltrate time-sharing systems order test vulnerability virtually early studies tiger teams successfully broke targeted computer systems country time-sharing systems poor defenses early tiger team actions efforts rand corporation demonstrated usefulness penetration tool assessing system security time one rand analyst noted tests ... demonstrated practicality system-penetration tool evaluating effectiveness adequacy implemented data security safeguards addition number rand analysts insisted penetration test exercises offered several benefits justified continued use noted one paper penetrator seems develop diabolical frame mind search operating system weaknesses incompleteness difficult emulate reasons others many analysts rand recommended continued study penetration techniques usefulness assessing system security perhaps leading computer penetration expert formative years james p. anderson worked nsa rand government agencies study system security early 1971 u.s. air force contracted anderson private company study security time-sharing system pentagon study anderson outlined number major factors involved computer penetration anderson described general attack sequence steps time anderson description general computer penetration steps helped guide many security experts relied technique assess time-sharing computer system security following years computer penetration tool security assessment became refined sophisticated early 1980s journalist william broad briefly summarized ongoing efforts tiger teams assess system security broad reported dod-sponsored report willis ware ... showed spies could actively penetrate computers steal copy electronic files subvert devices normally guard top-secret information study touched decade quiet activity elite groups computer scientists working government tried break sensitive computers succeeded every attempt various studies may suggested computer security u.s. remained major problem scholar edward hunt recently made broader point extensive study computer penetration security tool hunt suggests recent paper history penetration testing defense establishment ultimately ... created many tools used modern day cyberwarfare carefully defined researched many ways computer penetrators could hack targeted systems wide variety security assessment tools available assist penetration testing including free-of-charge free software commercial software several operating system distributions geared towards penetration testing distributions typically contain pre-packaged pre-configured set tools penetration tester hunt individual tool might increase risk complications—such compile errors dependency issues configuration errors also acquiring additional tools may practical tester context notable penetration testing os examples include many specialized operating systems facilitate penetration testing—each less dedicated specific field penetration testing number linux distributions include known os application vulnerabilities deployed targets practice systems help new security professionals try latest security tools lab environment examples include damn vulnerable linux dvl owasp web testing environment wtw metasploitable process penetration testing may simplified five phases attacker exploited one vulnerability may gain access machines process repeats i.e look new vulnerabilities attempt exploit process referred pivoting legal operations let tester execute illegal operation include unescaped sql commands unchanged hashed passwords source-visible projects human relationships old hashing cryptographic functions single flaw may enough enable critically serious exploit leveraging multiple known flaws shaping payload way appears valid operation almost always required metasploit provides ruby library common tasks maintains database known exploits budget time constraints fuzzing common technique discovers vulnerabilities aims get unhandled error random input tester uses random input access less often used code paths well-trodden code paths usually free errors errors useful either expose information http server crashes full info trace-backs—or directly usable buffer overflows imagine website 100 text input boxes vulnerable sql injections certain strings submitting random strings boxes hopefully hits bugged code path error shows broken html page half rendered sql error case text boxes treated input streams however software systems many possible input streams cookie session data uploaded file stream rpc channels memory errors happen input streams test goal first get unhandled error understand flaw based failed test case testers write automated tool test understanding flaw correct may become obvious package payload target system triggers execution viable one hope another error produced fuzzer yields fruit use fuzzer saves time checking adequate code paths exploits unlikely illegal operation payload metasploit terminology include functions logging keystrokes taking screenshots installing adware stealing credentials creating backdoors using shellcode altering data companies maintain large databases known exploits provide products automatically test target systems vulnerabilities general services administration gsa standardized penetration test service pre-vetted support service rapidly address potential vulnerabilities stop adversaries impact us federal state local governments services commonly referred highly adaptive cybersecurity services hacs listed us gsa advantage website effort identified key service providers technically reviewed vetted provide advanced penetration services gsa service intended improve rapid ordering deployment services reduce us government contract duplication protect support us infrastructure timely efficient manner 132-45a penetration testing security testing service assessors mimic real-world attacks identify methods circumventing security features application system network hacs penetration testing services typically strategically test effectiveness organization preventive detective security measures employed protect assets data part service certified ethical hackers typically conduct simulated attack system systems applications another target environment searching security weaknesses testing typically document vulnerabilities outline defenses effective defeated exploited also typically provide recommended remediation plans address weaknesses discovered uk penetration testing services standardized via professional bodies working collaboration national cyber security centre
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Computer security
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disk encryption theory disk encryption special case data rest protection storage medium sector-addressable device e.g. hard disk article presents cryptographic aspects problem discussion different software packages hardware devices devoted problem see disk encryption software disk encryption hardware disk encryption methods aim provide three distinct properties first property requires defining adversary data kept confidential strongest adversaries studied field disk encryption abilities method provides good confidentiality information adversary determine time whether data sector changed since last time looked second property requires dividing disk several sectors usually 512 bytes bits long encrypted decrypted independently turn data stay confidential encryption method must tweakable two sectors processed exactly way otherwise adversary could decrypt sector disk copying unused sector disk requesting decryption third property generally non-controversial however indirectly prohibits use stream ciphers since stream ciphers require security initial state used twice would case sector updated different data thus would require encryption method store separate initial states every sector disk—seemingly waste space alternative block cipher limited certain block size usually 128 256 bits disk encryption chiefly studies chaining modes expand encryption block length cover whole disk sector considerations already listed make several well-known chaining modes unsuitable ecb mode tweaked modes turn block ciphers stream ciphers ctr mode three properties provide assurance disk integrity n't tell whether adversary modifying ciphertext part absolute assurance disk integrity impossible matter adversary could always revert entire disk prior state circumventing checks non-absolute level disk integrity desired achieved within encrypted disk file-by-file basis using message authentication codes like encryption schemes block cipher-based disk encryption makes use modes operation allow encrypting larger amounts data ciphers block-size typically 128 bits modes therefore rules repeatedly apply ciphers single-block operations cipher-block chaining cbc common chaining mode previous block ciphertext xored current block plaintext encryption since n't previous block ciphertext first block initialization vector iv must used formula_2 turn makes cbc tweakable ways cbc suffers problems example ivs predictable adversary may leave watermark disk i.e. store specially created file combination files identifiable even encryption exact method constructing watermark depends exact function providing ivs general recipe create two encrypted sectors identical first blocks formula_3 formula_4 two related formula_5 thus encryption formula_6 identical encryption formula_7 leaving watermark disk exact pattern same-different-same-different disk altered make watermark unique given file protect watermarking attack cipher hash function used generate ivs key current sector number adversary predict ivs particular essiv approach uses block cipher ctr mode generate ivs essiv method generating initialization vectors block encryption use disk encryption usual methods generating ivs predictable sequences numbers based example time stamp sector number prevents certain attacks watermarking attack essiv prevents attacks generating ivs combination sector number sn hash key combination key form hash makes iv unpredictable essiv designed clemens fruhwirth integrated linux kernel since version 2.6.10 though similar scheme used generate ivs openbsd swap encryption since 2000 essiv supported option dm-crypt freeotfe disk encryption systems cbc without essiv ensures confidentiality ensure integrity encrypted data plaintext known adversary possible change every second plaintext block value chosen attacker blocks changed random values used practical attacks disk encryption cbc cbc-essiv mode order prevent elaborate attacks different modes operation introduced tweakable narrow-block encryption lrw xex wide-block encryption cmc eme whereas purpose usual block cipher formula_9 mimic random permutation secret key formula_10 purpose tweakable encryption formula_11is mimic random permutation secret key formula_10 known tweak formula_13 tweakable narrow-block encryption lrw instantiation mode operations introduced liskov rivest wagner see theorem 2 mode uses two keys formula_10 key block cipher formula_15 additional key size block example aes 256-bit key formula_10 256-bit number formula_15 128-bit number encrypting block formula_18 logical index tweak formula_19 uses following formula multiplication formula_21 addition formula_22 performed finite field formula_23 aes precomputation single multiplication per sector required note addition binary finite field simple bitwise addition also known xor formula_24 formula_25 precomputed possible values formula_26 mode operation needs single encryption per block protects attacks except minor leak user changes single plaintext block sector single ciphertext block changes note leak ecb mode lrw mode equal plaintexts different positions encrypted different ciphertexts security concerns exist lrw mode operation replaced xts lrw employed bestcrypt supported option dm-crypt freeotfe disk encryption systems another tweakable encryption mode xex xor–encrypt–xor designed rogaway allow efficient processing consecutive blocks respect cipher used within one data unit e.g. disk sector tweak represented combination sector address index block within sector original xex mode proposed rogaway allows several indices ciphertext formula_27 obtained using basic operations lrw mode aes cipher galois field multiplication ones used galois/counter mode gcm thus permitting compact implementation universal lrw/xex/gcm hardware ciphertext stealing provides support sectors size divisible block size example 520-byte sectors 16-byte blocks xts-aes standardized 2007-12-19 ieee p1619 standard supports using different key iv encryption block encryption contrary intent xex seems rooted misinterpretation original xex paper harm security result users wanting aes-256 aes-128 encryption must supply 512 bits 256 bits key respectively january 27 2010 nist released special publication sp 800-38e final form sp 800-38e recommendation xts-aes mode operation standardized ieee std 1619-2007 cryptographic modules publication approves xts-aes mode aes algorithm reference ieee std 1619-2007 subject one additional requirement limits maximum size encrypted data unit typically sector disk block formula_35 aes blocks according sp 800-38e absence authentication access control xts-aes provides protection approved confidentiality-only modes unauthorized manipulation encrypted data xts supported bestcrypt botan netbsd cgd dm-crypt freeotfe truecrypt veracrypt diskcryptor freebsd geli openbsd softraid disk encryption software openssl mac os x lion filevault 2 windows 10 bitlocker wolfcrypt xts mode susceptible data manipulation tampering applications must employ measures detect modifications data manipulation tampering concern ... since authentication tags ciphertext original modified attacker decrypted plaintext built-in mechanism detect alterations best done ensure alteration ciphertext completely randomize plaintext rely application uses transform include sufficient redundancy plaintext detect discard random plaintexts would require maintaining checksums data metadata disk done zfs btrfs however commonly used file systems ext4 ntfs metadata protected tampering detection data tampering non-existent mode susceptible traffic analysis replay randomization attacks sectors 16-byte blocks given sector rewritten attackers collect fine-grained 16 byte ciphertexts used analysis replay attacks 16-byte granularity would possible define sector-wide block ciphers unfortunately degraded performance see cmc eme protect even minor leak mentioned lrw unfortunately price twofold degradation performance block must encrypted twice many consider high cost since leak sector level unavoidable anyway cmc introduced halevi rogaway stands cbc–mask–cbc whole sector encrypted cbc mode formula_36 ciphertext masked xoring formula_37 re-encrypted cbc mode starting last block underlying block cipher strong pseudorandom permutation prp sector level scheme tweakable prp one problem order decrypt formula_38 one must sequentially pass data twice order solve problem halevi rogaway introduced parallelizable variant called eme ecb–mask–ecb works following way note unlike lrw cmc single key formula_10 cmc eme considered standardization siswg eme patented favored primary supported mode authenticated encryption scheme iapm provides encryption well authentication tag encryption component iapm mode completely describes lrw xex schemes hence xts without ciphertext stealing aspect described detail figures 8 5 us patent 6,963,976
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Computer file systems
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magnus sahlgren magnus sahlgren born january 1 1973 swedish computational linguist guitarist magnus sahlgren known work random indexing applied distributional semantics published research projects swedish institute computer science later gavagai ab research company co-founded 2008 sahlgren dissertation word-space model awarded prize prominent scholarly achievement 2006 stockholm university faculty humanities sahlgren lead guitarist metal band lake tears name associated 2009 also played dismember 1998 2003 tiamat recording acclaimed wildhoney album 1994 helped band achieve technical proficiency helping songwriting solos session artist 2004 accepted full-time member lake tears since influences even visible notably album moons mushrooms performs solos every track
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Computational linguistics
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validation authority public key infrastructure validation authority va entity provides service used verify validity digital certificate per mechanisms described x.509 standard page 69 dominant method used purpose host certificate revocation list download via http ldap protocols reduce amount network traffic required certificate validation ocsp protocol may used instead validation authority capable responding network-based request crl lacks ability issue revoke certificates must continuously updated current crl information certificate authority issued certificates contained within crl potentially labor-intensive process use dedicated validation authority allows dynamic validation certificates issued offline root certificate authority root ca unavailable network traffic certificates issued always verified via validation authority protocols mentioned ongoing administrative overhead maintaining crls hosted validation authority typically minimal uncommon root cas issue revoke large numbers certificates
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Computer security
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freifunk freifunk german free radio non-commercial open grassroots initiative support free computer networks german region freifunk part international movement wireless community network initiative counts 400 local communities 41,000 access points among münster aachen munich stuttgart paderborn biggest communities 1000 access points main goals freifunk build large scale free wireless wi-fi network decentralized owned run support local communication initiative based picopeering agreement agreement participants agree upon network free discrimination sense net neutrality similar grassroots initiatives austria switzerland funkfeuer openwireless like many free community-driven networks freifunk uses mesh technology bring ad hoc networks interconnecting multiple wireless lans wi-fi mobile ad hoc network routers connect using special routing software router fails software automatically calculates new route destination software freifunk firmware based openwrt free software several different implementations firmware depending hardware protocols local communities use first wi-fi ad hoc network done georgia usa 1999 demonstrated toh.it six-node implementation running associativity-based routing protocol linux kernel wavelan wifi abr patented protocol following experience freifunk work standard ietf protocols two common standard proposals olsr b.a.t.m.a.n development b.a.t.m.a.n driven freifunk activists volunteering basis one results berlon workshop october 2002 free wireless community networks berlin london picopeering agreement agreement rationales free networks describes transmission people data handled free network become core agreement community workshop participants also agreed upon regular meetings berlin build free wifi network ever since weekly meetings c-base hackerspace every wednesday time german language site freifunk.net started september 2003 freifunk activists founded non-profit association förderverein freie netzwerke e.v support free communication infrastructures following years initiative became quite successful germany also became easier install freifunk firmware off-the-shelf wireless routers yearly wireless community weekend taking place berlin c-base 2012 berlin freifunk community got lot media attention project called freifunk freedom fighter box project fights secondary liability secondary liability legal situation makes owners open non-encrypted wireless access points liable users internet connection outlined störerhaftung law owners thus forced pay copyright infringements third persons opened network public legal practice led fear uncertainty made many people close access points e.g cafés public locations freifunk freedom fighter box preconfigured access point sent data public network sweden vpn connection sweden countries secondary liability 2013 hamburg freifunk community set network 300 nodes using vpn tunnels netherlands many new freifunk communities emerged berlin community building backbone network based microwave transmission longer distances project funded local broadcasting corporation medienanstalt berlin-brandenburg still on-going germany
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Distributed computing architecture
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apache kylin apache kylin open source distributed analytics engine designed provide sql interface multi-dimensional analysis olap hadoop alluxio supporting extremely large datasets originally developed ebay project apache software foundation kylin project started 2013 ebay r shanghai china oct 2014 kylin v0.6 open sourced github.com name kylinolap nov 2014 kylin joined apache software foundation incubator december 2015 apache kylin graduated top level project kyligence inc chinese company provides commercial support apache kylin consists primarily original developers open source code apache kylin built top apache hadoop apache hive apache hbase apache calcite apache spark technologies technologies powerful matured making kylin able support massive data load easily scale kylin following core components apache kylin adopted many companies olap platform production typical users includes ebay meituan xiaomi netease beike yahoo japan apache kylin roadmap kylin website
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Databases
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mips architecture mips microprocessor without interlocked pipelined stages reduced instruction set computer risc instruction set architecture isa developed mips computer systems mips technologies based united states multiple versions mips including mips ii iii iv v well five releases mips32/64 32- 64-bit implementations respectively early mips architectures 32-bit 64-bit versions developed later april 2017 current version mips mips32/64 release 6 mips32/64 primarily differs mips i–v defining privileged kernel mode system control coprocessor addition user mode architecture computer architecture courses universities technical schools often study mips architecture architecture greatly influenced later risc architectures alpha april 2017 mips processors used embedded systems residential gateways routers originally mips designed general-purpose computing 1980s 1990s mips processors personal workstation server computers used many companies digital equipment corporation mips computer systems nec pyramid technology sicortex siemens nixdorf silicon graphics tandem computers historically video game consoles nintendo 64 sony playstation playstation 2 playstation portable used mips processors mips processors also used popular supercomputers 1990s systems dropped top500 list uses complemented embedded applications first 1990s mips became major presence embedded processor market 2000s mips processors applications mid- late-1990s estimated one three risc microprocessors produced mips processor mips modular architecture supporting four coprocessors cp0/1/2/3 mips terminology cp0 system control coprocessor essential part processor implementation-defined mips i–v cp1 optional floating-point unit fpu cp2/3 optional implementation-defined coprocessors mips iii removed cp3 reused opcodes purposes example playstation video game console cp2 geometry transformation engine gte accelerates processing geometry 3d computer graphics mips architecture several optional extensions mips-3d simple set floating-point simd instructions dedicated common 3d tasks mdmx madmax extensive integer simd instruction set using 64-bit floating-point registers mips16e adds compression instruction stream make programs take less room mips mt adds multithreading capability december 2018 wave computing new owner mips architecture see mips technologies announced mips isa open-sourced program dubbed mips open initiative program planned 2019 intended open access recent versions 32-bit 64-bit designs making available without licensing royalty fees well granting participants licenses existing mips patents first version mips architecture designed mips computer systems r2000 microprocessor first mips implementation mips r2000 introduced together 1985 mips ii introduced mips renamed mips distinguish new version mips load/store architecture also known register-register architecture except load/store instructions used access memory instructions operate registers mips thirty-two 32-bit general-purpose registers gpr register 0 hardwired zero writes discarded register 31 link register integer multiplication division instructions run asynchronously instructions pair 32-bit registers hi lo provided small set instructions copying data general-purpose registers hi/lo registers program counter 32 bits two low-order bits always contain zero since mips instructions 32 bits long aligned natural word boundaries instructions divided three types r j every instruction starts 6-bit opcode addition opcode r-type instructions specify three registers shift amount field function field i-type instructions specify two registers 16-bit immediate value j-type instructions follow opcode 26-bit jump target following three formats used core instruction set mips instructions load store 8-bit bytes 16-bit halfwords 32-bit words one addressing mode supported base displacement since mips 32-bit architecture loading quantities fewer 32 bits requires datum either signed- zero-extended 32 bits load instructions suffixed unsigned perform zero extension otherwise sign extension performed load instructions source base contents gpr rs write result another gpr rt store instructions source base contents gpr rs store data another gpr rt load store instructions compute memory address summing base sign-extended 16-bit immediate mips requires memory accesses aligned natural word boundaries otherwise exception signaled support efficient unaligned memory accesses load/store word instructions suffixed left right load instructions followed load delay slot instruction load delay slot use data loaded load instruction load delay slot filled instruction dependent load nop substituted instruction found mips instructions perform addition subtraction instructions source operands two gprs rs rt write result third gpr rd alternatively addition source one operands 16-bit immediate sign-extended 32 bits instructions addition subtraction two variants default exception signaled result overflows instructions unsigned suffix signal exception overflow check interprets result 32-bit two complement integer mips instructions perform bitwise logical xor instructions source operands two gprs write result third gpr xor instructions alternatively source one operands 16-bit immediate zero-extended 32 bits set relation instructions write one zero destination register specified relation true false instructions source operands two gprs one gpr 16-bit immediate sign-extended 32 bits write result third gpr default operands interpreted signed integers variants instructions suffixed unsigned interpret operands unsigned integers even source operand sign-extended 16-bit immediate load immediate upper instruction copies 16-bit immediate high-order 16 bits gpr used conjunction immediate instruction load 32-bit immediate register mips instructions perform left right logical shifts right arithmetic shifts operand obtained gpr rt result written another gpr rd shift distance obtained either gpr rs 5-bit shift amount sa field mips instructions signed unsigned integer multiplication division instructions source operands two gprs write results pair 32-bit registers called hi lo since may execute separately concurrently cpu instructions multiplication high- low-order halves 64-bit product written hi lo respectively division quotient written lo remainder hi access results pair instructions move hi move lo provided copy contents hi lo gpr instructions interlocked reads hi lo proceed past unfinished arithmetic instruction write hi lo another pair instructions move hi move lo copies contents gpr hi lo instructions used restore hi lo original state exception handling instructions read hi lo must separated two instructions write hi lo mips control flow instructions followed branch delay slot unless branch delay slot filled instruction performing useful work nop substituted mips branch instructions compare contents gpr rs zero another gpr rt signed integers branch specified condition true control transferred address computed shifting 16-bit offset left two bits sign-extending 18-bit result adding 32-bit sign-extended result sum program counter instruction address 8 jumps two versions absolute register-indirect absolute jumps jump jump link compute address control transferred shifting 26-bit instr_index left two bits concatenating 28-bit result four high-order bits address instruction branch delay slot register-indirect jumps transfer control instruction address sourced gpr rs address sourced gpr must word-aligned else exception signaled instruction branch delay slot executed branch jump instructions link except jump link register save return address gpr 31 jump link register instruction permits return address saved writable gpr mips two instructions software signal exception system call breakpoint system call used user mode software make kernel calls breakpoint used transfer control debugger via kernel exception handler instructions 20-bit code field contain operating environment-specific information exception handler mips 32 floating-point registers two registers paired double precision numbers odd numbered registers used arithmetic branching part double precision register pair resulting 16 usable registers instructions moves/copies loads/stores affected single precision denoted .s suffix double precision denoted .d suffix mips ii removed load delay slot added several sets instructions shared-memory multiprocessing synchronize shared memory load linked word store conditional word instructions added set trap-on-condition instructions added instructions caused exception evaluated condition true existing branch instructions given branch-likely versions executed instruction branch delay slot branch taken instructions improve performance certain cases allowing useful instructions fill branch delay slot doubleword load store instructions cop1–3 added consistent memory access instructions loads stores required doubleword naturally aligned instruction set floating point coprocessor also several instructions added ieee 754-compliant floating-point square root instruction added supported single- double-precision operands set instructions converted single- double-precision floating-point numbers 32-bit words added complemented existing conversion instructions allowing ieee rounding mode specified instruction instead floating point control status register mips computer systems r6000 microprocessor 1989 first mips ii implementation designed servers r6000 fabricated sold bipolar integrated technology commercial failure mid-1990s many new 32-bit mips processors embedded systems mips ii implementations introduction 64-bit mips iii architecture 1991 left mips ii newest 32-bit mips architecture mips32 introduced 1999.a mips iii backwards-compatible extension mips ii added support 64-bit memory addressing integer operations 64-bit data type called doubleword mips iii extended general-purpose registers hi/lo registers program counter 64 bits support new instructions added load store doublewords perform integer addition subtraction multiplication division shift operations move doubleword gprs hi/lo registers existing instructions originally defined operate 32-bit words redefined necessary sign-extend 32-bit results permit words doublewords treated identically instructions among instructions redefined load word mips iii sign-extends words 64 bits complement load word version zero-extends added r instruction format inability specify full shift distance 64-bit shifts 5-bit shift amount field narrow specify shift distance doublewords required mips iii provide three 64-bit versions mips shift instruction first version 64-bit version original shift instructions used specify constant shift distances 0–31 bits second version similar first adds 32 shift amount field value constant shift distances 32–64 bits specified third version obtains shift distance six low-order bits gpr mips iii added supervisor privilege level existing kernel user privilege levels feature affected implementation-defined system control processor coprocessor 0 mips iii removed coprocessor 3 cp3 support instructions reused opcodes new doubleword instructions remaining coprocessors gained instructions move doublewords coprocessor registers gprs floating general registers fgrs extended 64 bits requirement instructions use even-numbered register removed incompatible earlier versions architecture bit floating-point control/status register used operate mips iii floating-point unit fpu mips i- ii-compatible mode floating-point control registers extended compatibility new floating-point instructions added copy doublewords cpu fpu convert single- double-precision floating-point numbers doubleword integers vice versa mips computer systems r4000 microprocessor 1991 first mips iii implementation designed use personal workstation server computers mips computer systems aggressively promoted mips architecture r4000 establishing advanced computing environment ace consortium advance advanced risc computing arc standard aimed establish mips dominant personal computing platform arc found little success personal computers r4000 r4400 derivative widely used workstation server computers especially largest user silicon graphics uses r4000 included high-end embedded systems supercomputers mips iii eventually implemented number embedded microprocessors quantum effect design r4600 1993 derivatives widely used high-end embedded systems low-end workstations servers mips technologies r4200 1994 designed embedded systems laptop personal computers derivative r4300i fabricated nec electronics used nintendo 64 game console nintendo 64 along playstation among highest volume users mips architecture processors mid-1990s mips iv fourth version architecture superset mips iii compatible existing versions mips mips iv designed mainly improve floating-point fp performance improve access operands indexed addressing mode base index sourced gprs fp loads stores added prefetch instructions performing memory prefetching specifying cache hints supported base offset base index addressing modes mips iv added several features improve instruction-level parallelism alleviate bottleneck caused single condition bit seven condition code bits added floating-point control status register bringing total eight fp comparison branch instructions redefined could specify condition bit written read respectively delay slot fp branch read condition bit written prior fp comparison removed support partial predication added form conditional move instructions gprs fprs implementation could choose precise imprecise exceptions ieee 754 traps mips iv added several new fp arithmetic instructions single- double-precision fpns fused-multiply add subtract reciprocal reciprocal square-root fp fused-multiply add subtract instructions perform either one two roundings implementation-defined exceed meet ieee 754 accuracy requirements respectively fp reciprocal reciprocal square-root instructions comply ieee 754 accuracy requirements produce results differ required accuracy one two units last place implementation defined instructions serve applications instruction latency important accuracy first mips iv implementation mips technologies r8000 microprocessor chipset 1994 design r8000 began silicon graphics inc. used high-end workstations servers scientific technical applications high performance large floating-point workloads important later implementations mips technologies r10000 1996 quantum effect devices r5000 1996 rm7000 1998 r10000 fabricated sold nec electronics toshiba derivatives used nec pyramid technology silicon graphics inc. tandem computers among others workstations servers supercomputers r5000 r7000 found use high-end embedded systems personal computers low-end workstations servers derivative r5000 toshiba r5900 used sony computer entertainment emotion engine powered playstation 2 game console announced october 21 1996 microprocessor forum 1996 alongside mips digital media extensions mdmx extension mips v designed improve performance 3d graphics transformations mid-1990s major use non-embedded mips microprocessors graphics workstations sgi mips v completed integer-only mdmx extension provide complete system improving performance 3d graphics applications mips v implementations never introduced may 12 1997 sgi announced h1 beast h2 capitan microprocessors former first mips v implementation due introduced first half 1999 h1 h2 projects later combined eventually canceled 1998 mips v implementations mips64 release 1 1999 based mips v retains features optional coprocessor 1 fpu feature called paired-single mips v added new data type paired single ps consisted two single-precision 32-bit floating-point numbers stored existing 64-bit floating-point registers variants existing floating-point instructions arithmetic compare conditional move added operate data type simd fashion new instructions added loading rearranging converting ps data first instruction set exploit floating-point simd existing resources mips technologies spun-out silicon graphics 1998 refocused embedded market mips v successive version strict superset previous version property found problem architecture definition changed define 32-bit 64-bit architecture mips32 mips64 introduced 1999 mips32 based mips ii additional features mips iii mips iv mips v mips64 based mips v. nec toshiba sibyte later acquired broadcom obtained licenses mips64 soon announced philips lsi logic idt raza microelectronics inc. cavium loongson technology ingenic semiconductor since joined first release mips32 based mips ii added conditional moves prefetch instructions features r4000 r5000 families 64-bit processors first release mips64 adds mips32 mode run 32-bit code mul madd multiply-add instructions previously available implementations added mips32 mips64 specifications cache control instructions announced december 6 2012 release 4 skipped number four perceived unlucky many asian cultures mips32/mips64 release 6 2014 added following removed infrequently used instructions reorganized instruction encoding freeing space future expansions micromips32/64 architectures supersets mips32 mips64 architectures respectively designed replace mips16e ase disadvantage mips16e requires mode switch 16-bit instructions processed micromips adds versions most-frequently used 32-bit instructions encoded 16-bit instructions allows programs intermix 16- 32-bit instructions without switch modes micromips introduced alongside mips32/64 release 3 subsequent release mips32/64 corresponding micromips32/64 version processor may implement micromips32/64 micromips32/64 corresponding mips32/64 subset starting mips32/64 release 6 support mips16e ended micromips form code compression mips base mips32 mips64 architectures supplemented number optional architectural extensions collectively referred application-specific extensions ases ases provide features improve efficiency performance certain workloads digital signal processing enhancements microcontroller applications mcu ase application-specific extension developed extend interrupt controller support reduce interrupt latency enhance i/o peripheral control function typically required microcontroller system designs mips16 application-specific extension mips v designed lsi logic mips technologies announced october 21 1996 alongside first implementation lsi logic tinyrisc processor mips16 subsequently licensed nec electronics philips semiconductors toshiba among others implemented extension mips ii iii architectures mips16 decreases size application 40 using 16-bit instructions instead 32-bit instructions also improves power efficiency instruction cache hit rate equivalent performance base architecture supported hardware software development tools mips technologies providers mips16e improved version mips16 first supported mips32 mips64 release 1 mips16e2 improved version mips16 supported mips32 mips64 release 5 release 6 replaced micromips dsp ase optional extension mips32/mips64 release 2 newer instruction sets used accelerate large range media computations—particularly audio video dsp module comprises set instructions state integer pipeline requires minimal additional logic implement mips processor cores revision 2 ase introduced second half 2006 revision adds extra instructions original ase otherwise backwards-compatible unlike bulk mips architecture fairly irregular set operations many chosen particular relevance key algorithm main novel features vs original mips32 make use mips dsp ase may linux 2.6.12-rc5 starting 2005-05-31 adds support dsp ase note actually make use dsp ase toolchain support required gcc already support dsp dspr2 instruction set extensions designed accelerate multimedia hardware supported virtualization technology multi-threaded mips core support two vpes virtual processing elements share single pipeline well hardware resources however since vpe includes complete copy processor state seen software system vpe appears complete standalone processor smp linux operating system fine-grained thread processing applications vpe capable supporting nine tcs allocated across two vpes tcs share common execution unit program counter core register files handle thread software mips mt architecture also allows allocation processor cycles threads sets relative thread priorities optional quality service qos manager block enables two prioritization mechanisms determine flow information across bus first mechanism allows user prioritize one thread another second mechanism used allocate specified ratio cycles specific threads time combined use mechanisms allows effective allocation bandwidth set threads better control latencies real-time systems system-level determinism critical qos block facilitates improvement predictability system hardware designers advanced systems may replace standard qos block provided mips technologies one specifically tuned application single-threaded microprocessors today waste many cycles waiting access memory considerably limiting system performance use multi-threading masks effect memory latency increasing processor utilization one thread stalls additional threads instantly fed pipeline executed resulting significant gain application throughput users allocate dedicated processing bandwidth real-time tasks resulting guaranteed quality service qos mips ’ mt technology constantly monitors progress threads dynamically takes corrective actions meet exceed real-time requirements processor pipeline achieve 80-90 utilization switching threads data-dependent stalls cache misses leads improved mobile device user experience responsiveness greatly increased smartmips application-specific extension ase designed gemplus international mips technologies improve performance reduce memory consumption smart card software supported mips32 since smart cards require capabilities mips64 processors smart cards use smartmips open virtual platforms ovp includes freely available non-commercial use simulator ovpsim library models processors peripherals platforms apis enable users develop models models library open source written c include mips 4k 24k 34k 74k 1004k 1074k m14k microaptiv interaptiv proaptiv 32-bit cores mips 64-bit 5k range cores models created maintained imperas partnership mips technologies tested assigned mips-verified tm mark sample mips-based platforms include bare metal environments platforms booting unmodified linux binary images platforms–emulators available source binaries fast free non-commercial usage easy use ovpsim developed maintained imperas fast hundreds million instructions per second built handle multicore homogeneous heterogeneous architectures systems freely available mips32 simulator earlier versions simulated r2000/r3000 called spim use education edumips64 gpl graphical cross-platform mips64 cpu simulator written java/swing supports wide subset mips64 isa allows user graphically see happens pipeline assembly program run cpu mars another gui-based mips emulator designed use education specifically use hennessy computer organization design webmips browser-based mips simulator visual representation generic pipelined processor simulator quite useful register tracking step step execution advanced free emulators available gxemul formerly known mips64emul project qemu projects emulate various mips iii iv microprocessors addition entire computer systems use commercial simulators available especially embedded use mips processors example wind river simics mips 4kc 5kc pmc rm9000 qed rm7000 broadcom/netlogic ec4400 cavium octeon imperas mips32 mips64 cores vast systems r3000 r4000 coware mips4ke mips24k mips25kf mips34k wepsim browser-based simulator subset mips instructions micro-programmed simulator useful order learn cpu works microprogramming mips routines traps interruptions system calls etc
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Computer architecture
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stm32 stm32 family 32-bit microcontroller integrated circuits stmicroelectronics stm32 chips grouped related series based around 32-bit arm processor core cortex-m33f cortex-m7f cortex-m4f cortex-m3 cortex-m0+ cortex-m0 internally microcontroller consists processor core static ram flash memory debugging interface various peripherals stm32 family microcontroller ics based 32-bit risc arm cortex-m33f cortex-m7f cortex-m4f cortex-m3 cortex-m0+ cortex-m0 cores stmicroelectronics licenses arm processor ip arm holdings arm core designs numerous configurable options st chooses individual configuration use design st attaches peripherals core converting design silicon die following tables summarize stm32 microcontroller families stm32 third arm family stmicroelectronics follows earlier str9 family based arm9e core str7 family based arm7tdmi core following history stm32 family evolved stm32 family consists ten series microcontrollers h7 f7 f4 f3 f2 f1 f0 l4 l1 l0 stm32 microcontroller series based upon either cortex-m7f cortex-m4f cortex-m3 cortex-m0+ cortex-m0 arm processor core cortex-m4f conceptually cortex-m3 plus dsp single-precision floating point instructions stm32 h7-series group stm32 microcontrollers based arm cortex-m7f core stm32 f7-series group stm32 microcontrollers based arm cortex-m7f core many f7 series pin-to-pin compatible stm32 f4-series core stm32 f4-series first group stm32 microcontrollers based arm cortex-m4f core f4-series also first stm32 series dsp floating point instructions f4 pin-to-pin compatible stm32 f2-series adds higher clock speed 64 kb ccm static ram full duplex i²s improved real-time clock faster adcs summary series stm32 f3-series second group stm32 microcontrollers based arm cortex-m4f core f3 almost pin-to-pin compatible stm32 f1-series summary series distinguishing feature series presence four fast 12-bit simultaneous sampling adcs multiplexer 30 channels four matched 8 mhz bandwidth op-amps pins exposed additionally internal pga programmable gain array network exposed pads allow range analog signal conditioning circuits like band-pass filters anti-alias filters charge amplifiers integrators/differentiators 'instrumentation high-gain differential inputs eliminates need external op-amps many applications built-in two-channel dac arbitrary waveform well hardware-generated waveform sine triangle noise etc capability analog devices completely independent partially internally connected meaning one nearly everything needed advanced measurement sensor interfacing system single chip four adcs simultaneously sampled making wide range precision analog control equipment possible also possible use hardware scheduler multiplexer array allowing good timing accuracy sampling 4 channels independent main processor thread sampling multiplexing trigger controlled variety sources including timers built-in comparators allowing irregular sampling intervals needed op-amps inputs feature 2-to-1 analog multiplexer allowing total eight analog channels pre-processed using op-amp op-amp outputs internally connected adcs stm32 f2-series stm32 microcontrollers based arm cortex-m3 core recent fastest cortex-m3 series f2 pin-to-pin compatible stm32 f4-series summary series stm32 f1-series first group stm32 microcontrollers based arm cortex-m3 core considered mainstream arm microcontrollers f1-series evolved time increasing cpu speed size internal memory variety peripherals five f1 lines connectivity stm32f105/107 performance stm32f103 usb access stm32f102 access stm32f101 value stm32f100 summary series stm32 f0-series first group arm cortex-m0 chips stm32 family summary series stm32 g0-series lower power alternative l0 series stm32 l5-series evolution stm32l-series ultra-low power microcontrollers stm32 l4-series evolution stm32l1-series ultra-low power microcontrollers example l4 mcu stm32l432kc ufqfpn32 package stm32 l1-series first group stm32 microcontrollers primary goal ultra-low power usage battery-powered applications summary series stm32 l0-series first group stm32 microcontrollers based arm cortex-m0+ core series targets low power applications summary series stm32 w-series arm chips primary feature targeting rf communication applications summary series stmicroelectronics provides selection stm32 microcontrollers ready used java programming language special series embeds required features execute java programs based existing stm32 f1 f2 f4 f0 l0 families two sets special part numbers enabled java production part numbers end letter j sample part numbers end letter u following arduino header-compatible boards stm32 microcontrollers nucleo boards see next section also arduino headers nucleo boards stmicroelectronics support mbed ide development additional onboard st-link/v2-1 host adapter chip supplies swd debugging virtual com port mass storage three nucleo board families supporting different microcontroller ic package footprint debugger embedded nucleo boards converted segger j-link debugger protocol following discovery evaluation boards sold stmicroelectronics provide quick easy way engineers evaluate microcontroller chips kits available various distributors less us 20 stmicroelectronics evaluation product licence agreement forbids use production system product offered sale board includes on-board st-link programming debugging via mini-b usb connector power board provided choice 5 v via usb cable external 5 v power supply used output power supplies 3 v 5 v current must less 100 discovery boards also include voltage regulator reset button user button multiple leds swd header top board rows header pins bottom open-source project created allow linux communicate st-link debugger chibios/rt free rtos ported run discovery boards. ref name= getting started stm32vl-discovery board chibios/rt getting started stm32vl-discovery board chibios/rt /ref ref name= getting started stm32l-discovery board chibios/rt getting started stm32l-discovery board chibios/rt /ref ref name= getting started stm32f4-discovery board chibios/rt getting started stm32f4-discovery board chibios/rt /ref following evaluation kits sold stmicroelectronics ready-to-use java development kits stm32 microcontrollers stm3220g-java starter kit combines evaluation version is2t microej® software development kit sdk stm32f2 series microcontroller evaluation board providing everything engineers need start projects microej provides extended features create simulate test deploy java applications embedded systems support graphical user interface gui development includes widget library design tools including storyboarding tools customizing fonts stm32 microcontrollers embed java part number ends j like stm32f205vgt6j following evaluation kits sold partners stmicroelectronics listed st website stm32 microcontrollers rom'ed bootloader supports loading binary image flash memory using one peripherals varies stm32 family since stm32 bootloaders support loading usart peripheral boards connect usart rs-232 usb-to-uart adapter ic thus universal method program stm32 microcontroller method requires target way enable/disable booting rom'ed bootloader i.e jumper switch button amount documentation arm chips daunting especially newcomers documentation microcontrollers past decades would easily inclusive single document chips evolved documentation grown total documentation especially hard grasp arm chips since consists documents ic manufacturer stmicroelectronics documents cpu core vendor arm holdings typical top-down documentation tree manufacturer website manufacturer marketing slides manufacturer datasheet exact physical chip manufacturer detailed reference manual describes common peripherals aspects physical chip family arm core generic user guide arm core technical reference manual arm architecture reference manual describes instruction set stmicroelectronics additional documents evaluation board user manuals application notes getting started guides software library documents errata see external links section links official stm32 arm documents stm32f051r8 br stm32xxwwyz
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Computer architecture
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directx raytracing directx raytracing dxr feature microsoft directx allows hardware real-time raytracing significant advancement computer graphics first seen consumer level gpus nvidia geforce 20 series announced 2018 dxr released part new version directx rather compatible extension directx 12 windows 10 october 2018 update includes public release directx raytracing dxr introduces 4 main elements directx 12 api
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Operating systems
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moo programming language moo programming language relatively simple programming language used support moo server dynamically typed uses prototype-based object-oriented system syntax roughly derived ada school programming languages stephen white authored first moo server language 1990 using c. course year pavel curtis joined project releasing first version lambdamoo server lambdamoo run maintained entirely volunteer basis sourceforge project although last packaged release 2000 development still active project cvs white describes moo mishmash c-like operators ada-like control structures combined prototype-style single-inheritance language explicit exception handling control flow well traditional looping constructs verb property hierarchy provides default values prototype objects over-riding values lower hierarchy hierarchy objects maintained delegation object parent property resulting form single inheritance special security-related attributes objects verbs properties include ownership read write execute flags moo programs byte-code compiled implicit decompilation editing providing canonical form programs moo programs orthogonally persistent periodic checkpoints objects identified unique integer identifier unused program data eliminated automatic garbage collection implemented reference counting however moo objects garbage collected manually deleted owners superusers aka wizards process called 'recycling moo explicitly multi-user system programs verbs contributed number connected users distinction made 'driver runtime 'core programs written moo language vast majority functionality running moo handled 'in-core runtime supports multi-tasking using retribution based time slicing method verbs run exclusive access database explicit locking necessary maintain synchronization simple tcp/ip messaging telnet compatible used communicate client sockets identified 'player virtual reality representation system language supports weak references objects number properties verbs strings built-in functions retrieve lists properties verbs exist giving language runtime facilities reflection server also contains support wildcard verb matching code easily used handle multiple commands similar names functions available sequence types moo lists strings support random access well head tail operations similar available lisp operations lists strings non-destructive non-object datatypes immutable built-in functions libraries allow lists also used associative arrays ordered unordered sets moo basic set control structures for-in-list fancy feature classic hello world program written moo interesting example
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Programming language topics
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wuala wuala secure online file storage file synchronization versioning backup service originally developed run caleido inc part lacie turn owned seagate technology service stores files data centres provided wuala multiple european countries france germany switzerland earlier version also supported distributed storage users machines however feature dropped 17 august 2015 wuala announced discontinuing service stored data would deleted 15 november 2015 wuala recommended rival cloud storage startup tresorit alternative remaining customers research development occurred swiss federal institute technology eth zürich 14 august 2008 19 september 2008 26 october 2008 16 december 2008 19 march 2009 5 january 2010 23 may 2011 28 september 2011 11 june 2014 31 october 2014 17 august 2015 registered user registered unregistered users receive streaming media user adds file wuala saves changes file served wuala user local copy file first encrypted chunked redundant fragments using reed-solomon error correction codes fragments uploaded data centers wuala offered free accounts 5 gb storage charge 11 june 2014 shifted paid-only service end 2014 longer support form free-only storage shifting entirely payment based usage model users joint products may start greater amounts storage limited period lacie external hard disk drive 10 gb one year lacie usb flash drive 4 gb two years additional storage may bought june 2014 referral system shut due new paid-only policy bought storage prices range 29 eur/year 20 gb 999 eur/year 1 tb pricing changed june 2014 storage plan starts 0.99 € per month 9 € per year 5 gb ends 159.90 € per month 1799 € per year 2 tb storage one distinguishing features wuala ability trade local disk storage space cloud storage longer available user interface offers features normally associated file manager additional features come integration registered user install java-based client application swt-gui web browser computer java installed computer without java running class loader prevented support following may limited according wuala faq software uses aes-256 encryption rsa-2048 key exchange signatures keys organized key management scheme called cryptree according faq wuala employs full client-side encryption files metadata – os x metadata supported – get encrypted uploaded encryption key stored one even lacie operates service decrypt stored files disadvantage wuala password recovery data processing needs done client example creating search index advantage significantly improved privacy since source code wuala released difficult ensure software states including proper client-side encryption also updates pushed automatically client machine facts mean users wuala safe possible backdoors code
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Computer file systems
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scieno sitter scieno sitter content-control software installed computer blocks certain websites critical scientology viewed software released church scientology 1998 church members using windows 95 term scieno sitter coined critics scientology assert program form internet censorship program started late summer 1998 scientologists mailed software cds told program would help members build web sites would link scientology main site however recipients program told also censorship program blocked critical sites viewed user computer sites deemed dangerous critics scientology referred program cult mind-control 21st century asserted stifles freedom speech one software developer stated though thought spam filters general good idea found disturbing huge number terms banned completely unrelated stated goals however vice president office special affairs branch scientology stated scientologists make personal choice whether use filtering software different spokesperson claimed members scientology asked software stating many parishioners want use internet asked filter protection elements sought twist pervert religion packaging cd mailed users specifically request filter states popular demand scientologists program developed prevent subjected 'entheta hate mail internet filter allows direct access sites rapidly without dev-t 'd vilifying material forgeries hate messages fashion attention remain focused dissemination setting people feet bridge total freedom order gain access software scientologists must first sign contract section 7 contract states members must agree use specific internet filter program csi provided allows freedom view sites dianetics scientology principals without threat accessing sites deemed using marks works unauthorized fashion deemed improper discreditable scientology religion program works preventing user accessing sites certain keywords scientology identified objectionable material viewing members use keywords functions way prevent members learning guarded scientology doctrine xenu ot iii material relating space opera scientology scripture keywords notable topics blocked program include names several notable critics scientology including robert vaughn young keith henson well several hundred frequent participants alt.religion.scientology newsgroup together terms like suppressive person lisa mcpherson screening process limited viewing web sites however also blocks users discussing forbidden keywords chat programs internet relay chat keywords mentioned certain individuals identified undesirable enter chat room user kicked discussion tory christman worked operative osa osa operatives removed program computer allow analyze critical material spread internet scientology time software removed christman encountered operation clambake web site online discussions operator andreas heldal-lund eventually led leaving scientology public announcement alt.religion.scientology december 1998 software discussed e network program investigative reports program showed web page operation clambake described software piece entitled church scientology—afraid real world censors net members bob minton quoted report stating scientologists given filtering software allow go internet want scientologists subjected critical information 2006 film bridge scientologist character diane wheat attempts find information internet google search word zeenu directed search word xenu operation clambake web site comes first search results wheat attempts view site message appears computer stating page requested identified containing racist/hate-oriented material scientology symbol displayed left-hand side warning box
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Web technology
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mac-forced forwarding mac-forced forwarding macff used control unwanted broadcast traffic host-to-host communication achieved directing network traffic hosts located subnet different locations upstream gateway device provides security layer 2 since traffic able pass directly hosts macff suitable ethernet networks layer 2 bridging device known ethernet access node ean connects access routers clients macff configured eans macff described rfc 4562 mac-forced forwarding method subscriber separation ethernet access network allied telesis switches implement macff using dhcp snooping maintain database hosts appear switch port host tries access network switch port dhcp snooping checks host ’ ip address database ensure host valid macff uses dhcp snooping check whether host gateway access router macff uses form proxy arp reply arp requests giving router mac address forces host send traffic router even traffic destined host subnet source router receives traffic makes forwarding decisions based set forwarding rules typically qos policy set filters
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Internet protocols
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configuration menu language configuration menu language cml used linux kernel versions prior 2.5.45 configure values determine composition exact functionality kernel many possible variations kernel functionality exist customization possible instance specifications exact hardware run also tuned administrator preferences cml written raymond chen 1993 question-and-answer interface allowed systematic selection particular behaviors without editing multiple system files eric s. raymond wrote menu-driven module named cml2 replace officially rejected linus torvalds attributed rejection 2007 lkml.org post preference small incremental changes concern maintainer involved rewrite ca n't ... go thing expect merged said noting raymond left splash rejection linuxkernelconf replaced cml kernel version 2.5.45 remains use 4.0 kernel
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Computer architecture
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workload manager ibm mainframes workload manager wlm base component mvs/esa mainframe operating system successors including z/os controls access system resources work executing z/os based administrator-defined goals workload manager components also exist operating systems example ibm workload manager also software product aix operating system mainframe computer many different applications execute time expectations executing work consistent execution times predictable access databases z/os workload manager wlm component fulfills needs controlling work access system resources based external specifications system administrator system administrator classifies work service classes classification mechanism uses work attributes like transaction names user identifications program names specific applications known use addition system administrator defines goals importance levels service classes representing application work goals define performance expectations work goals expressed response times relative speed termed velocity discretionary specific requirement exists response time describes duration work requests entered system application signals wlm execution completed wlm interested assure average response time set work requests ends expected time percentage work requests fulfill expectations end user definition response time also requires applications communicate wlm possible relative speed measure – named execution velocity used describe end user expectation system measurement based system states continuously collected system states describe work request uses system resource must wait used work latter named delay state quotient using states productive states using delay states multiplied 100 execution velocity measurement require communication application wlm component also abstract response time goal finally system administrator assigns importance service class tell wlm service classes get preferred access system resources system load high allow work execute service classes goal definitions organized service policies together constructs reporting controlling saved service definition access wlm active service definition saved couple data set allows z/os systems parallel sysplex cluster access execute towards performance goals wlm closed control mechanism continuously collects data work system resources compares collected aggregated measurements user definitions service definition adjusts access work system resources user expectations achieved mechanism runs continuously pre-defined time intervals order compare collected data goal definitions performance index calculated performance index service class single number tells whether goal definition could met overachieved missed wlm modifies access service classes based achieved performance index importance uses collected data project possibility result change change executed forecast comes result beneficial work based defined customer expectations wlm uses data base ranging 20 seconds 20 minutes contain statistically relevant basis samples calculations also one decision interval change performed benefit one service class maintain controlled predictable system wlm controls access work system processors i/o units system storage starts stops processes work execution access system processors example controlled dispatch priority defines relative ranking units work want execute dispatch priority assigned units work classified service class already stated dispatch priority fixed simply derived importance service class changes based goal achievement system utilization demand work system processors similar mechanisms exist controlling system resources way z/os workload manager controlling access work system resources named goal oriented workload management contrast resource entitlement based workload management defines much static relationship work access system resources resource entitlement based workload management found larger unix operating systems example major difference workload management components operating systems close cooperation z/os workload manager major applications middleware subsystems executing z/os wlm offers interfaces allow subsystems tell wlm unit work starts ends system pass classification attributes used system administrator classify work system addition wlm offers interfaces allow load balancing components place work requests best suited system parallel sysplex cluster additional instrumentation exists helps database resource managers signal contention situations wlm wlm help delayed work promoting holder resource locks latches time z/os workload manager became central control component performance related aspects z/os operating system parallel sysplex cluster z/os workload manager components work together provide single image view executing applications cluster system z multiple virtual partitions z/os wlm allows interoperate lpar hypervisor influence weighting z/os partitions control amount cpu capacity consumed logical partitions
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Operating systems
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hp 95lx hp 95lx palmtop pc f1000a f1010a also known project jaguar hewlett packard first ms-dos-based pocket computer personal digital assistant introduced april 1991 collaboration lotus development corporation seen successor series larger portable pcs like hp 110 hp 110 plus hp 95lx nec v20 cpu intel 8088 clone running 5.37 mhz intel corporation system chip soc device considered completely pc-compatible quarter-cga mda resolution lcd screen ran microsoft ms-dos version 3.22 customized version lotus 1-2-3 release 2.2 built software read-only memory rom included calculator appointment calendar telecommunications program simple text editor also included cr 2032 lithium coin cell memory backup two aa main batteries run mass storage hp 95lx single pcmcia slot could hold static ram card cr 2025 back-up coin cell rs-232-compatible serial port provided well infrared port printing compatible models hewlett packard printers character mode display showed 16 lines 40 characters backlight ibm compatible pcs work hardware code page 437 hp 95lx text mode font hard-wired code page 850 instead lotus 1-2-3 internally used lotus international character set lics characters translated code page 850 display printing purposes successor models hp 95lx include hp 100lx hp palmtop fx hp 200lx hp 1000cx hp omnigo 700lx
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Computer architecture
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volume computing computer data storage volume logical drive single accessible storage area single file system typically though necessarily resident single partition hard disk although volume might different physical disk drive still accessed operating system logical interface however volume differs partition volume thing partition example floppy disk might accessible volume even though contain partition floppy disks partitioned modern computer software also os recognize partition without recognizing volume associated os interpret filesystem stored situation occurs example windows nt-based oses encounter disks non-microsoft os partitions ext3 filesystem commonly used linux another example occurs intel world extended partition partitions contain filesystem directly instead logical drives aka volumes must created within also case netware volumes residing inside single partition short volumes exist logical os level partitions exist physical media specific level sometimes one-to-one correspondence guaranteed microsoft windows server 2008 onward term volume used superset includes partition well n't uncommon see volume packed single file examples include iso9660 disc images cd/dvd images commonly called isos installer volumes mac os x dmgs volumes files reside within another volume certainly partitions example concerns windows xp system two physical hard disks first hard disk two partitions second one first partition first hard disk contains operating system mount points left defaults example linux systems volumes usually handled logical volume manager enterprise volume management system manipulated using mount 8 nt-based versions microsoft windows volumes handled kernel managed using disk management mmc snap-in diskpart command line tool important note windows nt-based oses single root directory result windows assign least one path mounted volume take one two forms two examples file called track 1.mp3 stored root directory mounted volume could referred codice_2 codice_3 respectively order assign mount point volume path within another volume following criteria must met default windows assign drive letters drives follows legacy convention operating system startup drive still commonly assigned c however always case since personal computers longer include floppies optical disc removable drives typically still start letters b available manual assignment user administrative privileges assignment remembered os pc next time removable volume inserted long conflicts long removable drive reformatted another computer changes volume serial number long os reinstalled computer windows xp mount points may managed disk management snap-in microsoft management console conveniently accessed computer management administrative tools section control panel one drive letter refer single volume using subst command warning removing drive letters mount-points drive may break programs files may accessible known path example program installed \program files\some program may expect find data files \program files\some program\data logical disk previously called drive letter changed e program wo n't able find data \program files\some program\data since drive letter longer represents volume unix-like operating systems volumes boot volume mount-point somewhere within filesystem represented path logically directory tree stored volume grafted mountpoint convention mount-points often placed directory called '/mnt though '/media terms sometimes used use given path mount-point another volume empty directory sometimes called folder must exist unix-like operating systems use mount command manipulate mount points volumes example cd-rom drive containing text file called 'info.txt mounted '/mnt/iso9660 text file would accessible '/mnt/iso9660/info.txt files within volume generally moved place within volume manipulating filesystem without moving actual data however file moved outside volume data must relocated much expensive operation order better visualize concept one might consider example large library non-fiction work originally classified subject plants moved subject flora one need refile book whose position shelf would static rather one needs replace index card however move book another library adjusting index cards alone insufficient entire book must moved volume label name given specific volume filesystem fat filesystem volume label traditionally restricted 11 characters reflecting 8.3 restrictions divided name extension fields even long file name enabled stored entry within disk root directory special volume-label attribute bit set also copied 11-byte field within extended bios parameter block disk boot sector label always stored uppercase fat vfat filesystems contain special characters also disallowed regular filenames ntfs filesystem length volume label restricted 32 characters include lowercase characters even unicode label command used change label dos windows os/2 gui systems like windows explorer pressed volume highlighted right-click name bring context menu allows renamed either process renaming file changing label windows also change volume creation timestamp current date time fat filesystems ntfs partitions system volume information directory whose creation timestamp set windows creates partition first recognizes repartitioning creation new volume separate disk utility contrast label volume serial number generally unique normally changed user thus acts consistent reliable identifier volume changed disk removed another inserted disk formatting changes serial number relabeling vol command used command line display current label serial number volume
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Computer file systems
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three-address code computer science three-address code often abbreviated tac 3ac intermediate code used optimizing compilers aid implementation code-improving transformations tac instruction three operands typically combination assignment binary operator example codice_1 name derives use three operands statements even though instructions fewer operands may occur since three-address code used intermediate language within compilers operands likely concrete memory addresses processor registers rather symbolic addresses translated actual addresses register allocation also uncommon operand names numbered sequentially since three-address code typically generated compiler refinement three-address code a-normal form anf three-address code would broken several separate instructions instructions translate easily assembly language also easier detect common sub-expressions shortening code following example one calculation composed several smaller ones three-address code may conditional unconditional jumps methods accessing memory may also methods calling functions may reduce jumps way three-address code may useful control-flow analysis following c-like example loop stores squares numbers 0 9
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Programming language topics
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s60 software platform s60 platform formerly series 60 user interface software platform smartphones runs top symbian operating system created nokia based 'pearl user interface symbian ltd introduced comdex november 2001 first shipped nokia 7650 smartphone platform since seen 5 updated editions series 60 renamed s60 november 2005 2008 symbian foundation formed consolidate assets different symbian platforms s60 uiq moap making open source 2009 based code base s60 first iteration platform since creation symbian foundation launched s60 5th edition symbian^1 top symbian os 9.4 base subsequent iterations named symbian^2 japanese market symbian^3 s60 software multivendor standard smartphones supports application development java midp c++ python adobe flash api called avkon ui s60 consists suite libraries standard applications telephony personal information manager pim tools helix-based multimedia players intended power fully featured modern phones large colour screens commonly known smartphones originally distinguishing feature s60 phones allowed users install new applications purchase unlike standard desktop platform however built-in apps rarely upgraded vendor beyond bug fixes new features added phones developed rather public release certain buttons standardized menu key four way joystick d-pad left right soft keys clear key s60 mainly used nokia also licensed manufacturers including lenovo lg electronics panasonic samsung sendo siemens mobile sony ericsson solstice vertu sony ericsson notably main vendor using competing uiq symbian interface addition manufacturers community includes four major releases s60 series 60 2001 series 60 second edition 2002 s60 3rd edition 2005 s60 5th edition 2008 release updated version called feature pack sometimes known relay runs different symbian version many devices capable running s60 software platform symbian os devices ranging early nokia 7650 running s60 v0.9 symbian os v6.1 latest samsung i8910 omnia hd running s60 v5.0 symbian os v9.4 symbian^3 version revised platform v5.2 table lists devices carrying version s60 well symbian os version based note new devices since symbian^3 may capable upgrading later systems symbian anna symbian belle therefore may see device listed many systems symbian progressing period organisational change metamorph open source software platform project os symbian os originally provided user interface ui visual layer runs atop operating system implemented separately examples symbian uis moap series 60 series 80 series 90 uiq separation ui underlying os created flexibility confusion market place nokia purchase symbian brokered involvement ui developers major user interface layers pledged donated open source foundation independently symbian operating system new symbian foundation announced intent unify different symbian uis single ui based s60 platform announcements made march 2009 indicated would s60 5th edition feature pack 1 12 april 2011 nokia announced symbian anna software update symbian^3 release three new devices 500 x7 e6 announced symbian anna pre-installed symbian anna available software update symbian^3 based devices well significant updates come anna 24 august 2011 nokia announced symbian belle later renamed nokia belle software update symbian anna release three new devices 603 700 701 nokia 600 cancelled replaced nokia 603 announced symbian belle pre-installed symbian belle available software update symbian anna-based devices well significant updates came belle november 2011 nokia announced carla donna updates carla expected released late 2012 early 2013 feature new web browser new widgets new nfc capabilities dolby surround audio enhancement donna going dual-core processor exclusive planned released late 2013 early 2014 may 2012 nokia executive claimed carla donna cancelled nokia would instead release belle feature pack 2 later 2012 lacking many new features planned carla donna february 2011 nokia announced partnership microsoft adopt windows phone 7 nokia primary operating system leaving symbian development question nokia promised support symbian newer devices least 2016 new symbian devices released nokia 808 pureview 29 april 2011 nokia announce would transfer symbian activities accenture along 3,000 employees symbian belle symbian belle – facts features pictures
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Operating systems
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socket am4 socket am4 microprocessor socket used amd central processing units cpus built zen including zen+ zen 2 excavator microarchitectures am4 launched september 2016 designed replace sockets am3+ fm2+ fs1b single platform 1331 pin slots first amd support ddr4-compatible memory well achieve unified compatibility high-end cpus previously using socket am3+ amd lower-end apus various sockets am4 socket specifies 4 holes fastening heatsink motherboard placed corners rectangle lateral length 54×90 mm previous sockets 48×96 mm heat sinks older sockets compatible however cooler manufacturers reported offering brackets allowing previously manufactured coolers work am4 coolers redesigned alternatively motherboard makers including am3 am4 cooler mounting holes allowing previous generation coolers used socket am4 currently base 6 chipset models processors socket designed systems chip soc traditional northbridge southbridge board processor motherboard chipset increase number pci express lanes connectivity options connectivity options include nvme sata usb 3.2 gen 2
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Computer architecture
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amazon web services amazon web services aws subsidiary amazon provides on-demand cloud computing platforms individuals companies governments metered pay-as-you-go basis aggregate cloud computing web services provide set primitive abstract technical infrastructure distributed computing building blocks tools one services amazon elastic compute cloud allows users disposal virtual cluster computers available time internet aws version virtual computers emulate attributes real computer including hardware central processing units cpus graphics processing units gpus processing local/ram memory hard-disk/ssd storage choice operating systems networking pre-loaded application software web servers databases customer relationship management crm etc aws technology implemented server farms throughout world maintained amazon subsidiary fees based combination usage hardware/os/software/networking features chosen subscriber required availability redundancy security service options subscribers pay single virtual aws computer dedicated physical computer clusters either part subscription agreement amazon provides security subscribers system aws operates many global geographical regions including 6 north america 2017 aws comprised 90 165 2019 services spanning wide range including computing storage networking database analytics application services deployment management mobile developer tools tools internet things popular include amazon elastic compute cloud ec2 amazon simple storage service amazon s3 services exposed directly end users instead offer functionality apis developers use applications amazon web services offerings accessed http using rest architectural style soap protocol amazon markets aws subscribers way obtaining large scale computing capacity quickly cheaply building actual physical server farm services billed based usage service measures usage varying ways 2017 aws owns dominant 34 cloud iaas paas next three competitors microsoft google ibm 11 8 6 respectively according synergy group aws platform launched july 2002 early stages platform consisted disparate tools services late 2003 aws concept publicly reformulated chris pinkham benjamin black presented paper describing vision amazon retail computing infrastructure completely standardized completely automated would rely extensively web services services storage would draw internal work already underway near end paper mentioned possibility selling access virtual servers service proposing company could generate revenue new infrastructure investment november 2004 first aws service launched public usage simple queue service sqs thereafter pinkham lead developer christopher brown developed amazon ec2 service team cape town south africa amazon web services officially re-launched march 14 2006 combining three initial service offerings amazon s3 cloud storage sqs ec2 aws platform finally provided integrated suite core online services chris pinkham benjamin black proposed back 2003 service offered developers web sites client-side applications companies andy jassy aws founder vice president 2006 said time amazon s3 one first scalable elements aws helps free developers worrying going store data whether safe secure available need costs associated server maintenance whether enough storage available amazon s3 enables developers focus innovating data rather figuring store it. 2016 jassy promoted ceo division reflecting success aws annual compensation 2017 hit nearly 36 million support industry-wide training skills standardization aws began offering certification program computer engineers april 30 2013 highlight expertise cloud computing james hamilton aws engineer wrote retrospective article 2016 highlight ten-year history online service 2006 2016 early fan outspoken proponent technology joined aws engineering team 2008 january 2018 amazon launched autoscaling service aws november 2018 aws announced customized arm cores use servers also november 2018 aws developing ground stations communicate customer satellites november 2010 reported amazon.com retail sites migrated aws prior 2012 aws considered part amazon.com revenue delineated amazon financial statements year industry watchers first time estimated aws revenue 1.5 billion april 2015 amazon.com reported aws profitable sales 1.57 billion first quarter year 265 million operating income founder jeff bezos described fast-growing 5 billion business analysts described surprisingly profitable forecast october 2015 amazon.com said q3 earnings report aws operating income 521 million operating margins 25 percent aws 2015 q3 revenue 2.1 billion 78 increase 2014 q3 revenue 1.17 billion 2015 q4 revenue aws segment increased 69.5 y/y 2.4 billion 28.5 operating margin giving aws 9.6 billion run rate 2015 gartner estimated aws customers deploying 10x infrastructure aws combined adoption next 14 providers 2016 q1 revenue 2.57 billion net income 604 million 64 increase 2015 q1 resulted aws profitable amazon north american retail business first time first quarter 2016 amazon experienced 42 rise stock value result increased earnings aws contributed 56 corporate profits aws 17.46 billion annual revenue 2017 end 2018 number grown 25.65 billion notable customers include nasa obama presidential campaign 2012 netflix 2019 reported 80 germany listed dax companies use aws 2019 aws distinct operations 20 geographical regions 6 north america 1 south america 5 emea 8 asia pacific aws announced 5 new regions coming online hong kong sar bahrain milan cape town jakarta region wholly contained within single country data services stay within designated region region multiple availability zones consist one discrete data centers redundant power networking connectivity housed separate facilities availability zones automatically provide additional scalability redundancy within region since intentionally isolated prevent outages spreading zones several services operate across availability zones e.g. s3 dynamodb others configured replicate across zones spread demand avoid downtime failures december 2014 amazon web services operated estimated 1.4 million servers across 28 availability zones global network aws edge locations consists 54 points presence worldwide including locations united states europe asia australia south america 2014 aws claimed aim achieve 100 renewable energy usage future united states aws partnerships renewable energy providers include community energy virginia support us east region pattern development january 2015 construct operate amazon wind farm fowler ridge iberdrola renewables llc july 2015 construct operate amazon wind farm us east edp renewables north america november 2015 construct operate amazon wind farm us central tesla motors apply battery storage technology address power needs us west northern california region aws also pop-up lofts different locations around world market aws entrepreneurs startups different tech industries physical location visitors work relax inside loft learn aws june 2014 aws opened first temporary pop-up loft san francisco may 2015 expanded new york city september 2015 expanded berlin aws opened fourth location tel aviv march 1 2016 march 22 2016 pop-up loft open london september 10 october 29 2015 2017 aws launched amazon start united kingdom help young adults military veterans retrain technology-related skills partnership prince trust ministry defence mod aws help provide re-training opportunities young people disadvantaged backgrounds former military personnel aws working alongside number partner companies including cloudreach sage edf energy tesco bank
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Distributed computing architecture
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midnightbsd midnightbsd free unix-like desktop-oriented operating system originally forked freebsd 6.1 periodically updated code drivers later freebsd releases default desktop environment gnustep borrows heavily nextstep graphical user interface midnightbsd began fork freebsd 2005 founder project lucas holt wished create bsd derived desktop operating system familiar several live cd projects work trueos desktopbsd time also interest gnustep two ideas folded plan create user friendly desktop environment midnightbsd 0.1 released based efforts lucas holt caryn holt d. adam karim phil pereira bsdnexus christian reinhardt release features modified version freebsd ports system ports system evolved mports includes fake support generation packages installation license tagging strict rules package list generation modification files outside destination many features introduced midnightbsd 0.1.1 christian reinhardt replaced phil pereira lead mports maintainer prior release midnightbsd 0.1 d. adam karim acted security officer first release release engineering handled lucas holt 0.2 introduced refined mports system 2000 packages portable c compiler added i386 addition gnu compiler collection changes include enabling ipfw sound card detection startup newer versions many software packages including bind gcc openssh sendmail well live cd creation system currently project focusing finishing magus build cluster software creating new installer finishing new package installation management tools called mport beginning work 0.3 release next release feature enhancements found freebsd 7.0 dragonfly bsd midnightbsd named lucas caryn holt cat midnight midnight ten-pound black turkish angora midnightbsd released several licenses kernel code newly created code released two-clause bsd license parts gpl lgpl isc beerware licenses along three- four-clause bsd licenses jesse smith reviewed midnightbsd 0.6 distrowatch weekly
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Operating systems
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automatic complaint-letter generator automatic complaint-letter generator website automatically generates complaint letters website created scott pakin 1994 allows users submit name individual company complaint directed toward program generates complaint letter general enough true fit anyone everyone yet specific enough mean something scott pakin started website april 1994 undergraduate student studying computer science carnegie mellon university began thinking creating program would generate complaint letters idea originated looked pointless ramblings student newspaper pakin criticized letters quality one friends remarked letters sounded arbitrary computer could written pakin pondered comment decided write program would generate complaints website allows users specify name individual company complaint directed toward well number paragraphs complaint submitting data computer generates sentences composed arbitrary verbs nouns adjectives 1995 generator 282 sentence skeletons 170 independent clauses 183 adjectives 123 nouns combination elements form one billion sentences september 2009 generator expanded 3379 independent clauses 618 adjectives 497 nouns complaint letters randomly generated insult different pakin said people read letters inclined pay attention sentences accurate ignored statements obviously wrong noted complaint generator general enough true fit anyone everyone yet specific enough mean something 2001 paul weyland chosen austin toastmasters club present kirk watson mayor austin texas toastmasters member asked weyland speech went automatic complaint-letter generator typed mayor name generator churned four-page complaint letter weyland accidentally emailed mayor even though meant send fellow toastmaster member joke watson learned joke indicated would attending club meeting security issues aide e-mailed weyland said mayor joking meeting weyland apologized mayor fawning introductory speech mayor responded ou know paul rant accused lips planted posteriors drug-addled sycophants 'll notice paul lips attached posterior evening
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Computational linguistics
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trojan.win32.dnschanger trojan.win32.dnschanger trojan win32/dnschanger microsoft malware protection center definition multiple av-labs backdoor trojan due mcafee labs malware variant detected april 19 2009 though microsoft malware protection center knew threat since december 8 2006 dns changer trojans dropped onto systems malware tdss koobface dns-changer-trojan malicious .exe file unable spread accord may therefore perform several actions attacker choice compromised computer changing domain name server dns settings order divert traffic unsolicited potentially illegal and/or malicious domains win32.dnschanger used organized crime syndicates maintain click-fraud moment unaware user browsing activity secretly manipulated altering user clicks seemingly legitimate link forwarded another offered site attackers generate revenues pay-per-click online advertising schemes mostly trojan usually extremely small file +/- 1.5 kilobytes designed change 'nameserver registry key value custom ip address link called ip address encrypted body trojan result change victim device contact newly assigned dns -server resolve names different webservers sometimes randomly f-secure received samples variant named paypal-2.5.200-mswin32-x86-2005.exe case paypal attribution indicates phishing likely trojan programmed change dns server name victim computer ip address 193.227.227.218 registry key affected trojan
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Computer security
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openbsd cryptographic framework openbsd cryptographic framework ocf service virtualization layer uniform management cryptographic hardware operating system part openbsd project included operating system since openbsd 2.8 december 2000 like openbsd projects openssh ported systems based berkeley unix freebsd netbsd solaris linux one linux ports supported intel use proprietary cryptographic software hardware provide hardware-accelerated ssl encryption open source apache http server cryptography computationally intensive used many different contexts software implementations often serve bottleneck information flow increase network latency specialist hardware cryptographic accelerators mitigate bottleneck problem introducing parallelism certain kinds hardware hardware random number generators also produce randomness reliably pseudo-random software algorithm exploiting entropy natural events unlike graphics applications games film processing similar hardware accelerators common use strong operating system support use hardware cryptography relatively low uptake late 1990s need uniform operating system layer mediate cryptographic hardware application software used lack layer led production applications hard-coded work one small range cryptographic accelerators openbsd project history integrating strong carefully audited cryptography operating system core produced framework provision cryptographic hardware acceleration operating system service application-level support provided pseudo-device provides access hardware drivers standard ioctl interface simplifies writing applications removes need application programmer understand operational details actual hardware used openbsd implementation ipsec packet-level encryption protocol altered packets decoded batches improves throughput one rationale maximize efficiency hardware usage—larger batches reduce bus transmission overhead—but practice ipsec developers found strategy improves efficiency even software implementations many intel firmware hubs i386 motherboards provide hardware random number generator possible facility used provide entropy ipsec openssl uses ocf systems hardware supports rsa dh dsa cryptographic protocols automatically use hardware without modification software 11 december 2010 former government contractor named gregory perry sent email openbsd project leader theo de raadt alleging fbi paid openbsd ex-developers 10 years previously compromise security system inserting number backdoors side channel key leaking mechanisms ocf theo de raadt made email public 14 december forwarding openbsd-tech mailing list suggested audit ipsec codebase de raadt response skeptical report invited developers independently review relevant code weeks followed bugs fixed evidence backdoors found oracle proprietary operating system solaris originally developed sun features unrelated product called solaris cryptographic framework plug-in system cryptographic algorithms hardware
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Operating systems
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