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data theft data theft growing phenomenon primarily caused system administrators office workers access technology database servers desktop computers growing list hand-held devices capable storing digital information usb flash drives ipods even digital cameras since employees often spend considerable amount time developing contacts confidential copyrighted information company work may feel right information inclined copy and/or delete part leave company misuse still employment sold bought used criminals criminal organizations alternatively employee may choose deliberately abuse trusted access information purpose exposing misconduct employer perspective society act whistleblowing seen positive certain situations protected law jurisdictions usa common scenario sales person makes copy contact database use next job typically clear violation terms employment notable acts data theft include leaker chelsea manning self-proclaimed whistleblowers edward snowden hervé falciani phrase data theft actually misnomer since unlike theft typical data theft methods typically deprive owner data rather create additional unauthorized copy thumbsucking similar podslurping intentional undeliberate use portable usb mass storage device usb flash drive thumbdrive illicitly download confidential data network endpoint usb flash drive allegedly used remove without authorization highly classified documents design u.s. nuclear weapons vault los alamos threat thumbsucking amplified number reasons including following techniques investigate data theft include stochastic forensics digital artifact analysis especially usb drive artifacts computer forensics techniques countries term incorrect considered theft thing material object information thing
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Computer security
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virtual switch redundancy protocol virtual switch redundancy protocol vsrp proprietary network resilience protocol developed foundry networks currently sold products manufactured brocade communications systems formerly foundry networks hewlett packard protocol differs many others use combines layer 2 layer 3 resilience – effectively jobs spanning tree protocol virtual router redundancy protocol time whilst restrictions physical topologies able make use vsrp mean less flexible stp vrrp significantly improve failover times provided either protocols
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Internet protocols
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packagekit packagekit free open-source suite software applications designed provide consistent high-level front end number different package management systems packagekit created richard hughes 2007 first introduced operating system default application may 2008 release fedora 9 suite cross-platform though primarily targeted linux distributions follow interoperability standards set freedesktop.org group uses software libraries provided d-bus polkit projects handle inter-process communication privilege negotiation respectively since 1995 package formats around since 2000 dependency solvers auto-downloaders layer top around since 2004 graphical front-ends packagekit seeks introduce automatic updates without authenticate root fast-user-switching warnings translated correct locale common upstream gnome kde tools one software multiple linux distributions packagekit active maintenance since 2014 packagekit runs system-activated daemon codice_1 abstracts differences different systems library called codice_2 allows programs interact packagekit features include graphical front-ends packagekit include pkcon operates command-line number different package management systems known back-ends support different abstract methods signals used front-end tools back-ends supported include
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Operating systems
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bank panic bank panic arcade game developed sanritsu manufactured sega 1984 bally/midway manufactured game america player assumes part old west sheriff must protect bank customers masked robbers layout bank implicitly circle twelve numbered doors player center player rotate left right view three doors time doors open reveal customer drop bag money making deposit robber attempt shoot player young boy holding stack three five hats player rapidly shoot bag money bonus time level ends twelve doors received one deposits indicated numbered boxes across top screen red dollar sign showing door completed deposit random intervals bomb placed one doors rapid timer count 99 player must move door destroy bomb gunfire shooting customer shot robber failing destroy bomb failing complete level overall timer runs shown bar bottom screen costs player one life robbers wear white boots robbers need shot twice eliminated level starts word fair displayed cuckoo clock shooting robber sight deemed unfair robber incurs penalty however timer appear player fast enough shooting robber timer counts eventually averages timer cuckoo clock determines bonus points shooting robber timer showing 0:00 earns larger amount bonus points shooting robber red shirt earns maximum bonus points available 5,000 shooting robber red shirt timer says 0:00 lights letter word extra shown bottom screen lighting whole word earns extra life even bonus points automatic advancement next level due bug high score table shown game ends never attract mode west bank clone dinamic software zx spectrum commodore 64 msx amstrad cpc atari 8-bit family clone released 1992 bang bank hotel panic clone android
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Computer architecture
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differential cryptanalysis differential cryptanalysis general form cryptanalysis applicable primarily block ciphers also stream ciphers cryptographic hash functions broadest sense study differences information input affect resultant difference output case block cipher refers set techniques tracing differences network transformation discovering cipher exhibits non-random behavior exploiting properties recover secret key cryptography key discovery differential cryptanalysis generally attributed eli biham adi shamir late 1980s published number attacks various block ciphers hash functions including theoretical weakness data encryption standard des noted biham shamir des surprisingly resistant differential cryptanalysis small modifications algorithm would make much susceptible 1994 member original ibm des team coppersmith published paper stating differential cryptanalysis known ibm early 1974 defending differential cryptanalysis design goal according author steven levy ibm discovered differential cryptanalysis nsa apparently well aware technique ibm kept secrets coppersmith explains discussions nsa decided disclosure design considerations would reveal technique differential cryptanalysis powerful technique could used many ciphers turn would weaken competitive advantage united states enjoyed countries field cryptography within ibm differential cryptanalysis known t-attack tickle attack des designed resistance differential cryptanalysis mind contemporary ciphers proved vulnerable early target attack feal block cipher original proposed version four rounds feal-4 broken using eight chosen plaintexts even 31-round version feal susceptible attack contrast scheme successfully cryptanalyze des effort order 2 chosen plaintexts differential cryptanalysis usually chosen plaintext attack meaning attacker must able obtain ciphertexts set plaintexts choosing however extensions would allow known plaintext even ciphertext-only attack basic method uses pairs plaintext related constant difference difference defined several ways exclusive xor operation usual attacker computes differences corresponding ciphertexts hoping detect statistical patterns distribution resulting pair differences called differential statistical properties depend upon nature s-boxes used encryption attacker analyses differentials δ δ δ x ⊕ δ ⊕ x ⊕ denotes exclusive s-box basic attack one particular ciphertext difference expected especially frequent way cipher distinguished random sophisticated variations allow key recovered faster exhaustive search basic form key recovery differential cryptanalysis attacker requests ciphertexts large number plaintext pairs assumes differential holds least r − 1 rounds r total number rounds attacker deduces round keys final round possible assuming difference blocks final round fixed round keys short achieved simply exhaustively decrypting ciphertext pairs one round possible round key one round key deemed potential round key considerably often key assumed correct round key particular cipher input difference must carefully selected attack successful analysis algorithm internals undertaken standard method trace path highly probable differences various stages encryption termed differential characteristic since differential cryptanalysis became public knowledge become basic concern cipher designers new designs expected accompanied evidence algorithm resistant attack many including advanced encryption standard proven secure attack attack relies primarily fact given input/output difference pattern occurs certain values inputs usually attack applied essence non-linear components solid component usually fact look-up tables s-boxes observing desired output difference two chosen known plaintext inputs suggests possible key values example differential 1 1 implying difference least significant bit lsb input leads output difference lsb occurs probability 4/256 possible non-linear function aes cipher instance 4 values 2 pairs inputs differential possible suppose non-linear function key xor'ed evaluation values allow differential 2,3 4,5 attacker sends values 6 7 observes correct output difference means key either 6 ⊕ k 2 6 ⊕ k 4 meaning key k either 2 4 essence n-bit non-linear function one would ideally seek close 2 possible achieve differential uniformity happens differential attack requires much work determine key simply brute forcing key aes non-linear function maximum differential probability 4/256 entries however either 0 2 meaning theory one could determine key half much work brute force however high branch aes prevents high probability trails existing multiple rounds fact aes cipher would immune differential linear attacks much weaker non-linear function incredibly high branch active s-box count 25 4r means 8 rounds attack involves fewer 50 non-linear transforms meaning probability success exceed pr attack ≤ pr best attack s-box example current s-box aes emits fixed differential probability higher 4/256 2 far lower required threshold 2 128-bit block cipher would allowed room efficient s-box even 16-uniform probability attack would still 2 exist bijections even sized inputs/outputs 2-uniformity exist odd fields gf 2 using either cubing inversion exponents used well instance x x odd binary field immune differential linear cryptanalysis part misty designs use 7- 9-bit functions 16-bit non-linear function functions gain immunity differential linear attacks lose algebraic attacks possible describe solve via sat solver part aes instance affine mapping inversion
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Computer security
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snowden files snowden files inside story world wanted man 2014 book luke harding published vintage books greg miller washington post described book first single-book account edward snowden 2013 leaking national security agency nsa documents however miller commented british perspective book overlooks significant u.s. developments underplays important work done journalists including barton gellman washington post greg miller concluded harding delivered clearly written captivating account snowden leaks aftermath succeeding beyond basic ambition arrive bookstores first book received positive reviews guardian london review books called super-readable thrillerish account events surrounding reporting documents michiko kakutani new york times wrote book reads like le carré novel crossed something kafka conversely daily telegraph david blair wrote harding story crackles verve complexity nuance banished particular real dilemmas intelligence work ignored snowden files initially criticised snowden associate journalist glenn greenwald read extracts harding book later reading whole book conceded criticise snowden february 14 2014 greenwald told financial times purporting tell inside story edward snowden written someone never met even spoken edward snowden luke came talked half day without realising trying get write book cut interview realised financial times since amended article stating harding insists spoke greenwald rio made clear research book snowden wikileaks founder snowden backer julian assange—subject 2011 book coauthored luke harding david leigh assange condemned—harshly criticized snowden files author calling book walloping fraud written frauds praised frauds assange stated disappointing thing snowden files exploitative existed understand pressures facing print journalism need diversify revenue order cross-subsidize investigative journalism investigative journalism involves able develop relationships trust sources snowden files along fictionalized time octopus snowden russian lawyer anatoly kucherena forms basis oliver stone film snowden 2016
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Computer security
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security descriptor security descriptors data structures security information securable windows objects objects identified unique name security descriptors associated named objects including files folders shares registry keys processes threads named pipes services job objects resources security descriptors contain discretionary access control lists dacls contain access control entries aces grant deny access trustees users groups also contain system access control list sacls control auditing object access aces may explicitly applied object inherited parent object order aces acl important access denied aces appearing higher order aces grant access security descriptors also contain object owner mandatory integrity control implemented new type ace security descriptor files folder permissions edited various tools including windows explorer wmi command line tools like cacls xcacls icacls subinacl freeware win32 console fileacl free software utility setacl utilities edit security descriptor user needs write_dac permissions object permission usually delegated default administrators object owner ntfs uses set 14 12 older systems permissions files folders form acl stored security descriptors following table summarizes system permissions individual rows obscured using different names abbreviations various programs see icacls cacls columns well number levels permission mappings like generic access rights columns gr ge gw ga table generic_read generic_execute generic_write generic_all respectively standard access rights special permissions mapped permissions files folders
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Operating systems
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broadcast radiation broadcast radiation accumulation broadcast multicast traffic computer network extreme amounts broadcast traffic constitute broadcast storm broadcast storm consume sufficient network resources render network unable transport normal traffic packet induces storm occasionally nicknamed chernobyl packet commonly cause switching loop ethernet wiring topology i.e two paths exist end stations broadcasts multicasts forwarded switches every port switch switches repeatedly rebroadcast broadcast messages flood network since layer 2 header support time live ttl value frame sent looped topology loop forever cases broadcast storm instigated purpose denial service dos using one packet amplification attacks smurf attack fraggle attack smurf sends large amount icmp echo requests ping traffic broadcast address icmp echo packet containing spoof source address victim host spoofed packet arrives destination network hosts network reply spoofed address initial echo request multiplied number hosts network generates storm replies victim host tying network bandwidth using cpu resources possibly crashing victim wireless networks disassociation packet spoofed source wireless access point sent broadcast address generate disassociation broadcast dos attack mobile ad hoc network manet route request rreq packets usually broadcast discover new routes rreq packets may cause broadcast storms compete channel data packets one approach alleviate broadcast storm problem inhibit hosts rebroadcasting reduce redundancy thus contention collision
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Computer security
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fluhrer mantin shamir attack cryptography fluhrer mantin shamir attack stream cipher attack widely used rc4 stream cipher attack allows attacker recover key rc4 encrypted stream large number messages stream fluhrer mantin shamir attack applies specific key derivation methods apply general rc4-based ssl tls since ssl generates encryption keys uses rc4 hashing meaning different ssl sessions unrelated keys however closely related bar mitzvah attack based research revealed 2015 exploit cases weak keys generated ssl keying process fluhrer mantin shamir fms attack published 2001 paper weaknesses key scheduling algorithm rc4 takes advantage weakness rc4 key scheduling algorithm reconstruct key encrypted messages fms attack gained popularity network attack tools including airsnort weplab aircrack use recover key used wep protected wireless networks discussion use rc4 key scheduling algorithm ksa following pseudo-random generation algorithm prga also used basis fms attack lies use weak initialization vectors ivs used rc4 rc4 encrypts one byte time keystream output prga rc4 uses key initialize state machine via ksa continuously modifies state generates new byte keystream new state theoretically key stream functions random one-time pad pseudo-random number generator controls output step certain ivs attacker knowing first byte keystream first bytes key derive 1 th byte key due weakness prng used generate keystream first byte plaintext comes wep snap header attacker assume derive first byte keystream b ⊕ 0x aa snap header almost always 0xaa needs iv form 3 n − 1 x key index origin 0 element value space n 256 since 8 bits make byte x start attacker needs ivs 3 255 x wep uses 24-bit ivs making value one byte long start attacker utilizes iv first 3 elements k fills s-box sequential values 0 n rc4 initializing s-box known k performs first 3 iterations ksa begin initializing s-box third step attacker possibly definitely derive fourth byte key using keystream output computing − j − mod n k value 3 step point attacker yet fourth byte key algorithm regenerate next byte key generates possible value key collecting multiple messages—for example wep packets—and repeating steps attacker generate number different possible values correct value appears significantly frequently attacker determine value key recognizing value selecting next byte point start attack fifth byte key although attacker attack words key order store messages later sequential attack later words knows earlier words needs messages weak ivs discard others process gather large number messages attack entire key fact store short portion beginning messages enough carry attack far word key iv allow attack
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Computer security
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list webos devices
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Operating systems
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luna luna computer product line omron tateishi electric late 1980s early 1990s luna 20mhz/m68030 desktop computer netbsd supported luna since 1.4.2 released 2000 later omron luna 88k available two models dt8840 td8860 1-4 25 mhz 88100 cpus 16 mb ram native operating system cmu mach 2.5 omron unios
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Computer architecture
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lisp small pieces lisp small pieces cambridge university press 1996 paperback edition december 4 2003 translated kathleen callaway book christian queinnec lisp scheme related dialects interpretation semantics compilation contains code 11 interpreters 2 compilers english title kind recursive acronym lisp small pieces originally published french interéditions title les langages lisp revised edition published paracamplus bears title principes d'implantation de scheme et lisp another acronym based cover layout orders title following list lisp implementation scheme principes book available english cambridge university press french version available le monde en tique parisian bookstore
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Programming language topics
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iland iland internet solutions provides hosted cloud infrastructure service production business applications disaster recovery business continuity testing development software service enablement independent software vendors iland also provides traditional colocation hybrid cloud solutions founded 1995 iland provides services high availability hubs specifically designed cloud infrastructure boston washington d.c. houston los angeles dallas manchester london amsterdam singapore melbourne sydney iland premier-level partner vmware service provider program vspp iland global cloud service provider secure compliant hosting infrastructure iaas disaster recovery draas backup service baas headquartered houston texas london uk iland delivers cloud services data centers throughout americas europe asia australia iland provides cloud-based disaster recovery business continuity services solution iland continuity cloud includes data replication targets enterprise data standby resources activated disasters restore data application business services services include iland workforce cloud integrates desktop virtualization company overall business continuity disaster recovery plan iland saas cloud provides cloud environment specifically software services saas providers iland hybrid cloud merges virtual cloud physical colocated servers custom enterprise configurations iland enterprise cloud provides cloud environment production business systems iland replication-as-a-service raas provides data replication service dell equallogic customers iland cloud environment
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Distributed computing architecture
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lightning memory-mapped database lightning memory-mapped database lmdb software library provides high-performance embedded transactional database form key-value store lmdb written c api bindings several programming languages lmdb stores arbitrary key/data pairs byte arrays range-based search capability supports multiple data items single key special mode appending records end database mdb_append gives dramatic write performance increase similar stores lmdb relational database strictly key-value store like berkeley db dbm lmdb may also used concurrently multi-threaded multi-processing environment read performance scaling linearly design lmdb databases may one writer time however unlike many similar key-value databases write transactions block readers readers block writers lmdb also unusual multiple applications system may simultaneously open use lmdb store means scale performance also lmdb require transaction log thereby increasing write performance needing write data twice maintains data integrity inherently design lmdb design first discussed 2009 post openldap developer mailing list context exploring solutions cache management difficulty caused project dependence berkeley db specific goal replace multiple layers configuration caching inherent berkeley db design single automatically managed cache control host operating system development subsequently began initially fork similar implementation openbsd ldapd project first publicly available version appeared openldap source repository june 2011 project known mdb november 2012 renamed order avoid conflicts existing software internally lmdb uses b+ tree data structures efficiency design small footprint unintended side-effect providing good write performance well lmdb api similar berkeley db dbm lmdb treats computer memory single address space shared across multiple processes threads using shared memory copy-on-write semantics known historically single-level store due former modern computing architectures 32-bit memory address space limitations imposes hard limit 4 gb size database using techniques effectiveness technique directly mapping database single-level store strictly limited however today 64-bit processors mostly implement 48-bit address spaces giving access 47-bit addresses 128 terabytes database size making databases using shared memory useful real-world applications specific noteworthy technical features lmdb lmdb employs multiversion concurrency control mvcc allows multiple threads within multiple processes coordinate simultaneous access database readers scale linearly design write transactions globally serialized via mutex read-only transactions operate parallel including presence write transaction entirely wait free except first read-only transaction thread thread reading database gains ownership element shared memory array may update indicate within transaction writers scan array determine oldest database version transaction must preserve without requiring direct synchronization active readers 2011 google published software allowed users generate micro-benchmarks comparing leveldb performance sqlite kyoto cabinet different scenarios 2012 symas added support lmdb berkeley db made updated benchmarking software publicly available resulting benchmarks showed lmdb outperformed databases read batch write operations sqlite lmdb excelled write operations particularly synchronous/transactional writes benchmarks showed underlying filesystem big influence performance jfs external journal performs well especially compared modern systems like btrfs zfs zimbra tested back-mdb vs back-hdb performance openldap lmdb clearly outperforming bdb based back-hdb many openldap users observed similar benefits since initial benchmarking work done 2012 multiple follow-on tests conducted additional database engines in-memory on-disk workloads characterizing performance across multiple cpus record sizes tests show lmdb performance unmatched in-memory workloads excels disk-bound read workloads well disk-bound write workloads using large record sizes benchmark driver code subsequently published github expanded database coverage lmdb designed start resist data loss face system application crashes copy-on-write approach never overwrites currently-in-use data avoiding overwrites means structure disk/storage always valid application system crashes never leave database corrupted state default mode worst crash lose data last not-yet-committed write transaction even asynchronous modes enabled os catastrophic failure hardware power-loss event rather merely application crash could potentially result data corruption two academic papers usenix osdi symposium covered failure modes db engines including lmdb sudden power loss system crash paper pillai et al. find failure lmdb would occur real-world file systems considered single failure identified study lmdb relates hypothetical file systems mai zheng et al paper claims point failures lmdb conclusion depends whether fsync fdatasync utilised using fsync ameliorates problem selection fsync fdatasync compile-time switch default behavior current gnu/linux builds lmdb default macos *bsd android windows default gnu/linux builds lmdb therefore ones vulnerable problem discovered zhengmai researchers however lmdb may simply rebuilt gnu/linux users utilise fsync instead june 2013 oracle changed license berkeley db related project sleepycat license affero general public license thus restricting use wide variety applications caused debian project exclude library 6.0 onwards also criticized license friendly commercial redistributors discussion sparked whether licensing change could happen lmdb author howard chu made clear lmdb part openldap project bsd style license joined stay like copyright transferred anybody checking would make similar move like oracle impossible berkeley db license issue caused major gnu/linux distributions debian completely phase use berkeley db preference lmdb wrappers several programming languages c++ java python lua go ruby objective c javascript c perl php tcl common lisp complete list wrappers may found main web site howard chu ported sqlite 3.7.7.1 use lmdb instead original b-tree code calling end result sqlightning one cited insert test 1000 records 20 times faster original sqlite b-tree implementation lmdb available backing store open source projects including cyrus sasl heimdal kerberos opendkim also available nosql projects like memcachedb mapkeeper lmdb used make in-memory store redis persist data disk existing back-end redis showed pathological behaviour rare cases replacement sought baroque api lmdb criticized though forcing lot coding get simple things done however performance reliability testing considerably better alternative back-end stores tried independent third-party software developer utilised python bindings lmdb high-performance environment published prominent technical news site slashdot system managed successfully sustain 200,000 simultaneous read write delete operations per second total 600,000 database operations per second up-to-date list applications using lmdb maintained main web site many popular free software projects distribute include support lmdb often primary sole storage mechanism lmdb makes unusual novel use well-known computer science techniques copy-on-write semantics b+ trees provide atomicity reliability guarantees well performance hard accept given library relative simplicity similar key-value store database offers guarantees overall performance even though authors explicitly state presentations lmdb read-optimised write-optimised additionally lmdb primarily developed use openldap developers focussed mainly development maintenance openldap lmdb per se developers limited time spent presenting first benchmark results therefore criticized stating limitations giving silver bullet impression adequate address engineers attitude pointed concerns raised however later adequately addressed reviewer satisfaction key developer behind lmdb presentation spark database developers dissecting code in-depth understand works reviews run brief in-depth database developer oren eini wrote 12-part series articles analysis lmdb beginning july 9 2013 conclusion lines impressive codebase ... dearly needs love mainly long methods code duplication review conducted .net developer former experience c concluded august 22 2013 beyond issues code implementation really quite brilliant way lmdb manages pack much functionality things quite impressive ... learned quite lot project frustrating annoying fascinating experience multiple reviews cover lmdb various languages including chinese
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Databases
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belenix belenix discontinued operating system distribution built using opensolaris source base used live cd well installed hard disk information provided belenix website may appear currently belenix compiled 32-bit execution i586/pentium op-code based compounded lack clarity belenix site whether belenix distribution supports true 64-bit i.e. x86-64/amd64 solaris kernel userland however oblique references belenix team members indicated belenix 0.7 live cd contains 32-bit 64-bit installation files initially developed live cd along lines knoppix showcase opensolaris technologies belenix went become initial base sun opensolaris distribution number technologies pioneered belenix project gone become full projects right within opensolaris ecosystem belenix focused using kde desktop environment although xfce also supported since beginning distribution upcoming release also include first-class support gnome belenix dev team focuses technology innovation aims working communities including opensolaris based distros milax nexenta os schillix name logo references celtic god light belenus belenix aims latest stable revisions software packages continuously pushed package repository aim mind however many cases bleeding-edge software pushed help validate try new features due reasons belenix also includes lot third-party drivers may found official opensolaris distribution sun focus belenix developer desktop also stable scalable enough work workstation development server environment mainly due quality underlying opensolaris kernel userland environment belenix thus also first-class opensolaris development environment completely self-hosting every package included belenix built belenix including opensolaris kernel belenix aims easy-to-use distribution gently exposes power opensolaris live cd format makes opensolaris easily approachable boots within two three minutes cd-rom also aims encourage innovation bringing new features usability enhancements increasing community participation announcement opensolaris project belenix started private project sun employees working sun india engineering centre bangalore india year 2005 aim something along lines knoppix showcase opensolaris end users weeks time iso image ready people make use period time belenix developed grew popularity non-sun contributors also joined effort developing foss community project belenix first opensolaris distribution bundle complete working xorg x11 gui environment years number critical innovations sprung belenix project later incorporated opensolaris distributions sun fact first beta release sun opensolaris distro largely based belenix belenix second opensolaris distribution appear schillix first provide auto-configuring xorg based gui introduced various missing technologies opensolaris important innovations include project indiana leveraged technologies served starting point taking technologies developed indiana account future focus belenix set evolve grow source-level indiana derivate focus kde desktop make fully featured functional opensolaris distro based kde check livecd features timeline references see chronological account belenix development till release opensolaris distro sun 2008 belenix team aims ensure packages co-exist system ensuring latest versions package built latest compilers result belenix far kde 3.5.9 built gcc 3.4.3 newer packages including kde4 increasingly built gcc 4.4 packages especially gnome components derived jds project built sun studio 12 actively migrated gcc 4.4 team aims eventually belenix built completely foss toolchain gcc belenix far positioned kde distribution also providing xfce upcoming releases also provide gnome belenix today uses caiman installer libraries used sun opensolaris distro going forward plans re-implement installer gui qt4 still using underlying caiman installer libraries belenix team presently continues use svr4 packaging solaris provided date team intend use ips present state due various technical reasons considering alternatives including deb format rpm5 format along smart package manager
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Operating systems
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line code telecommunication line code pattern voltage current photons used represent digital data transmitted transmission line repertoire signals usually called constrained code data storage systems signals prone error others conveyed communication channel physics communication storage medium constrains repertoire signals used reliably common line encodings unipolar polar bipolar manchester code line coding signal put physical communication channel either transmission medium data storage medium common physical channels common binary line codes include line code advantages disadvantages line codes chosen meet one following criteria long-distance communication channels reliably transport dc component dc component also called disparity bias dc coefficient disparity bit pattern difference number one bits vs number zero bits running disparity running total disparity previously transmitted bits simplest possible line code unipolar gives many errors systems unbounded dc component line codes eliminate dc component codes called dc-balanced zero-dc dc-free three ways eliminating dc component bipolar line codes two polarities generally implemented rz radix three since three distinct output levels negative positive zero one principle advantages type code completely eliminate dc component important signal must pass transformer long transmission line unfortunately several long-distance communication channels polarity ambiguity polarity-insensitive line codes compensate channels three ways providing unambiguous reception 0 1 bits channels reliable clock recovery receiver maximum run length constraint may imposed generated channel sequence i.e. maximum number consecutive ones zeros bounded reasonable number clock period recovered observing transitions received sequence maximum run length guarantees clock recovery sequences without constraint could seriously hamper detection quality run-length limited rll coding line coding technique used send arbitrary data communications channel bandwidth limits rll codes defined four main parameters n k first two n refer rate code remaining two specify minimal maximal k number zeroes consecutive ones used telecommunication storage systems move medium past fixed recording head specifically rll bounds length stretches runs repeated bits signal change runs long clock recovery difficult short high frequencies might attenuated communications channel modulating data rll reduces timing uncertainty decoding stored data would lead possible erroneous insertion removal bits reading data back mechanism ensures boundaries bits always accurately found preventing bit slip efficiently using media reliably store maximal amount data given space early disk drives used simple encoding schemes rll 0,1 fm code followed rll 1,3 mfm code widely used hard disk drives mid-1980s still used digital optical discs cd dvd md hi-md blu-ray using efm efmplus codes higher density rll 2,7 rll 1,7 codes became de facto industry standard hard disks early 1990s line coding make possible receiver synchronize phase received signal synchronization ideal signal decoded optimal differences amplitude various digits symbols used line code increase error probability received data biphase line codes require least one transition per bit time makes easier synchronize transceivers detect errors however baud rate greater nrz codes also preferred line code structure enable error detection note line-coded signal signal produced terminal may differ thus requiring translation line code typically reflect technical requirements transmission medium optical fiber shielded twisted pair requirements unique medium one different behavior related interference distortion capacitance loss amplitude optical line codes
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Internet protocols
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conference email anti-spam conference email anti-spam ceas annual scientific conference sponsored microsoft subjects relating email use abuse latter commonly known spam ceas hosts concurrent open competition spam filters known ceas live spam filter challenge first conference held july 30–31 2004 2008 conference site always california either mountain view stanford university web site also apparently hosted stanford university sixth conference ceas held mountain view california seventh conference held redmond washington
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Computer security
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bacula bacula open-source enterprise-level computer backup system heterogeneous networks designed automate backup tasks often required intervention systems administrator computer operator bacula supports linux unix windows macos backup clients range professional backup devices including tape libraries administrators operators configure system via command line console gui web interface back-end catalog information stored mysql postgresql sqlite bacula set computer programs managing backup recovery verification computer data across network—providing backup solution mixed operating system environments bacula open-source released agpl version 3 license exceptions permit linking openssl distributing windows binaries bacula available dual license see multi-licensing agplv3 proprietary license several entities offer commercial support agpl bacula community version bacula systems sells various levels annual support contracts bacula enterprise edition contains various non-gpl components developed in-house 2015 bacula systems named top 20 promising data center solution providers cio review common dual-license software components developed bacula enterprise edition released bacula community edition period exclusivity proprietary version since april 2002 bacula 2 million downloads makes downloaded open-source backup program bacula features include client software executed file daemon running bacula client supports multiple operating systems default bacula differential incremental backups based system time stamps consequently move files existing directory move whole directory backup fileset full backup files may backed incremental save may old dates must explicitly update date/time stamp moved files bacula versions starting 3.0 later support accurate backup option addresses issue without requiring modification files timestamps feature always used accurate state filesystem important criteria applied configurable i.e inode comparisons modification times md5/sha1 signatures 2011 graham keeling former bacula community developer released friendly fork bacula february 2013 former bacula community developer several free software users released bareos fork bacula
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Computer security
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wire protocol computer networking wire protocol refers way getting data point point wire protocol needed one application interoperate generally refers protocols higher physical layer contrast transport protocols transport level like tcp udp term wire protocol used describe common way represent information application level refers common application layer protocol common object semantic applications representation application level needs common infoset e.g xml data binding using e.g common encoding scheme like xsd wire protocol may either text-based binary protocol although important architectural decision separate matter distinction wire protocols programmatic apis electronics wire protocol mechanism used transmit data one point another wire protocol provides means interoperation one applications network often refer distributed object protocols use applications designed work together name suggests distributed object protocols run different processes one several computers connected network wire protocols provide means program running one operating system communicate program running operating system using internet interconnect multiple platforms language-independent allowing communication programs written different languages examples wire protocols include
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Internet protocols
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quel query languages quel relational database query language based tuple relational calculus similarities sql created part ingres dbms effort university california berkeley based codd earlier suggested implemented data sub-language alpha quel used short time products based freely available ingres source code notably implementation called postquel supported postgres oracle db2 gained market share early 1980s companies supporting quel moved sql instead quel continues available part ingres dbms although quel-specific language enhancements added many years quel statements always defined tuple variables used limit queries return result sets consider example taken one first original ingres papers equivalent sql statement sample simple session creates table inserts row retrieves modifies data inside finally deletes row added assuming name unique field another feature quel built-in system moving records en-masse system consider command creates comma-delimited file records student table d1 indicates delimiter opposed data type changing codice_1 codice_2 reverses process similar commands available many sql systems usually external tools opposed internal sql language makes unavailable stored procedures quel extremely powerful aggregation capability aggregates nested different aggregates independent by-lists and/or restriction clauses example example illustrates one arguably less desirable quirks quel namely string comparisons potentially pattern matches codice_3 matches y.str values starting ii
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Databases
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edward j. barrett rear admiral edward joseph barrett born august 14 1943 flag officer united states coast guard serving chief systems united states coast guard serving 1966 1999 grandfather former nsa contractor edward snowden barrett born city poughkeepsie state new york united states august 14 1943 graduated united states coast guard academy 1966 barrett completed naval flight training nas pensacola florida 1968 1995 barrett inducted united states coast guard academy hall fame admiral barrett testified congress several times regards narcotics explosives ship scanning technology barrett father elizabeth wendy snowden jennifer barrett julie barret former father law chief warrant officer aviation maintenance 4 lonnie snowden ret uscg
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Computer security
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gfs2 computing global file system 2 gfs2 shared-disk file system linux computer clusters gfs2 differs distributed file systems afs coda intermezzo glusterfs gfs2 allows nodes direct concurrent access shared block storage addition gfs gfs2 also used local filesystem gfs disconnected operating-mode client server roles nodes gfs cluster function peers using gfs cluster requires hardware allow access shared storage lock manager control access storage lock manager operates separate module thus gfs gfs2 use distributed lock manager dlm cluster configurations nolock lock manager local filesystems older versions gfs also support gulm server-based lock manager implements redundancy via failover gfs gfs2 free software distributed terms gnu general public license development gfs began 1995 originally developed university minnesota professor matthew o'keefe group students originally written sgi irix operating system 1998 ported linux since open source code provided convenient development platform late 1999/early 2000 made way sistina software lived time open-source project 2001 sistina made choice make gfs proprietary product developers forked opengfs last public release gfs enhanced include updates allowing work opendlm opengfs opendlm became defunct since red hat purchased sistina december 2003 released gfs many cluster-infrastructure pieces gpl late june 2004 red hat subsequently financed development geared towards bug-fixing stabilization development gfs2 derives gfs included along distributed lock manager shared gfs linux 2.6.19 red hat enterprise linux 5.2 included gfs2 kernel module evaluation purposes 5.3 update gfs2 became part kernel package gfs forms part fedora red hat enterprise linux 5.3 upwards associated centos linux distributions users purchase commercial support run gfs fully supported top red hat enterprise linux since red hat enterprise linux version 5.3 red hat enterprise linux advanced platform included support gfs additional cost following list summarizes version numbers major features introduced design gfs gfs2 targets san-like environments although possible use single node filesystem full feature-set requires san take form iscsi fibrechannel aoe device presented linux block device shared number nodes example drbd device dlm requires ip based network communicate normally ethernet many possible solutions depending upon choice san may possible combine normal practice involves separate networks dlm storage gfs requires fencing hardware kind requirement cluster infrastructure rather gfs/gfs2 required multi-node clusters usual options include power switches remote access controllers e.g drac ipmi ilo fencing used ensure node cluster believes failed suddenly start working another node recovering journal failed node also optionally restart failed node automatically recovery complete although designers gfs/gfs2 aimed emulate local filesystem closely number differences aware due existing filesystem interfaces allowing passing information relating cluster stem difficulty implementing features efficiently clustered manner example main difference one shared similar cluster filesystems cache control mechanism known glocks pronounced gee-locks gfs/gfs2 effect across whole cluster inode filesystem two glocks associated one called iopen glock keeps track processes inode open inode glock controls cache relating inode glock four states un unlocked sh shared – read lock df deferred – read lock incompatible sh ex exclusive four modes maps directly dlm lock mode ex mode inode allowed cache data metadata might dirty i.e waiting write back filesystem sh mode inode cache data metadata must dirty df mode inode allowed cache metadata must dirty df mode used direct i/o un mode inode must cache metadata order operations change inode data metadata interfere ex lock used means certain operations create/unlink files directory writes file general restricted one node cluster course operations multiple nodes work expected due requirement flush caches frequently efficient single frequently asked question gfs/gfs2 performance performance poor email servers solution break mail spool separate directories try keep far possible node reading writing private set directories gfs gfs2 journaled file systems gfs2 supports similar set journaling modes ext3 data=writeback mode metadata journaled mode supported gfs however possible turn journaling individual data-files zero size journaled files gfs number restrictions placed upon support mmap sendfile system calls also use different on-disk format regular files also inherit-journal attribute set directory causes files sub-directories created within directory journal inherit-journal respectively flag set used instead data=journal mount option ext3 supports gfs/gfs2 gfs2 also supports data=ordered mode similar data=writeback except dirty data synced journal flush completed ensures blocks added inode content synced back disk metadata updated record new size thus prevents uninitialised blocks appearing file node failure conditions default journaling mode data=ordered match ext3 default gfs2 yet support data=journal mode unlike gfs use on-disk format regular journaled files also supports journaled inherit-journal attributes gfs2 also relaxes restrictions file may journaled attribute changed time file open also ext3 performance reasons node gfs gfs2 journal gfs journals disk extents gfs2 journals regular files number nodes may mount filesystem one time limited number available journals gfs2 adds number new features gfs summary features already mentioned boxes right page gfs2 designed upgrading gfs would simple procedure end on-disk structure remained gfs including big-endian byte ordering differences though journaling systems gfs gfs2 compatible upgrading possible means tool gfs2_convert run filesystem off-line update metadata spare blocks gfs journals used create small per_node files required gfs2 update process data remains place gfs2 meta filesystem filesystem right alternate root main filesystem although behaves like normal filesystem contents various system files used gfs2 normally users need ever look gfs2 utilities mount unmount meta filesystem required behind scenes
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Computer file systems
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secure design secure design software engineering means software designed foundation secure malicious practices taken granted care taken minimize impact anticipation security vulnerabilities security vulnerability discovered invalid user input closely related practice using good software design domain-driven design cloud native way increase security reducing risk vulnerability-opening mistakes—even though design principles used originally conceived security purposes generally designs work well rely secret often secrecy reduces number attackers demotivating subset threat population logic increase complexity attacker increased attacker effort compromise target technique implies reduced inherent risks virtually infinite set threat actors techniques applied time cause secrecy methods fail mandatory proper security usually means everyone allowed know understand design secure advantage many people looking computer code improves odds flaws found sooner see linus law attackers also obtain code makes easier find vulnerabilities well also important everything works fewest privileges possible see principle least privilege example web server runs administrative user root admin privilege remove files users belong flaw program could put entire system risk whereas web server runs inside isolated environment privileges required network filesystem functions compromise system runs unless security around also flawed many things especially input distrusted secure design fault-tolerant program could even distrust internals two examples insecure design allowing buffer overflows format string vulnerabilities following c program demonstrates flaws gets function c standard library stop writing bytes codice_1 reads newline character eof typing 99 characters prompt constitutes buffer overflow allocating 100 characters codice_1 assumption almost given name user longer 99 characters n't prevent user actually typing 99 characters lead arbitrary machine code execution second flaw program tries print input passing directly codice_3 function function prints first argument replacing conversion specifications et cetera sequentially arguments call stack needed thus malicious user entered instead name program would attempt print non-existent integer value undefined behavior would occur related mistake web programming online script validate parameters example consider script fetches article taking filename read script parsed script might use following hypothetical url retrieve article dog food script input checking instead trusting filename always valid malicious user could forge url retrieve configuration files webserver depending script may expose /etc/passwd file unix-like systems contains among others user ids login names home directory paths shells see sql injection similar attack server/client architectures program side may authorised client client server may authorised server even man-in-the-middle attack could compromise communications often easiest way break security client/server system go head security mechanisms instead go around man middle attack simple example use collect details impersonate user important consider encryption hashing security mechanisms design ensure information collected potential attacker wo n't allow access another key feature client-server security design good coding practices example following known software design structure client broker help designing well-built structure solid foundation furthermore software modified future even important follows logical foundation separation client server programmer comes clearly understand dynamics program may end adding changing something add security flaw even best design always possibility better standardized design less chance occurring
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Computer security
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carbon black company carbon black inc. formerly bit9 inc. cybersecurity company based waltham massachusetts company develops cloud-native endpoint security software designed detect malicious behavior help prevent malicious files attacking organization company leverages technology known predictive security cloud psc big data analytics cloud platform analyzes customers ’ unfiltered data threats company approximately 100 partners including ibm vmware partners account approximately 125 product integrations according s-1 filing sec carbon black currently 5,600-plus customers including approximately one third fortune 100 4 may 2018 company joined public markets listing cblk nasdaq exchange part ipo carbon black raised approximately 152 million valuation 1.25 billion prior ipo firm raised 190m investors including kleiner perkins highland capital sequoia accomplice blackstone carbon black founded bit9 inc. 2002 todd brennan allen hillery john hanratty company first ceo george kassabgi current ceo patrick morley formerly chief operating officer corel took position 2007 2013 company network broken malicious actors copied private signing key certificate used sign malware february 2014 bit9 acquired start-up security firm carbon black time acquisition company also raised 38.25 million series e funding bringing bit9 ’ total venture capital raised approximately 120 million company acquired objective logistics june 2015 august 2015 carbon black announced acquired data analytics firm visitrend would open technology development center downtown boston month later company announced would partner secureworks ernst young kroll trustwave rapid7 provide managed security incident response services company changed name bit9 inc carbon black inc. february 1 2016 july 2016 carbon black announced acquired next-generation antivirus provider confer undisclosed sum prior deal confer raised 25m venture funding 50 employees according wall street journal deal valued 100m
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Computer security
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davinci software davinci development tool used create html5 mobile applications media content includes jquery framework javascript library used developers designers create web applications used mobile devices user experience similar native applications business applications games rich media content html5 multi-media magazines advertisements animation may produced tool davinci based standard web technology including html5 css3 javascript davinci composed davinci studio davinci animator handle application programming ui design respectively tool wysiwyg see get authoring environment users may drag drop components build applications design web content open source libraries knockout jsview/jsrender impress.js turn.js included tool open source frameworks may also integrated model view controller mvc data binding javascript may handled davinci ’ data-set editor view components model data may visually bound allows users create web applications server integrated ui components without coding davinci also includes n-screen editor automatically applies designs functions screen size various devices smartphones tablet pcs smarttv davinci worked closely jquery foundation presenting first jquery conference asian district november 12 2012 seoul south korea davinci used tool demonstrate application development techniques conference
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Programming language topics
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roboto roboto neo-grotesque sans-serif typeface family developed google system font mobile operating system android released 2011 android 4.0 ice cream sandwich google developed font modern yet approachable emotional entire font family licensed apache license 2014 roboto redesigned android 5.0 lollipop roboto default font android since 2013 google services google+ google play youtube google maps mobile google search 2017 roboto used lcd countdown clocks new york city subway b division lines roboto bold default font unreal engine 4 kodi roboto condensed used display information european versions nintendo switch packaging including physical releases games font designed entirely in-house christian robertson previously released expanded ubuntu-title font personal type foundry betatype font officially made available free download january 12 2012 newly launched android design website compared android previous system font humanist sans-serif droid roboto belongs neo-grotesque genre sans-serif typefaces includes thin light regular medium bold black weights matching oblique styles rather true italics also includes condensed styles light regular bold also matching oblique designs 2014 matias duarte announced google i/o roboto significantly redesigned android 5.0 lollipop punctuation marks tittles lowercase j changed square rounded roboto received variable reviews release joshua topolsky editor-in-chief technology news media network verge describes font clean modern overly futuristic – science fiction font however typography commentator stephen coles typographica.org called initial release roboto “ four-headed frankenfont ” describing “ hodgepodge ” different typographic styles work well together type design professionals called obvious errors accented glyphs john gruber called font helvetica ripoff roboto supports latin greek partial cyrillic scripts android noto font used languages supported roboto including chinese simplified traditional japanese korean thai hindi roboto slab slab serif font based roboto introduced march 2013 default font google note-taking service google keep font changed sans-serif roboto 2018 available four weights thin light regular bold however oblique versions released roboto mono monospace font based roboto available five weights thin light regular medium bold oblique stylings weight heebo extension roboto includes hebrew characters
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Operating systems
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list ios devices list comparison devices designed marketed apple inc. run unix-like operating system named ios ipados often colloquially referred simply idevices devices include iphone ipod touch design similar iphone cellular radio cell phone hardware ipad three devices function digital audio portable media players internet clients apple tv runs tvos set-top box streaming media local sources certain internet services connected television set screen 1.35 billion ios devices sold worldwide march 2015 operating system ios devices updated itunes ios 5 later using over-the-air ota updates major version ios tends released every time new type iphone launched usually year minor changes throughout year needed updates free ios devices although ipod touch users formerly required pay update apple upgrades products hardware periodically approximately yearly source second third generation apple tv run unnamed operating system derived ios fourth subsequent generations apple tv run ios-based tvos first generation ran modified version mac os x tiger instead ios apple runs tests pre-production units determine battery life however purported maximums actual user experiences vary numbers hours unless specified apple increased storage capacity devices time units available given storage capacity indicated table indicates highest supported versions ios available generation ios devices beta versions may listed support discontinued older devices 3½-inch display introduced original iphone almost unchanged models 2010 ipad larger display also uses different aspect ratio resolution iphone 4 iphone 4s fourth generation ipod touch keep physical dimensions prior models double resolution dimensions thereby quadrupling number pixels amount space iphone 5 first departure traditional iphone ipod touch screen size increasing 3.5 4 resolution increased include extra screen space iphone 6 iphone 6 plus second departure traditional iphone ipod touch screen size increasing screen sizes 4 4.7 5.5 respectively increased resolution include extra screen space note hardware reviewers commented benchmark results comparable cpu/socs architecture due software codes optimization
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Operating systems
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distributed object distributed computing distributed objects objects sense object-oriented programming distributed across different address spaces either different processes computer even multiple computers connected via network work together sharing data invoking methods often involves location transparency remote objects appear local objects main method distributed object communication remote method invocation generally message-passing one object sends message another object remote machine process perform task results sent back calling object distributed objects popular late 1990s early 2000s since fallen favor term may also generally refer one extensions basic object concept used context distributed computing replicated objects live distributed objects see also internet protocol suite local distributed objects differ many respects rpc facilities cross platform serialization protocol cap n proto amount distributed object protocol distributed object method calls executed chained single network request needs interface references/capabilities distributed objects implemented objective-c using cocoa api nsconnection class supporting objects distributed objects used java rmi corba lets one build distributed mixed object systems dcom framework distributed objects microsoft platform ddobjects framework distributed objects using borland delphi jt framework distributed components using messaging paradigm javaspaces sun specification distributed shared memory space based pyro framework distributed objects using python programming language distributed ruby drb framework distributed objects using ruby programming language
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Distributed computing architecture
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trueimage trueimage postscript-compatible interpreter clone originally developed cal bauer bauer enterprises sold microsoft 1989 microsoft subsequently cross-licensed trueimage apple computer exchange truetype license many delays microsoft finally delivered version 1.0 trueimage apple apple announced would licensing postscript level 2 adobe systems months later apple tried build one product trueimage trueimage products ever released company however trueimage used variety laser printers abaton okidata lasermaster mid-1990s limited success
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Programming language topics
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personal broadcasting personal broadcasting particular type broadcasting individual broadcaster creates content webcam camcorder transmits internet broadcasting personal context production also feel content type broadcasting individuals editors directors broadcasting personal broadcasting popularly used individuals event holders want broadcast one event audience watch live internet personal broadcasting gives individuals another way interact one another gives brands another way interact customers individual entrepreneurs use personal broadcasting boost brands among young consumers personal broadcasting differs types broadcasting way fixed broadcasting time broadcaster freely choose broadcasting content personal broadcasting limited celebrities public figures produced regular people anybody anywhere time broadcast content free market personal broadcasting allows ordinary individuals broadcast internet rapidly growing personal broadcasting individuals free stream sort broadcast want attract viewers send real-time comments text messages displayed directly across screens broadcaster see respond way viewers watch videos personal broadcasters time share thoughts feelings others live since beginning 2000s personal broadcasting gaining lot interest public become one entertainment options popularity watching video increased demand personal broadcasting initiated rise penetration smartphone equipped high-definition cameras new generation video applications enabled individuals broadcast straight one ’ mobile device whenever like wherever may widespread supply different types broadcasting software including live-streaming applications allowed individuals easily broadcast encouraged popularity personal broadcasting among young generation willing show personal lives online fun fame personal broadcasting lets individuals engaged self-branding turning private public new form mobile self-expression personal broadcasting popularized china republic korea particular despite increasing number personal broadcasting services lacks proper monitoring systems look illicit contents
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Web technology
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gateway-to-gateway protocol gateway-to-gateway protocol ggp obsolete protocol defined routing datagrams internet gateways gateway-to-gateway protocol designed internet protocol ip datagram service similar transmission control protocol tcp user datagram protocol udp however classified internet layer protocol ggp uses minimum hop algorithm measures distance router hops router defined zero hops directly connected networks one hop networks reachable one gateway protocol implements distributed shortest-path methodology therefore requires global convergence routing tables change link connectivity network ggp message field header identifies message type format remaining fields core routers participated ggp core routers controlled central authority routers could interfere exchange
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Internet protocols
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mark cerny mark evan cerny born august 24 1964 american video game designer programmer producer entertainment executive raised san francisco bay area cerny graduated college preparatory school attended uc berkeley president cerny games founded 1998 acts consultant video game industry 2004 recipient lifetime achievement award international game developers association inducted academy interactive arts sciences hall fame 2010 mid 2010s cerny served lead architect producer sony playstation 4 playstation vita video game consoles cerny fan computer programming arcade games started game industry age 17 joined atari 1982 earlier days professional game development teams small member responsible wider range roles today cerny first major success usually cited marble madness age 18 acted designer co-programmer later worked sega japan united states worked various master system genesis releases notably sonic hedgehog 2 cerny vice president president universal interactive studios worked naughty dog crash bandicoot jak daxter series first uncharted game insomniac games spyro dragon ratchet clank resistance series sony experience dos don'ts game industry developed teaching method game development method prefers free-form pre-production stage explores game viability prior full development example advocates first level produced excite players game idea set aside much effort put international game developers association awarded cerny lifetime achievement award game developers choice awards igda 2004 igda stated rare find 'jack-of-all-trades high-level vision great game design act glue adhere pieces together unusual highly effective methodology brought us entertaining games history described master collaborator crash bandicoot spyro dragon games collectively sold 30 million units 2010 13th annual interactive achievement awards mark cerny inducted academy interactive arts sciences hall fame mark cerny closest come modern-day da vinci said joseph olin then-president aias n't restricted single aspect game creation really renaissance man diversely accomplished game designer producer programmer technologist fluent japanese one foremost western experts japanese game market also one top-level independents business dominated institutions february 20 2013 global playstation 4 unveiling event mark cerny revealed console lead architect showed in-game footage game called knack developed console september 21 2013 cerny revealed lead architect playstation vita 2014 hosted career retrospective former sega game designer yu suzuki game developers conference also hosted shenmue postmortem suzuki discussed shenmue iii
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Computer architecture
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middlebox middlebox network appliance computer networking device transforms inspects filters otherwise manipulates traffic purposes packet forwarding common examples middleboxes include firewalls filter unwanted malicious traffic network address translators modify packets source destination addresses dedicated middlebox hardware widely deployed enterprise networks improve network security performance however even home network routers often integrated firewall nat middlebox functionality widespread deployment middleboxes network appliances resulted challenges criticism due poor interaction higher layer protocols lixia zhang jonathan b. postel professor computer science university california los angeles coined term middlebox 1999 following examples commonly deployed middleboxes although widely deployed middleboxes generated technical challenges application development controversy regarding impact middleboxes interfere application functionality restricting preventing end host applications performing properly network address translators present challenge nat devices divide traffic destined public ip address across several receivers connections host internet host behind nat initiated host behind nat nat learns traffic connection belongs local host thus traffic coming internet destined public shared address particular port nat direct traffic appropriate host however connections initiated host internet present nat opportunity learn internal host connection belongs moreover internal host may even know public ip address announce potential clients address connect resolve issue several new protocols proposed common middlebox-induced application challenges include web proxies serving stale date content firewalls rejecting traffic desired ports one criticism middleboxes limit choice transport protocols thus placing limits application service designs middleboxes may filter drop traffic conform expected behaviors new uncommon protocols protocol extensions may filtered middleboxes conversely certain types middlebox assist protocol deployment providing translation new old protocols ipv6 example deployed public endpoints load balancers proxies forms nat backend traffic routed ipv4 ipv6 generally middleboxes considered violate end-to-end principle computer system design
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Computer security
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diskless shared-root cluster diskless shared-root cluster way manage several machines time instead operating system os local disk one image os available server nodes use image ssi cluster single-system image simplest way achieve use nfs server configured host generic boot image ssi cluster nodes pxe dhcp tftp nfs ensure single point failure nfs export boot-image hosted two node cluster architecture diskless computer cluster makes possible separate servers storage array operating system well actual reference data userfiles databases websites stored competitively attached storage system centralized manner server acts cluster node easily exchanged demand additional abstraction layer storage system computing power eases scale infrastructure notably storage capacity computing power network bandwidth scaled independent one another similar technology found vmscluster openvms trucluster tru64 unix open-source implementation diskless shared-root cluster known open-sharedroot
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Distributed computing architecture
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task state segment task state segment tss special structure x86-based computers holds information task used operating system kernel task management specifically following information stored tss information stored specific locations within tss specified ia-32 manuals tss may reside anywhere memory special segment register called task register tr holds segment selector points valid tss segment descriptor resides gdt tss descriptor may reside ldt therefore use tss following must done operating system kernel security purposes tss placed memory accessible kernel tr register 16-bit register holds segment selector tss may loaded ltr instruction ltr privileged instruction acts manner similar segment register loads task register two parts portion visible accessible programmer invisible one automatically loaded tss descriptor tss may contain saved values x86 registers used task switching operating system may load tss values registers new task needs executing hardware task switch iret instruction x86 cpu load saved values tss appropriate registers note modern operating systems windows linux use fields tss implement software task switching note hardware task switch certain fields old tss updated cpu current register contents values new tss read thus tss fields read/write others read-only codice_22 field fact first one read new tss since hardware task switch also switch completely different page table mapping fields especially codice_23 relative new mapping tss contains 16-bit pointer i/o port permissions bitmap current task bitmap usually set operating system task started specifies individual ports program access i/o bitmap bit array port access permissions program permission access port 0 stored corresponding bit index program permission 1 stored tss ’ segment limit less full bitmap missing bits assumed 1 feature operates follows program issues x86 i/o port instruction see x86 instruction listings note byte- word- dword-length versions hardware i/o privilege level iopl check see program access i/o ports cpl program numerically greater iopl program less-privileged iopl specifies program i/o port access ports hardware check i/o permissions bitmap tss see program access specific port instruction relevant bit i/o port permissions bitmap is/are clear program allowed access port instruction allowed execute relevant bit is/are set bit is/are past tss ’ segment limit program access processor generates general protection fault feature allows operating systems grant selective port access user programs tss contains 6 fields specifying new stack pointer privilege level change happens field ss0 contains stack segment selector cpl=0 field esp0/rsp0 contains new esp/rsp value cpl=0 interrupt happens protected 32-bit mode x86 cpu look tss ss0 esp0 load values ss esp respectively allows kernel use different stack user program also stack unique user program new feature introduced amd64 extensions called interrupt stack table ist also resides tss contains logical segment+offset stack pointers interrupt descriptor table specifies ist entry use 8 processor load new stack ist instead allows known-good stacks used case serious errors nmi double fault example previously entry exception interrupt idt pointed task gate causing processor switch task pointed task gate original register values saved tss current time interrupt exception occurred processor set registers including ss esp known value specified tss saved selector previous tss problem hardware task switching supported amd64 16-bit selector allows linking tss previous one used hardware task switching see ia-32 manuals details although tss could created task running computer linux kernel creates one tss cpu uses tasks approach selected provides easier portability architectures example amd64 architecture support hardware task switches improved performance flexibility linux uses i/o port permission bitmap inner stack features tss features needed hardware task switches linux kernel use x86 exception vector 10 called invalid tss exception ts issued processor whenever something goes wrong tss access example interrupt happens cpl=3 transferring control cpl=0 tss used extract ss0 esp0/rsp0 stack switch task register holds bad tss selector ts fault generated invalid tss exception never happen normal operating system operation always related kernel bugs hardware failure details tss exceptions see volume 3a chapter 6 ia-32 manual x86-64 architecture support hardware task switches however tss still used machine running 64 bit extended modes modes tss still useful stores also task register expanded modes able hold 64-bit base address
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Computer architecture
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british irish legal information institute british irish legal information institute bailii pronounced bailey provides legal information especially reports cases decided courts united kingdom generally decisions england wales ireland northern ireland scotland european union european court human rights put online partial online database british irish legislation case law law reform reports treaties legal scholarship traditionally legal information accessible law report usually written private individuals groups court judgments official reports recently historically court judgment would simply spoken publication precedents built depended record interested third parties year books recorded judgments 1268 1535 probably compiled law students people like judge sir edward coke 1572 1615 created series reports would necessarily accurate record said recorded might selective inaccurate reporting industry developed people became involved specialised particular areas law incorporated council law reporting created 1885 released copies various cases still could gaps reporting however advent internet possible access multiple databases fee online particularly westlaw lexis however freely available source yet made bailii set long hard campaign various activists including senior members society computers law then-chairman neil cameron barrister laurie west-knights qc lord saville lord justice brooke concerned lack availability court judgments ordinary court users inspired australasian legal information institute austlii lii aim provide free access publicly available legal information 2006 bailii included 5 jurisdictions fourteen databases bailii website jointly hosted institute advanced legal studies university london university college cork law school bailii uses neutral citation method quickly adopted standard citation cases different series cases bailii produces follows bailii received criticisms due restrictions imposes usage guardian editorial noted bailii done wonderful job making case law freely accessible lawyers including historic european data otherwise difficult find however also noted small charity service struggles afford host 297,000 judgments allow search engines index instances even clear whether crown judge concerned holds copyright words reproducing site forbidden organization known judgmental established scrape information bailii make indexable search engines founding members judgmental included francis irving one developers theyworkforyou judgmental shut threat legal action regarding court records libel case former bailii chairman henry brooke defended criticisms stating restrictions indexing ensure records could retroactively edited removed clerical legal reasons errors information authorized published records properly anonymized brooke went explain bailii consider taking extra step making judgments searchable using google search engines necessary order achieve primary objective making judgments courts freely available public also stated restriction redistribution protect value-added content converting suitable format making efforts prevent publication material must published much material available bailii duplicated elsewhere example legislation rulings courts supreme court bailii agreement ministry justice indemnifying legal prosecutions bailii historically received payment part contract 2010/2011 tax year bailii received part contract
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Databases
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modified ami code modified ami codes digital telecommunications technique maintain system synchronization alternate mark inversion ami line codes modified deliberate insertion bipolar violations several types modified ami codes used various t-carrier e-carrier systems clock rate incoming t-carrier extracted bipolar line code signal transition provides opportunity receiver see transmitter clock ami code guarantees transitions always present mark 1 bit missing adjacent spaces 0 bits prevent loss synchronization long string zeros present payload deliberate bipolar violations inserted line code create sufficient number transitions maintain synchronization form run length limited coding receive terminal equipment recognizes bipolar violations removes user data marks attributable bipolar violations t-carrier originally developed voice applications voice signals digitized transmission via t-carrier data stream always includes ample 1 bits maintain synchronization help μ-law algorithm digitizing voice signals encodes silence continuous stream 1 bits however used transmission digital data conventional ami line code may fail sufficient marks permit recovery incoming clock synchronization lost happens many consecutive zeros user data transported exact pattern bipolar violations transmitted given case depends line rate i.e level line code t-carrier hierarchy polarity last valid mark user data prior unacceptably long string zeros would useful violation immediately following mark would produce transition reason modified ami codes include space 0 bit violation mark descriptions b denotes balancing mark opposite polarity preceding mark v denotes bipolar violation mark polarity preceding mark order preserve ami coding desirable absence dc bias number positive marks must equal number negative marks happens automatically balancing b marks line code must ensure positive negative violation marks balance first technique used ensure minimum density marks zero code suppression form bit stuffing set least significant bit 8-bit byte transmitted 1 bit already unavailable due robbed-bit signaling avoided need modify ami code way limited available data rates 56,000 bits per second per ds0 voice channel also low minimum density ones 12.5 sometimes led increased clock slippage span increased demand bandwidth compatibility g.703 isdn pri standards called 64,000 bits per second led system superseded b8zs commonly used north american t1 digital signal 1 1.544 mbit/s line code bipolar eight-zero substitution b8zs replaces string 8 consecutive zeros special pattern 000vb0vb depending polarity preceding mark could 000+−0−+ 000−+0+− north american t2 rate 6.312 mbit/s bipolar violations inserted 6 consecutive zeros occur line code called bipolar six-zero substitution b6zs replaces 6 consecutive zeros pattern 0vb0vb depending polarity preceding mark could 0+−0−+ 0−+0+− used levels european e-carrier system high density bipolar order 3 hdb3 code replaces instance 4 consecutive 0 bits one patterns 000v b00v choice made ensure consecutive violations differing polarity i.e. separated odd number normal − marks rules applied code built original string every time 4 consecutive zeros code replaced either 000− 000+ +00+ −00− determine pattern use one must count number pluses number minuses − since last violation bit v subtract one result odd number 000− 000+ used result even number +00+ −00− used determine polarity use one must look pulse preceding four zeros 000v form must used v simply copies polarity last pulse b00v form must used b v chosen opposite polarity last pulse examples bit streams codes ami hdb3 assume starting conditions previous 1 bit − previous violation even number 1 bits ago e.g preceding bits could ++− north american t3 rate 44.736 mbit/s bipolar violations inserted 3 consecutive zeros occur line code called bipolar three-zero substitution b3zs similar hdb3 run 3 consecutive zeros replaced 00v b0v choice made ensure consecutive violations differing polarity i.e separated odd number normal b marks line codes 3 states
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Internet protocols
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bisque bioimage analysis management platform bisque free open source web-based platform exchange exploration large complex datasets developed vision research lab university california santa barbara bisque specifically supports large scale multi-dimensional multimodal-images image analysis metadata stored arbitrarily nested linked tag/value pairs allowing domain-specific data organization image analysis modules added perform complex analysis tasks compute clusters analysis results stored within database querying processing data analysis provenance maintained reproducibility results bisque easily deployed cloud computing environments computer clusters scalability bisque integrated nsf cyberinfrastructure project cyverse user interacts bisque via modern web browser project bisque originally started 2004 part us national science foundation nsf supported center bio-image informatics ucsb facilitate integration database image analysis methods specifically context microscopy images given diversity imaging equipment image formats urgent need access multiple formats uniform way importantly also need maintaining analysis provenance reproducing image analysis results early realized bisque go schema-less support needs diverse biological experiments—each experiment analysis results unique slightly different beginning bisque focused using web browser standard interface posed unique database visualization challenges dealing large scale multimodal data process bisque developed unique novel framework visualizing large images 100k x 100k pixels example currently supports 250 different image file formats within browser users visualize 2d 3d 4d 5d images export many standardized formats years bisque team closely worked iplant cyberinfrastructure cyverse supporting image database management needs plant biology community going beyond bioimaging applications bisque used analyzing underwater images video ref medical imaging applications current bisque interface supports latest dicom standard bisque integrated 100 different image features feature service next release include support deep learning methods feature classification services bisque provides online resource management analysis 5d biological images addition image collection management system facilitates common biological workflows typical biological images imaging experimental annotation repeated analysis presentation images results image metadata ingestion first step using bisque ingestion either happen web browser-based interface via bisque api date bisque supports 240 different image formats generic jpeg specialized microscopy image formats zeiss czi imaris ims nikon nd2 images arbitrarily large automatically pyramided ingestion guarantees fluent user experience panning zooming image viewer addition image data bisque also captures metadata image e.g. camera settings geo coordinates etc attaches image tags images metadata organized tags name–value pairs associated image bisque allows arbitrary number tags per resource arbitrary nesting tags similar xml documents provides flexible way managing information tailored needs underlying imaging project efficiency reliability tags values stored indexed tag/value table underlying sql database graphical annotations stored addition tags include simple objects points lines circles complex objects region outlines graphical objects stored indexed underlying database well addition searchable graphical annotation also rendered bisque image viewer overlays top viewed image users typically locate images interest browsing collections searching specific queries former bisque provides web-based tag organizer enables rapid filtering grouping large image collections tag names values latter bisque offers restful tag query interface find images specific tag values search capabilities converted sql queries tag/value table behind scenes besides tag-centric image organization bisque also provides traditional folder view allows users browse images navigating folders similar file manager bisque allows users write analysis modules programming language choice e.g. matlab python c++ using language-specific apis modules typically read images metadata generate new images additional metadata output results stored back system form tags graphical objects and/or images images metadata never over-written order preserve complete provenance information tested modules registered bisque system execution bisque supports different execution modes depending available infrastructure simple modules bisque execute single node high-performance needs bisque leverage htcondor high-throughput computing software framework coarse-grained distributed parallelization latter case bisque automatically parallelize analysis large image datasets collect results single bisque metadata document metadata bisque take many forms text objects interest user annotations another web-based file e.g associated publication pdf textual graphical markup viewing editing available web 5d image viewer viewer used image object browsing ground-truth acquisition statistical summaries biological objects additionally allows various visualization options channel mapping image enhancement projections rotations recent image viewer able present volumetric imagery 3d without browser plug-ins utilizing modern browsers webgl capabilities biological image sharing often difficult due proprietary formats bisque sharing images metadata analysis results performed web system contains export facility allows conversions image formats application variety image-processing operations export textual graphical annotations xml csv google docs services modules accessible via standard web access methods http permits wide variety tools web browsers custom analysis applications interact bisque bisque services implemented using restful design pattern architecture exposes resources uris resources manipulated using common http methods among many benefits attributed restful pattern scalability web caches use client side state processing resources bisque services exchange data xml format easy integration existing software bisque also provides api covers aspects resource ingestion search analysis manipulation currently available python matlab bisque used manage analyze 23.3 hours 884gb high definition video dives bering sea submarine canyons evaluate density fishes structure-forming corals sponges document describe fishing damage non-overlapping frames extracted video transect constant frequency 1 frame per 30s image processing algorithm developed matlab used detect laser dots projected onto seafloor scale reference bisque module system allows wrap matlab code analysis module parallelized across compute cluster addition frame manually annotated objects interest e.g. fishes sponges substrates annotations image metadata e.g. pixel resolution gps location stored bisque flexible metadata store annotations used compute average density species co-habitation behavior different regions canyons resulting new insights ecosystem bisque platform part iplant cyberinfrastructure cyverse analyze plant-related images context phenotype analysis bisque integrated iplant ’ authentication cloud storage high-performance grid computing infrastructure configured sample data algorithms designed assay phenotypes directional root-tip growth comparisons seed size differences version 0.5.5 bisque released modified bsd license requires proper visible attribution bisque project whole parts bisque used either research commercial purposes
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Distributed computing architecture
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axia netmedia axia netmedia designs operates wholesale component several open access fibre based internet data networks axia operates alberta supernet half owner covage networks developing high speed networks france also awarded tender singapore fibre network part opennet consortium singapore telecom placed bond allow submit proposal australia national broadband network axia market cap 160m october 2014 axia member public-private partnership constructed alberta supernet—a provincial layer 3 network connects public facilities rural communities across alberta network wholesale sales managed axia built bell canada owned alberta government june 29 2018 service alberta announced declined renew contract axia reached multi-year deal bell assume operations supernet bell canada subsequently announced following monday agreed acquire axia alberta assets covage french joint venture axia netmedia cube infrastructure fund €1.1 million private equity fund direct involvement 40 regional networks france national backbone 9,000 km fiber deployed covage leading neutral independent player optic fiber concession business france opennet consortium consisting axia netmedia 30 singapore telecommunications/singtel 30 singapore press holdings 25 singapore power telemedia 15 awarded singapore national broadband network passive network tender september 26 2008 opennet directly fibre links proposal reach 60 population 2010 95 2012 opennet assume universal service obligations 2013 proposal creates open access network 4 distinct layers ownership separate competitive interests monopoly aspects network singtel national incumbent transfer existing ducts manholes exchanges used nbn independent asset company mid-2011 sell stake entity 2014 fibre belong opennet electronics offered operating companies opco licensees operate electronics—layers 2 3— network operating companies resell retail providers axia netmedia submitted bid build australia national broadband network nbn nbn request proposal involved design operation open access nationwide network delivering speeds 12mbit/s higher 98 australia population rfp terminated australian government april 7 2009
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Web technology
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multiplex baseband telecommunication term multiplex baseband following meanings example output group multiplexer consists band frequencies 60 khz 108 khz group-level baseband results combining 12 voice-frequency input channels bandwidth 4 khz including guard bands turn 5 groups multiplexed super group baseband 312 khz 552 khz baseband however represent group-level baseband ten super groups turn multiplexed one master group output baseband may used modulate microwave-frequency carrier
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Internet protocols
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lenovo p2 lenovo p2 android smartphone focused battery life developed lenovo officially announced september 3 2016 ifa show held berlin released november 2016 successor lenovo vibe p1 device available graphite grey champagne gold colour variants one devices 5000+ mah battery super slim full-metal unibody design terms specifications device sports 5.5-inch full hd super amoled display 1920 x 1080 resolution 401ppi powered 14 nm 2 ghz 64-bit octa-core qualcomm snapdragon 625 msm8953 processor paired 3gb 4gb ram lenovo p2 includes internal storage 32gb expanded 128gb via microsd card two nano sim card slots one slot used sim second slot used either sim sd card smartphone equipped 13mp pdaf rear camera sony sensor led flash 5mp front facing camera selfie device includes nfc usb otg fm radio a-gps bluetooth v4.1 wi-fi 802.11 a/b/g/n/ac wifi hotspot connectivity featured sensors accelerometer proximity sensor ambient light sensor compass gyroscope always active fingerprint scanner also offers gestures etc lenovo p2 launched android 6.0.1 marshmallow rom released year p2 release april 2017 p2 officially received android 7.0 nougat update 2gb size update via ota air update update brings features split-screen new notification control data saver security updates latest android security patch level november 1 2017 build number p2a42_s251_171107_row powered 5100 mah battery one highest-capacity batteries class give three days battery backup normal use physical power saver switch extends battery life reverse charging feature phone works 24w quick charger rapidly charge battery rapid charge function utilized phone turned completely comes pre-installed apps google maps hangouts play music play movies youtube gmail news weather photos drive chrome play store sar values smartphone
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Operating systems
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multiplexing telecommunications computer networks multiplexing sometimes contracted muxing method multiple analog digital signals combined one signal shared medium aim share scarce resource example telecommunications several telephone calls may carried using one wire multiplexing originated telegraphy 1870s widely applied communications telephony george owen squier credited development telephone carrier multiplexing 1910 multiplexed signal transmitted communication channel cable multiplexing divides capacity communication channel several logical channels one message signal data stream transferred reverse process known demultiplexing extracts original channels receiver end device performs multiplexing called multiplexer mux device performs reverse process called demultiplexer demux dmx inverse multiplexing imux opposite aim multiplexing namely break one data stream several streams transfer simultaneously several communication channels recreate original data stream computing i/o multiplexing also used refer concept processing multiple input/output events single event loop system calls like poll select unix multiple variable bit rate digital bit streams may transferred efficiently single fixed bandwidth channel means statistical multiplexing asynchronous mode time-domain multiplexing form time-division multiplexing digital bit streams transferred analog channel means code-division multiplexing techniques frequency-hopping spread spectrum fhss direct-sequence spread spectrum dsss wireless communications multiplexing also accomplished alternating polarization horizontal/vertical clockwise/counterclockwise adjacent channel satellite phased multi-antenna array combined multiple-input multiple-output communications mimo scheme wired communication space-division multiplexing also known space-division multiple access use separate point-to-point electrical conductors transmitted channel examples include analogue stereo audio cable one pair wires left channel another right channel multi-pair telephone cable switched star network telephone access network switched ethernet network mesh network wireless communication space-division multiplexing achieved multiple antenna elements forming phased array antenna examples multiple-input multiple-output mimo single-input multiple-output simo multiple-input single-output miso multiplexing ieee 802.11g wireless router k antennas makes principle possible communicate k multiplexed channels peak bit rate 54 mbit/s thus increasing total peak bit rate factor k different antennas would give different multi-path propagation echo signatures making possible digital signal processing techniques separate different signals techniques may also utilized space diversity improved robustness fading beamforming improved selectivity rather multiplexing frequency-division multiplexing fdm inherently analog technology fdm achieves combining several signals one medium sending signals several distinct frequency ranges single medium fdm signals electrical signals one common applications fdm traditional radio television broadcasting terrestrial mobile satellite stations cable television one cable reaches customer residential area service provider send multiple television channels signals simultaneously cable subscribers without interference receivers must tune appropriate frequency channel access desired signal variant technology called wavelength-division multiplexing wdm used optical communications time-division multiplexing tdm digital rare cases analog technology uses time instead space frequency separate different data streams tdm involves sequencing groups bits bytes individual input stream one way associated appropriate receiver done sufficiently quickly receiving devices detect circuit time used serve another logical communication path consider application requiring four terminals airport reach central computer terminal communicated 2400 baud rather acquire four individual circuits carry low-speed transmission airline installed pair multiplexers pair 9600 baud modems one dedicated analog communications circuit airport ticket desk back airline data center also installed web proxy servers e.g polipo use tdm http pipelining multiple http transactions onto tcp/ip connection carrier sense multiple access multidrop communication methods similar time-division multiplexing multiple data streams separated time medium signals separate origins instead combined single signal best viewed channel access methods rather form multiplexing td legacy multiplexing technology still providing backbone national fixed line telephony networks europe providing 2m/bit voice signalling ports narrow band telephone exchanges dms100 e1 2m/bit tdm port provides either 30 31 speech timeslots case ccitt7 signalling systems 30 voice channels customer connected q931 dass2 dpnss v5 cass signalling systems polarization-division multiplexing uses polarization electromagnetic radiation separate orthogonal channels practical use radio optical communications particularly 100 gbit/s per channel fiber optic transmission systems orbital angular momentum multiplexing relatively new experimental technique multiplexing multiple channels signals carried using electromagnetic radiation single path potentially used addition physical multiplexing methods greatly expand transmission capacity systems still early research phase small-scale laboratory demonstrations bandwidths 2.5 tbit/s single light path controversial subject academic community many claiming new method multiplexing rather special case space-division multiplexing code division multiplexing cdm code division multiple access cdma spread spectrum class techniques several channels simultaneously share frequency spectrum spectral bandwidth much higher bit rate symbol rate one form frequency hopping another direct sequence spread spectrum latter case channel transmits bits coded channel-specific sequence pulses called chips number chips per bit chips per symbol spreading factor coded transmission typically accomplished transmitting unique time-dependent series short pulses placed within chip times within larger bit time channels different code transmitted fiber radio channel medium asynchronously demultiplexed advantages conventional techniques variable bandwidth possible statistical multiplexing wide bandwidth allows poor signal-to-noise ratio according shannon-hartley theorem multi-path propagation wireless communication combated rake receivers significant application cdma global positioning system gps multiplexing technique may extended multiple access method channel access method example tdm time-division multiple access tdma statistical multiplexing carrier-sense multiple access csma multiple access method makes possible several transmitters connected physical medium share capacity multiplexing provided physical layer osi model multiple access also involves media access control protocol part data link layer transport layer osi model well tcp/ip model provides statistical multiplexing several application layer data flows to/from computer code-division multiplexing cdm technique channel transmits bits coded channel-specific sequence pulses coded transmission typically accomplished transmitting unique time-dependent series short pulses placed within chip times within larger bit time channels different code transmitted fiber asynchronously demultiplexed widely used multiple access techniques time-division multiple access tdma frequency-division multiple access fdma code-division multiplex techniques used access technology namely code-division multiple access cdma universal mobile telecommunications system umts standard third-generation 3g mobile communication identified itu earliest communication technology using electrical wires therefore sharing interest economies afforded multiplexing electric telegraph early experiments allowed two separate messages travel opposite directions simultaneously first using electric battery ends one end telephony customer telephone line typically ends remote concentrator box multiplexed along telephone lines neighborhood similar area multiplexed signal carried central switching office significantly fewer wires much distances customer line practically go likewise also true digital subscriber lines dsl fiber loop fitl common method multiplexing uses optical fiber backbone connects pots phone lines rest pstn also replaces dsl connecting directly ethernet wired home asynchronous transfer mode often communications protocol used cable tv long carried multiplexed television channels late 20th century began offering services telephone companies iptv also depends multiplexing video editing processing systems multiplexing refers process interleaving audio video one coherent data stream digital video transport stream normally feature container format may include metadata information subtitles audio video streams may variable bit rate software produces transport stream and/or container commonly called statistical multiplexer muxer demuxer software extracts otherwise makes available separate processing components stream container digital television systems several variable bit-rate data streams multiplexed together fixed bitrate transport stream means statistical multiplexing makes possible transfer several video audio channels simultaneously frequency channel together various services may involve several standard definition television sdtv programmes particularly dvb-t dvb-s2 isdb atsc-c one hdtv possibly single sdtv companion channel one 6 8 mhz-wide tv channel device accomplishes called statistical multiplexer several systems multiplexing results mpeg transport stream newer dvb standards dvb-s2 dvb-t2 capacity carry several hdtv channels one multiplex digital radio multiplex also known ensemble number radio stations grouped together multiplex stream digital information includes audio data communications satellites carry broadcast television networks radio networks known multiple channel per carrier mcpc multiplexing practical different sources using single transponder single channel per carrier mode used fm broadcasting analog radio media multiplexing term commonly given process adding subcarriers audio signal enters transmitter modulation occurs fact stereo multiplex signal generated using time-division multiplexing switching two left channel right channel input signals ultrasonic rate subcarrier filtering higher harmonics multiplexing sense sometimes known mpx turn also old term stereophonic fm seen stereo systems since 1960s spectroscopy term used indicate experiment performed mixture frequencies respective response unravelled afterwards using fourier transform principle computer programming may refer using single in-memory resource file handle handle multiple external resources on-disk files electrical multiplexing techniques require physical multiplexer device refer keyboard matrix charlieplexing design style high-throughput dna sequencing term used indicate artificial sequences often called barcodes indexes added link given sequence reads given sample thus allow sequencing multiple samples reaction
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Internet protocols
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unix system v unix system v pronounced system five one first commercial versions unix operating system originally developed first released 1983 four major versions system v released numbered 1 2 3 4 system v release 4 svr4 commercially successful version result effort marketed unix system unification solicited collaboration major unix vendors source several common commercial unix features system v sometimes abbreviated sysv unix market divided five system v variants ibm aix hewlett-packard hp-ux oracle solaris xinuos unixware illumos distributions open-source opensolaris continuation system v successor 1982 unix system iii developed sold hardware ran system v customers ran version reseller based reference implementation standards document called system v interface definition outlined default features behavior implementations formative years computer business division went several phases system v software groups beginning unix support group usg followed unix system development laboratory usdl followed information systems attis finally unix system laboratories usl 1980s early-1990s unix system v berkeley software distribution bsd two major version unix historically bsd also commonly called bsd unix berkeley unix eric s. raymond summarizes longstanding relationship rivalry system v bsd early period hp ibm others chose system v basis unix offerings vendors sun microsystems dec extended bsd throughout development though system v infused features bsd bsd variants dec ultrix received system v features sun microsystems worked together merge system v bsd-based sunos produce solaris one primary system v descendants still use today since early 1990s due standardization efforts posix commercial success linux division system v bsd become less important system v known inside bell labs unix 5.0 succeeded previous commercial unix called system iii january 1983 unix 4.0 never released externally would designated system iv first release system v called system v.0 system v release 1 svr1 developed unix support group usg based bell labs internal usg unix 5.0 system v also included features vi editor curses 4.1 bsd developed university california berkeley also improved performance adding buffer inode caches also added support inter-process communication using messages semaphores shared memory developed earlier bell-internal cb unix svr1 ran dec pdp-11 vax minicomputers unix support group usg transformed unix system development laboratory usdl released system v release 2 1984 svr2 added shell functions svid svr2.4 added demand paging copy-on-write shared memory record file locking concept porting base formalized dec vax-11/780 chosen release porting base so-called original version release porting efforts machines emanate educational source licenses svr2 offered us 800 first cpu 400 additional cpu commercial source license offered 43,000 three months support 16,000 price per additional cpu apple computer a/ux operating system initially based release sco xenix also used svr2 basis first release hp-ux also svr2 derivative maurice j. bach book design unix operating system definitive description svr2 kernel unix system development laboratory usdl succeeded information systems attis distributed unix system v release 3 1987 svr3 included streams remote file sharing rfs file system switch fss virtual file system mechanism restricted form shared libraries transport layer interface tli network api final version release 3.2 1988 added binary compatibility xenix intel platforms see intel binary compatibility standard user interface improvements included layers windowing system dmd 5620 graphics terminal svr3.2 curses libraries offered eight color pairs time important features forms panels menus etc. 3b2 became official porting base sco unix based upon svr3.2 isc 386/ix among obscure distributions svr3.2 386 esix 3.2 everex system v release 3.2 sold intel two shipped plain vanilla codebase ibm aix operating system svr3 derivative system v release 4.0 announced october 18 1988 incorporated variety commercial unix products early 1989 onwards joint project unix system laboratories sun microsystems combined technology new features included many companies licensed svr4 bundled computer systems workstations network servers svr4 systems vendors included atari atari system v commodore amiga unix data general dg/ux fujitsu uxp/ds hitachi hi-ux hewlett-packard hp-ux ncr unix/ns nec ews-ux up-ux ux/4800 super-ux oki oki system v pyramid technology dc/osx sgi irix siemens sinix sony news-os sumitomo electric industries seiux sun microsystems solaris illumos 2010s open-source platform software porting houses also sold enhanced supported intel x86 versions svr4 software vendors included dell dell unix everex esix micro station technology svr4 microport svr4 uhc svr4 primary platforms svr4 intel x86 sparc sparc version called solaris 2 internally sunos 5.x developed sun relationship sun terminated release svr4 meaning later versions solaris inherit features later svr4.x releases sun would 2005 release source code solaris 10 sunos 5.10 open-source opensolaris project creating forks open-source albeit heavily modified system v implementation available oracle took sun solaris forked proprietary release illumos continuation project developed open-source consortium intel-based resellers including unisys icl ncr corporation olivetti developed svr4.0mp multiprocessing capability allowing system calls processed processor interrupt servicing master processor release 4.1 es enhanced security added security features required orange book b2 compliance access control lists support dynamic loading kernel modules 1992 usl engaged joint venture novell called univel year saw release system v.4.2 univel unixware featuring veritas file system vendors included uhc consensys release 4.2mp completed late 1993 added support multiprocessing released unixware 2 1995 eric s. raymond warned prospective buyers svr4.2 versions often include on-line man pages 1994 buyers guide attributes change policy unix system laboratories santa cruz operation sco owners xenix eventually acquired unixware trademark distribution rights system v release 4.2 codebase novell vendors sun ibm hp continued use extend system v release 4 novell transferred ownership unix trademark open group operating system meets single unix specification sus effectively successor system v interface definition may granted unix rights sus met apple macos bsd derivative well several operating systems derived either bsd system v. system v release 5 developed 1997 santa cruz operation sco merger sco openserver svr3-derivative unixware focus large-scale servers released sco unixware 7 sco successor sco group also based sco openserver 6 svr5 codebase used major developer reseller system v release 6 announced sco released end 2004 apparently cancelled supposed support 64-bit systems industry coalesced around open group single unix specification version 3 unix 03 see also smallfoot 1980s 1990s variety svr4 versions unix available commercially x86 pc platform however market commercial unix pcs declined linux bsd became widely available late 1994 eric s. raymond discontinued pc-clone unix software buyer guide usenet stating reason dropping run linux longer find svr4 market interesting significant 1998 confidential memo microsoft stated linux track eventually x86 unix market predicted believe linux – moreso nt – biggest threat sco near future infoworld article 2001 characterized sco unixware bleak outlook due trounced market linux solaris idc predicted sco would continue see shrinking share market project monterey started 1998 combine major features existing commercial unix platforms joint project compaq ibm intel sco sequent computer systems target platform meant intel new ia-64 architecture itanium line processors however project abruptly canceled 2001 little progress 2001 several major unix variants sco unixware compaq tru64 unix sgi irix decline three major unix versions well market ibm aix hewlett-packard hp-ux sun solaris 2006 sgi declared bankruptcy analysts questioned whether linux would replace proprietary unix altogether 2006 article written computerworld mark hall economics linux cited major factor driving migration unix linux article also cites trends high-performance computing applications evidence dramatic shift unix linux november 2015 survey top 500 supercomputers unix used 1.2 running ibm aix linux used 98.8 survey november 2017 reports 100 using linux system v derivatives continued deployed proprietary server platforms principal variants system v remain commercial use aix ibm solaris oracle hp-ux hp according study done idc 2012 worldwide unix market divided ibm 56 oracle 19.2 hp 18.6 commercial unix vendor 2 market industry analysts generally characterize proprietary unix entered period slow permanent decline opensolaris derivatives svr4 descendants open-source software core system software continues developed illumos used illumos distributions smartos openindiana others system v interprocess communication mechanisms available unix-like operating systems derived system v particular linux reimplementation unix well bsd derivative freebsd posix 2008 specifies replacement interfaces freebsd maintains binary compatibility layer coff format allows freebsd execute binaries compiled svr3.2 derivatives sco unix interactive unix modern system v linux bsd platforms use elf file format natively compiled binaries
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Operating systems
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dynamic host configuration protocol dynamic host configuration protocol dhcp network management protocol used udp/ip networks whereby dhcp server dynamically assigns ip address network configuration parameters device network communicate ip networks dhcp server enables computers request ip addresses networking parameters automatically internet service provider isp reducing need network administrator user manually assign ip addresses network devices absence dhcp server computer device network needs manually assigned ip address assign apipa address enable communicate outside local subnet dhcp implemented networks ranging size home networks large campus networks regional internet service provider networks router residential gateway enabled act dhcp server residential network routers receive globally unique ip address within isp network within local network dhcp server assigns local ip address device connected network 1984 reverse address resolution protocol rarp defined rfc 903 introduced allow simple devices diskless workstations dynamically obtain suitable ip address however acted data link layer made implementation difficult many server platforms also required server present individual network link rarp superseded bootstrap protocol bootp defined rfc 951 september 1985 introduced concept relay agent allowed forwarding bootp packets across networks allowing one central bootp server serve hosts many ip subnets dhcp based bootp dynamically allocate ip addresses pool reclaim longer use also used deliver wide range extra configuration parameters ip clients including platform-specific parameters dhcp first defined rfc 1531 october 1993 due errors editorial process almost immediately reissued rfc 1541 four years later dhcpinform message type small changes added rfc 2131 remains standard ipv4 networks dhcpv6 initially described rfc 3315 2003 updated many subsequent rfcs rfc 3633 added dhcpv6 mechanism prefix delegation stateless address autoconfiguration added rfc 3736 udp/ip defines devices one network communicate devices another network dhcp server manage udp/ip settings devices network automatically dynamically assigning ip addresses devices dhcp operates based client–server model computer device connects network dhcp client software sends dhcp broadcast query requesting necessary information dhcp server network may service request dhcp server manages pool ip addresses information client configuration parameters default gateway domain name name servers time servers receiving dhcp request dhcp server may respond specific information client previously configured administrator specific address information valid entire network time period allocation lease valid dhcp client typically queries information immediately booting periodically thereafter expiration information dhcp client refreshes assignment initially requests parameter values dhcp server may assign new address based assignment policies set administrators large networks consist multiple links single dhcp server may service entire network aided dhcp relay agents located interconnecting routers agents relay messages dhcp clients dhcp servers located different subnets depending implementation dhcp server may three methods allocating ip addresses dhcp used internet protocol version 4 ipv4 ipv6 versions serve purpose details protocol ipv4 ipv6 differ sufficiently may considered separate protocols ipv6 operation devices may alternatively use stateless address autoconfiguration ipv6 hosts may also use link-local addressing achieve operations restricted local network link dhcp employs connectionless service model using user datagram protocol udp implemented two udp port numbers operations bootstrap protocol bootp udp port number 67 destination port server udp port number 68 used client dhcp operations fall four phases server discovery ip lease offer ip lease request ip lease acknowledgement stages often abbreviated dora discovery offer request acknowledgement dhcp operation begins clients broadcasting request client server different subnets dhcp helper dhcp relay agent may used clients requesting renewal existing lease may communicate directly via udp unicast since client already established ip address point additionally broadcast flag 1 bit 2 byte flags field bits reserved set 0 client use indicate way broadcast unicast receive dhcpoffer 0x8000 broadcast 0x0000 unicast usually dhcpoffer sent unicast hosts accept unicast packets ip addresses configured flag used work around issue dhcp client broadcasts dhcpdiscover message network subnet using destination address 255.255.255.255 limited broadcast specific subnet broadcast address directed broadcast dhcp client may also request last known ip address client remains connected network server may grant request otherwise depends whether server set authoritative authoritative server denies request causing client issue new request non-authoritative server simply ignores request leading implementation-dependent timeout client expire request ask new ip address example htype set 1 specify medium used ethernet hlen set 6 ethernet address mac address 6 octets long chaddr set mac address used client options set well dhcp server receives dhcpdiscover message client ip address lease request dhcp server reserves ip address client makes lease offer sending dhcpoffer message client message contains client client id traditionally mac address ip address server offering subnet mask lease duration ip address dhcp server making offer dhcp server may also take notice hardware-level mac address underlying transport layer according current rfcs transport layer mac address may used client id provided dhcp packet dhcp server determines configuration based client hardware address specified chaddr client hardware address field server 192.168.1.1 specifies client ip address yiaddr ip address field response dhcp offer client replies dhcprequest message broadcast server requesting offered address client receive dhcp offers multiple servers accept one dhcp offer based required server identification option request broadcast messaging servers informed whose offer client accepted dhcp servers receive message withdraw offers made client return offered ip address pool available addresses dhcp server receives dhcprequest message client configuration process enters final phase acknowledgement phase involves sending dhcpack packet client packet includes lease duration configuration information client might requested point ip configuration process completed protocol expects dhcp client configure network interface negotiated parameters client obtains ip address probe newly received address e.g arp address resolution protocol prevent address conflicts caused overlapping address pools dhcp servers dhcp client may request information server sent original dhcpoffer client may also request repeat data particular application example browsers use dhcp inform obtain web proxy settings via client sends request dhcp server release dhcp information client deactivates ip address client devices usually know users may unplug network protocol mandate sending dhcp release dhcp server provide optional configuration parameters client rfc 2132 describes available dhcp options defined internet assigned numbers authority iana dhcp bootp parameters dhcp client select manipulate overwrite parameters provided dhcp server unix-like systems client-level refinement typically takes place according values configuration file /etc/dhclient.conf options octet strings varying length first octet option code second octet number following octets remaining octets code dependent example dhcp message-type option offer would appear 0x35 0x01 0x02 0x35 code 53 dhcp message type 0x01 means one octet follows 0x02 value offer following tables list available dhcp options listed rfc 2132 iana registry option exists identify vendor functionality dhcp client information variable-length string characters octets meaning specified vendor dhcp client one method dhcp client utilize communicate server using certain type hardware firmware set value dhcp requests called vendor class identifier vci option 60 method allows dhcp server differentiate two kinds client machines process requests two types modems appropriately types set-top boxes also set vci option 60 inform dhcp server hardware type functionality device value option set gives dhcp server hint required extra information client needs dhcp response relay agent information option option 82 specifies container attaching sub-options dhcp requests transmitted dhcp relay dhcp server small networks one ip subnet managed dhcp clients communicate directly dhcp servers however dhcp servers also provide ip addresses multiple subnets case dhcp client yet acquired ip address communicate directly dhcp server using ip routing routable ip address know link layer address router know ip address dhcp server order allow dhcp clients subnets directly served dhcp servers communicate dhcp servers dhcp relay agents installed subnets dhcp client broadcasts local link relay agent receives broadcast transmits one dhcp servers using unicast relay agent stores ip address field giaddr field dhcp packet dhcp server uses giaddr-value determine subnet relay agent received broadcast allocates ip address subnet dhcp server replies client sends reply giaddr-address using unicast relay agent retransmits response local network situation communication relay agent dhcp server typically uses source destination udp port 67 dhcp ensures reliability several ways periodic renewal rebinding failover dhcp clients allocated leases last period time clients begin attempt renew leases half lease interval expired sending unicast dhcprequest message dhcp server granted original lease server unreachable fail respond dhcprequest however case client repeats dhcprequest time time dhcp server comes back becomes reachable dhcp client succeed contacting renew lease dhcp server unreachable extended period time dhcp client attempt rebind broadcasting dhcprequest rather unicasting broadcast dhcprequest message reach available dhcp servers dhcp server able renew lease time order rebinding work client successfully contacts backup dhcp server server must accurate information client binding maintaining accurate binding information two servers complicated problem servers able update lease database must mechanism avoid conflicts updates independent servers proposal implementing fault-tolerant dhcp servers submitted internet engineering task force never formalized rebinding fails lease eventually expire lease expires client must stop using ip address granted lease time restart dhcp process beginning broadcasting codice_1 message since lease expired accept ip address offered new ip address presumably different dhcp server able use network however since ip address changed ongoing connections broken 2018 dhcp remains widely-used automatically assign ip addresses newer iterations assigning ip addresses include dhcpv6 slaac base dhcp include mechanism authentication vulnerable variety attacks attacks fall three main categories client way validate identity dhcp server unauthorized dhcp servers commonly called rogue dhcp operated networks providing incorrect information dhcp clients serve either denial-of-service attack preventing client gaining access network connectivity man-in-the-middle attack dhcp server provides dhcp client server ip addresses ip address one dns servers attacker convince dhcp client dns lookups dns server therefore provide answers dns queries client turn allows attacker redirect network traffic allowing eavesdrop connections client network servers contacts simply replace network servers dhcp server secure mechanism authenticating client clients gain unauthorized access ip addresses presenting credentials client identifiers belong dhcp clients also allows dhcp clients exhaust dhcp server store ip addresses—by presenting new credentials time asks address client consume available ip addresses particular network link preventing dhcp clients getting service dhcp provide mechanisms mitigating problems relay agent information option protocol extension rfc 3046 usually referred industry actual number option 82 allows network operators attach tags dhcp messages messages arrive network operator trusted network tag used authorization token control client access network resources client access network upstream relay agent lack authentication prevent dhcp server operator relying authorization token another extension authentication dhcp messages rfc 3118 provides mechanism authenticating dhcp messages 2002 nowiki rfc 3118 /nowiki seen widespread adoption problems managing keys large numbers dhcp clients 2007 book dsl technologies remarked numerous security vulnerabilities identified security measures proposed rfc 3118 fact combined introduction 802.1x slowed deployment take-rate authenticated dhcp never widely deployed 2010 book notes implementations dhcp authentication challenges key management processing delays due hash computation deemed heavy price pay perceived benefits architectural proposals 2008 involve authenticating dhcp requests using 802.1x pana transport eap ietf proposal made including eap dhcp so-called eapodhcp appear progressed beyond ietf draft level last dates 2010
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Internet protocols
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aliens computer game 1986 video game aliens computer game video game developed published activision commodore 64 apple ii zx spectrum computer systems based film title also known aliens us europe initially planned released aliens second part aliens series six minigames strung together via graphical interactive sequences akin adventure game though interaction possible advancing dialog displayed speech balloons minigames mostly action sequences involve piloting ship sulaco planet surface recognizing equipment fighting aliens time release game received mixed reviews including scores 85 commodore format 8/10 averaged computer video games 4/10 crash 5/10 sinclair user 9/10 sinclair 60 zzap 64 info gave commodore 64 version four stars five aliens appropriately creepy sequence well done plays quite differently others venturebeat stephen kleckner commented 2014 feature lot compilation-designed titles aliens falls trap collection mediocre experiences instead game singular focus … hardcore fans commodore 64 load one everyone else ’ missing much let play video wo n't provide hand chris cummins topless robot wrote 2010 now-crude graphics aside still arguably best game based films alien saga
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Computer architecture
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ethernet first mile ethernet first mile efm refers using one ethernet family computer network protocols telecommunications company customer premises customer point view first mile although access network point view known last mile working group institute electrical electronics engineers ieee produced standards known ieee 802.3ah-2004 later included overall standard ieee 802.3-2008 although often used businesses also known ethernet home etth one family standards known ethernet passive optical network epon uses passive optical network wide metro local area networks using various forms ethernet goal eliminate non-native transport ethernet asynchronous transfer mode atm access networks one early effort etherloop technology invented nortel networks 1996 spun company elastic networks 1998 principal inventor jack terry hope combine packet-based nature ethernet ability digital subscriber line dsl technology work existing telephone access wires name comes local loop traditionally describes wires telephone company office subscriber protocol half-duplex control provider side loop adapted line conditions peak 10 mbit/s advertised 4-6 mbit/s typical distance symbol rates 1 megabaud 1.67 megabaud 2 4 6 bits per symbol etherloop product name registered trademark us canada etherloop technology eventually purchased paradyne networks 2002 turn purchased zhone technologies 2005 another effort concept promoted michael silverton using ethernet variants used fiber optic communication residential well business customers example become known fiber home ftth fiberhood networks company provided service 1999 2001 early products around year 2000 marketed 10bases infineon technologies although technically use baseband signalling rather passband very-high-bit-rate digital subscriber line vdsl technology patent filed 1997 peleg shimon porat boaz noam alroy rubinstain avinoam sfadya yackow long reach ethernet product name used cisco systems starting 2001 supported modes 5 mbit/s 10 mbit/s 15 mbit/s depending distance october 2000 howard frazier issued call interest ethernet last mile november 2000 meeting ieee 802.3 created ethernet first mile study group july 16 2001 802.3ah working group parallel participating vendors formed ethernet first mile alliance efma december 2001 promote ethernet subscriber access technology support ieee standard efforts early meeting etherloop technology called 100base-cu another technology called eovdsl ethernet vdsl working group efm standard approved june 24 2004 published september 7 2004 ieee 802.3ah-2004 2005 included base ieee 802.3 standard 2005 efma absorbed metro ethernet forum early 2006 work began even higher-speed 10 gigabit/second ethernet passive optical network 10g-epon standard ratified 2009 ieee 802.3av work epon continued ieee p802.3bk extended epon task force formed march 2012 major goals task force included adding support px30 px40 prx40 pr40 power budget classes 1g-epon 10g-epon 802.3bk amendment approved ieee-sa sb august 2013 published soon thereafter standard ieee std 802.3bk-2013 november 2011 ieee 802.3 began work epon protocol coax epoc efm defines ethernet transmitted new media types using new ethernet physical layer phy interfaces efm also addresses issues required mass deployment ethernet services operations administration management oa compatibility existing technologies plain old telephone service spectral compatibility copper twisted pair fiber home use passive optical network additionally clause 57 defines link-level oa including discovery link monitoring remote fault indication loopbacks variable access 2base-tl ieee 802.3-2008 physical layer phy specification full-duplex long-reach point-to-point ethernet link voice-grade copper wiring unlike 10base-t 100base-t 1000base-t phys providing single rate 10 100 1000 mbit/s respectively 2base-tl link rate vary depending copper media characteristics length wire diameter gauge number pairs link aggregated amount crosstalk pairs etc desired link parameters desired snr margin power back-off etc regional spectral limitations 2base-tl phys deliver minimum 2 mbit/s distances using itu-t g.991.2 g.shdsl.bis technology single copper pair phys may also support optional aggregation bonding multiple copper pairs called pme aggregation function paf single pair minimum possible link bitrate 192 kbit/s 3 x 64 kbit/s maximum bitrate 5.7 mbit/s 89 x 64 kbit/s 0.5 mm wire 3 db noise margin spectral limitations max bitrate achieved distances max achievable bitrate 850 kbit/s throughput 2base-tl link lower link bitrate average 5 due 64/65-octet encoding paf overhead factors depend packet size 10pass-ts ieee 802.3-2008 physical layer phy specification full-duplex short reach point-to-point ethernet link voice-grade copper wiring 10pass-ts phys deliver minimum 10 mbit/s distances using itu-t g.993.1 vdsl technology single copper pair phys may also support optional aggregation bonding multiple copper pairs called pme aggregation function paf unlike ethernet physical layers provide single rate 10 100 1000 mbit/s 10pass-ts link rate vary similar 2base-tl depending copper channel characteristics length wire diameter gauge wiring quality number pairs link aggregated factors vdsl short range technology designed provide broadband distances less 1 km voice-grade copper twisted pair line connection data rates deteriorate quickly line distance increases led vdsl referred fiber curb technology requires fiber backhaul connect carrier network greater distances vdsl ethernet first mile services using may useful way standardise functionality metro ethernet networks potentially distribute internet access services voice-grade wiring multi-dwelling unit buildings however vdsl2 already proven versatile faster standard greater reach vdsl
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Internet protocols
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semantic compression natural language processing semantic compression process compacting lexicon used build textual document set documents reducing language heterogeneity maintaining text semantics result ideas represented using smaller set words applications semantic compression lossy compression increased prolixity compensate lexical compression original document reconstructed reverse process semantic compression basically achieved two steps using frequency dictionaries semantic network step 1 requires assembling word frequencies information semantic relationships specifically hyponymy moving upwards word hierarchy cumulative concept frequency calculating adding sum hyponyms frequencies frequency hypernym formula_1 formula_2 hypernym formula_3 desired number words top cumulated frequencies chosen build targed lexicon second step compression mapping rules defined remaining words order handle every occurrence less frequent hyponym hypernym output text fragment text processed semantic compression words bold replaced hypernyms nest building social insects paper wasps honey bees organize colonies different ways new study researchers report despite differences insects rely network genes guide social behavior.the study appears proceedings royal society b biological sciences honey bees paper wasps separated 100 million years evolution striking differences divvy work maintaining colony procedure outputs following text facility building insect insects honey insects arrange biological groups different structure new study researchers report despite difference opinions insects act network genes steer party demeanor study appears proceeding institution bacteria biological sciences honey insects insect separated hundred million years organic processes impinging differences opinions divvy work affirming biological group natural tendency keep natural language expressions concise perceived form implicit semantic compression omitting unmeaningful words redundant meaningful words especially avoid pleonasms vector space model compacting lexicon leads reduction dimensionality results less computational complexity positive influence efficiency semantic compression advantageous information retrieval tasks improving effectiveness terms precision recall due precise descriptors reduced effect language diversity – limited language redundancy step towards controlled dictionary example possible display output natural text re-applying inflexion adding stop words
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Computational linguistics
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wsmo wsmo web service modeling ontology conceptual model relevant aspects related semantic web services provides ontology based framework supports deployment interoperability semantic web services wsmo four main components wsmo working group part essi cluster aligns research development efforts areas semantic web services several european fp6 research projects wsmo working group includes wsml working group aims developing language called web services modeling language wsml formalizes web services modeling ontology wsmo
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Web technology
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bitemporal modeling bitemporal modeling specific case temporal database information modeling technique designed handle historical data along two different timelines makes possible rewind information actually combination recorded point time order able information discarded even erroneous within example financial reporting often desirable able recreate old report actually looked time creation looked given corrections made data creation implementations bitemporal modeling mostly done using relational databases bitemporal modeling considered different dimensional modeling complementary database normalization standard provides language constructs working bitemporal data however many current solutions still vendor-specific bitemporal modeling uses bitemporal structures basic components results databases consistent type temporality data focusing completeness accuracy data bitemporal modeling facilitates creation complete audit trails data data becomes immutable specifically allows queries provide
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Databases
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acornsoft lisp acornsoft lisp marketed simply lisp dialect commercial implementation lisp programming language released early 1980s 8-bit acorn atom bbc micro acorn electron computers acornsoft lisp released cassette disk rom cartridge rom cartridge version instantaneous loading well greater amount available free ram user definitions contrast large-scale lisp implementations acornsoft variant modest number built-in definitions fit limited memory space 8-bit acorn computers interpreter implemented 6502 machine-code 5.5k size based owl lisp written mike gardner owl computers published apple ii 1979 acornsoft licensed owl computers 1981 developed acorn atom bbc microcomputer supplied lisp workspace image containing commonly used built-in functions constants 3k size although could deleted needed user free memory supported datatypes included nested lists 16-bit signed integers strings 127 characters length loop keywords available program control acornsoft also commissioned book lisp bbc microcomputer arthur norman gillian cattell published 1983 arthur norman lecturer computer science cambridge university gillian cattell research lisp cambridge book sold separately software contained examples illustrating use acornsoft specific features vdu function allowing machine-specific graphics capabilities book also contained working examples including tree-sorting program arbitrary arithmetic package animal guessing game route finding program graphics package simple compiler adventure game route-finding demo program supplied standard interpreter program loaded command codice_1 tested typing codice_2 example display output codice_3 thus showing total mileage shortest possible route listing intermediate towns visited
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Programming language topics
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gender institutions development database oecd gender institutions development gid database gid-db contains 60 data indicators gender equality gid-db introduced 2006 oecd development centre provide data tool help researchers policy makers determine analyze obstacles women social economic development provides gender-related data 162 countries afghanistan zimbabwe thereby covering regions country-income-categories world gid database structured around key traditional measurements gender equality including education data literacy rates school enrollments gender health percentage births attended skilled personnel economic status political status percentage legislators gender gid-db also introduced non-traditional data indicators social institutions cultural practices social norms affect gender equality new measurements thoroughly presented next section providing new indicator information formerly hidden instances gender discrimination database complements data compilations undp human development report world bank group genderstats database world economic forum global gender gap report gid database groups 12 social-institution indicators 5 different categories 12 indicators cultural traditional practice impacts upon gender equality indicator coded 0 indicating discrimination i.e. equality 1 indicating high discrimination high inequality depending extent discrimination percentage females suffer application specific social institution example consider inheritance second social institution indicator 10 percent female population country report restricted access inheritance daughters inheriting half amount granted sons indicator inheritance would 10 percent x 0.50 0.05 nearly equality values 0 complicated describe briefly case omitted family code civil liberties physical integrity son preference ownership rights gid database source brief descriptions namely gid-db includes complete description data indicator called metadata stays hidden one clicks indicator little red – working definitions data indicators easily available online right data gid-db statistically applied toward identifying factors determine women labour-force participation varies across database countries reported results suggest social-institution factors indicators outweigh traditional indicators income per capita gid database including social-institution indicators thus may useful solving various economic development problems offering complete set indicators choose answering policy questions research topics undp un development programme publishes two composite indexes gender equality based traditional indicators above-mentioned ones gid-db namely gender empowerment measure gem gender-related development index gdi 2009 similarly oecd development centre introduced social institutions gender index sigi described article sigi exclusively based 12 new social institutions 5 groups providing sigi 5 components given exclusive focus social institutions sigi highly specialized measure gender equality – confused gem gdi sigi 5 components added 2009 gid-db readily accessible described specific part latter data accessed via oecd website statextracts gid-db whose sidebar gid database components selected ready click 12 social institution indicators already display main part screen information working definitions data plus country notes displayed hidden clicking little red many oecd datasets listed sidebar addition gid-db data subject article
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Databases
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database normalization database normalization process structuring relational database accordance series so-called normal forms order reduce data redundancy improve data integrity first proposed edgar f. codd part relational model normalization entails organizing columns attributes tables relations database ensure dependencies properly enforced database integrity constraints accomplished applying formal rules either process synthesis creating new database design decomposition improving existing database design basic objective first normal form defined codd 1970 permit data queried manipulated using universal data sub-language grounded first-order logic sql example data sub-language albeit one codd regarded seriously flawed objectives normalization beyond 1nf first normal form stated follows codd attempt made modify update insert delete relation following undesirable side-effects may arise relations sufficiently normalized fully normalized database allows structure extended accommodate new types data without changing existing structure much result applications interacting database minimally affected normalized relations relationship one normalized relation another mirror real-world concepts interrelationships querying manipulating data within data structure normalized following non-1nf representation customers credit card transactions involves complexity really necessary br customer corresponds 'repeating group transactions automated evaluation query relating customers transactions therefore would broadly involve two stages example order find monetary sum transactions occurred october 2003 customers system would know must first unpack transactions group customer sum amounts transactions thus obtained date transaction falls october 2003 one codd important insights structural complexity reduced reduced structural complexity gives users application dbms power flexibility formulate evaluate queries normalized equivalent structure might look like modified structure key cust id first relation cust id tr id second relation row represents individual credit card transaction dbms obtain answer interest simply finding rows date falling october summing amounts data structure places values equal footing exposing dbms directly potentially participate directly queries whereas previous situation values embedded lower-level structures handled specially accordingly normalized design lends general-purpose query processing whereas unnormalized design normalized version also allows user change customer name one place guards errors arise customer name misspelled records codd introduced concept normalization known first normal form 1nf 1970 codd went define second normal form 2nf third normal form 3nf 1971 codd raymond f. boyce defined boyce-codd normal form bcnf 1974 informally relational database relation often described normalized meets third normal form 3nf relations free insertion update deletion anomalies normal forms least normalized normalized normalization database design technique used design relational database table higher normal form process progressive higher level database normalization achieved unless previous levels satisfied means data unnormalized form least normalized aiming achieve highest level normalization first step would ensure compliance first normal form second step would ensure second normal form satisfied forth order mentioned data conform sixth normal form however worth noting normal forms beyond 4nf mainly academic interest problems exist solve rarely appear practice please note data following example intentionally designed contradict normal forms real life quite possible able skip normalization steps table n't contain anything contradicting given normal form also commonly occurs fixing violation one normal form also fixes violation higher normal form process also one table chosen normalization step meaning end example process might still tables satisfying highest normal form let database table following structure assume example book one author satisfy 1nf need ensure values column table atomic initial table subject contains set values meaning comply one way achieve first normal form would separate duplicities multiple columns although table formally complies 1nf atomic problem solution obvious book three subjects added database without altering structure solve problem elegant way necessary identify entities represented table separate respective tables case would result book subject publisher tables simply separating initial data multiple tables would break connection data means also need determine relationships newly introduced tables might noticed publisher id column book table foreign key realizing many-to-one relation book publisher book fit many subjects well subject may correspond many books means also need define many-to-many relationship achieve creating link table instead one table unnormalized form 4 tables conforming 1nf book table one candidate key compound key title format consider following table fragment attributes part key depend title price also depends format conform 2nf remove duplicities every non-key attribute must depend whole key part normalize table make title simple key every non-key attribute depends upon whole key remove price separate table dependency format preserved book table conforms 2nf table third normal form 3nf table 2nf transitive dependencies note book table rows previously omitted brevity genre id genre name depend upon primary key title independent one another dependency say genre name primary key deduced dependency genre name genre id genre id primary key since titles genres dependency introduces redundant data book table eliminated abstracting dependency genre name genre id table book table third normal form although tables 1nf definition normalized normalized commonly used mean 3nf eknf falls strictly 3nf bcnf n't much discussed literature intended “ capture salient qualities 3nf bcnf ” avoiding problems namely 3nf “ forgiving ” bcnf “ prone computational complexity ” since rarely mentioned literature included example information eknf see wikipedia page relational schema r considered boyce–codd normal form bcnf every one dependencies x → one following conditions hold true consider table 3nf previous step non-trivial dependency violating bcnf author → author nationality therefore table decomposed attribute represents fact key whole key nothing key therefore bcnf achieved assume database owned book retailer franchise several franchisees shops different locations therefore retailer decided add table contains data availability books different locations table structure consists compound primary key n't contain non-key attributes already bcnf therefore also satisfies previous normal forms however assume available books offered area might notice title unambiguously bound certain location therefore table n't satisfy 4nf means satisfy fourth normal form table needs decomposed well every record unambiguously identified superkey therefore 4nf satisfied suppose franchisees also order books different suppliers let relation also subject following constraint table 4nf supplier id equal join projections supplier id book book franchisee id franchisee id supplier id component join dependency superkey sole superkey entire heading table satisfy etnf decomposed decomposition compliance etnf ensured spot table satisfying 5nf usually necessary examine data thoroughly suppose table 4nf example little modification data let examine satisfies 5nf decompose table lower redundancies get following two tables happens try join tables query would return following data apparently join returns three rows let try add another table clarify relation end three separate tables join return actually possible join three tables means n't possible decompose franchisee book location without data loss therefore table already satisfies 5nf c.j date argued database 5nf truly normalized let look book table previous examples see satisfies domain key normal form logically thickness determined number pages means depends pages key let set example convention saying book 350 pages considered slim book 350 pages considered thick convention technically constraint neither domain constraint key constraint therefore rely domain constraints key constraints keep data integrity words nothing prevents us putting example thick book 50 pages makes table violate dknf solve create table holding enumeration defines thickness remove column original table way domain integrity violation eliminated table dknf simple intuitive definition sixth normal form table 6nf row contains primary key one attribute means example publishers table designed creating 1nf needs decomposed two tables normalization 6nf mostly used data warehouses benefits outweigh drawbacks
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Databases
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tcp delayed acknowledgment tcp delayed acknowledgment technique used implementations transmission control protocol effort improve network performance essence several ack responses may combined together single response reducing protocol overhead however circumstances technique reduce application performance described rfc 1122 host may delay sending ack response 500 ms. additionally stream full-sized incoming segments ack responses must sent every second segment delayed acks give application opportunity update tcp receive window also possibly send immediate response along ack certain protocols telnet delayed acks reduce number responses sent server factor 3 combining ack window update response data one segment additional wait time introduced delayed ack cause delays interacting certain applications configurations nagle algorithm used sending party data queued sender ack received sender send enough data fill maximum segment size example performs two small writes followed blocking read transfer pause ack delay timeout linux 2.4.4+ supports codice_1 socket option disables delayed ack example consider situation bob sending data carol bob socket layer less complete packet worth data remaining send per nagle algorithm sent receives ack data already sent time carol application layer send response gets data carol using delayed acks socket layer send ack timeout reached application transmitting data smaller chunks expecting periodic acknowledgment replies negative interaction occur prevent delay application layer needs continuously send data without waiting acknowledgment replies alternatively nagle algorithm may disabled application sending side
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Internet protocols
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stream control transmission protocol stream control transmission protocol sctp computer networking communications protocol operates transport layer serves role similar popular protocols tcp udp standardized ietf rfc 4960 sctp provides features udp tcp message-oriented like udp ensures reliable in-sequence transport messages congestion control like tcp differs protocols providing multi-homing redundant paths increase resilience reliability absence native sctp support operating systems possible tunnel sctp udp well map tcp api calls sctp calls existing applications use sctp without modification reference implementation released part freebsd version 7 since widely ported ietf signaling transport sigtran working group defined protocol number 132 year 2000 ietf transport area tsvwg working group maintains rfc 4960 defines protocol rfc 3286 provides introduction sctp applications submit data transmitted messages groups bytes sctp transport layer sctp places messages control information separate chunks data chunks control chunks identified chunk header protocol fragment message number data chunks data chunk contains data one user message sctp bundles chunks sctp packets sctp packet submitted internet protocol consists packet header sctp control chunks necessary followed sctp data chunks available one characterize sctp message-oriented meaning transports sequence messages group bytes rather transporting unbroken stream bytes tcp udp sctp sender sends message one operation exact message passed receiving application process one operation contrast tcp stream-oriented protocol transporting streams bytes reliably order however tcp allow receiver know many times sender application called tcp transport passing groups bytes sent sender tcp simply appends bytes queue bytes waiting go network rather keep queue individual separate outbound messages must preserved term multi-streaming refers capability sctp transmit several independent streams chunks parallel example transmitting web page images together web page text essence involves bundling several connections single sctp association operating messages chunks rather bytes tcp preserves byte order stream including byte sequence number segment sctp hand assigns sequence number message-id message sent stream allows independent ordering messages different streams however message ordering optional sctp receiving application may choose process messages order receipt instead order sending features sctp include designers sctp originally intended transport telephony signaling system 7 internet protocol goal duplicating reliability attributes ss7 signaling network ip ietf effort known sigtran meantime uses proposed example diameter protocol reliable server pooling rserpool tcp provided primary means transfer data reliably across internet however tcp imposed limitations several applications rfc 4960 adoption slowed lack awareness lack implementations particularly microsoft windows lack application support lack network support sctp provides redundant paths increase reliability sctp end point needs check reachability primary redundant addresses remote end point using heartbeat sctp end point needs acknowledge heartbeats receives remote end point sctp sends message remote address source interface decided routing table host sctp asymmetric multi homing one two end points support multi homing local multi homing remote single homing remote primary address reachable sctp association fails even alternate path possible sctp packet consists two basic sections chunk starts one byte type identifier 15 chunk types defined rfc 4960 least 5 defined additional rfcs eight flag bits two byte length field data compose remainder chunk chunk form multiple 4 bytes i.e. length multiple 4 padded zeros included chunk length two byte length field limits chunk 65,535 byte length including type flags length fields although encryption part original sctp design sctp designed features improved security 4-way handshake compared tcp 3-way handshake protect syn flooding attacks large cookies association verification authenticity reliability also key part security design sctp multihoming enables association stay open even routes interfaces particular importance sigtran carries ss7 ip network using sctp requires strong resilience link outages maintain telecommunication service even enduring network anomalies sctp sometimes good fingerprinting candidate operating systems ship sctp support enabled well known tcp udp sometimes overlooked firewall intrusion detection configurations thus often permitting probing traffic sctp reference implementation runs freebsd mac os x microsoft windows linux following operating systems implement sctp third-party drivers userspace library following applications implement sctp
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Internet protocols
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network operating system network operating system specialized operating system network device router switch firewall historically operating systems networking capabilities described network operating system allowed personal computers pcs participate computer networks shared file printer access within local area network lan description operating systems largely historical common operating systems include network stack support client–server model early microcomputer operating systems cp/m dos classic mac os designed one user one computer packet switching networks developed share hardware resources mainframe computer printer large expensive hard disk local area network technology became available two general approaches handle sharing resources networks arose historically network operating system operating system computer implemented network capabilities operating systems network stack allowed personal computers participate client-server architecture server enables multiple clients share resources printers early examples client-server operating systems shipped fully integrated network capabilities novell netware using internetwork packet exchange ipx network protocol windows server 2003 banyan vines used variant xerox network systems xns protocols peer-to-peer network operating systems also developed used networking capabilities share resources files located personal computers system based file server centralized management source peer-to-peer network sets connected computers equal share abilities use resources available network examples early peer-to-peer operating systems networking capabilities include appleshare used networking connecting apple products lantastic supporting dos microsoft windows os/2 computers well windows workgroups used networking peer-to-peer windows computers today distributed computing groupware applications become norm computer operating systems include networking stack matter course 1980s need integrate dissimilar computers network capabilities grew number networked devices grew rapidly partly allowed multi-vendor interoperability tcp/ip protocol suite became almost universally adopted network architectures therefore computer operating systems firmware network devices needed reliably support tcp/ip protocols network operating systems embedded router hardware firewall operates functions network layer layer 3 notable network operating systems include
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Operating systems
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bean validation bean validation defines metadata model api javabean validation metadata source annotations ability override extend meta-data use xml validation descriptors originally defined part java ee version 2 aims work java se apps well java bean validation jsr 303 originated framework approved jcp 16 november 2009 accepted part java ee 6 specification hibernate team provides hibernate validator reference implementation bean validation also created bean validation tck implementation jsr 303 needs pass bean validation 2.0 defined jsr 380 approved 2017-07-31 major release leverages language features java 8 useful purposes bean validation java 8 required minimum java version changes include bean validation 1.1 jsr 349 improves upon initial version 1.0 jsr 303 significant changes include final release 1.1 specification occurred 2013-05-24
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Programming language topics
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agbogbloshie agbogbloshie nickname commercial district korle lagoon odaw river near center accra ghana capital city near slum called old fadama agbogbloshie site became known destination locally generated automobile electronic scrap collected across city accra alleged center legal illegal exportation network environmental dumping electronic waste e-waste industrialized nations basel action network small ngo based seattle referred agbogbloshie digital dumping ground allege millions tons e-waste processed year however repeated international studies failed confirm allegations labelled e-waste hoax international reuse advocate wr3a exhaustive study trade used electronics nigeria funded unep basel convention revealed 540 000 tonnes informally processed waste electronics 52 material recovered according statistics world bank large cities like accra lagos majority households owned televisions computers decades un report weee africa 2012 disclosed majority used electronics found african dumps fact recently imported scrap originated african cities agbogbloshie situated banks korle lagoon northwest accra central business district roughly 40,000 ghanaians inhabit area migrants rural areas due harsh living conditions rampant crime area nicknamed sodom gomorrah basel convention prevents transfrontier shipment hazardous waste developed less developed countries however convention specifically allows export reuse repair annex ix b1110 numerous international press reports made reference allegations majority exports ghana dumped research us international trade commission found little evidence unprocessed e-waste shipped africa united states finding corroborated united nations environment programme mit memorial university arizona state university research 2013 original source allegation blaming foreign dumping material found agbogbloshie recanted rather stated never made claim 80 us e-waste exported whether domestically generated residents ghana imported concern remains methods waste processing especially burning emit toxic chemicals air land water exposure especially hazardous children toxins known inhibit development reproductive system nervous system especially brain concerns human health environment agbogbloshie continue raised area remains heavily polluted 2000s ghanaian government new funding loans implemented korle lagoon ecological restoration project klerp environmental remediation restoration project address pollution problem dredging lagoon odaw canal improve drainage flooding ocean 1960s slum area agbogbloshie wetland city accra urbanized ghetto grew referred old fadama ayaalolo 1980s ghetto place shelter refugees konkomba-nanumba war late 1990s newly available electricity akosombo dam led increased local demand electric electronic appliance consumption critics claim caused imbalanced shift electricity akosombo dam increased demand functional second-hand televisions computers imported west africa tech sector help ‘ bridge digital divide ’ ghanaians welcomed donations computers cost one-tenth price new one basel action network circulated claim 2008 much 75 percent second-hand electronics sent africa could reused ended landfills ban allegation slightly different 2002 claim 80 waste exporting harm 2002 became one cited references academic journals though documentation peer reviewed source documentation made available mapping e-waste controversy statements debates ii 2013 ban denied ever making claim ever stating statistic african imports local economy agbogbloshie based onion market serving immigrants accra greater tamale region dagbani north unemployed immigrants turned scrap metal collection including auto scrap supplement incomes electronic scrap processing fairly small activity market claim hundreds millions tons electronic waste imported area year reported several news sources considered experts utterly ridiculous preposterous united states definitely leading exporter e-waste ghana although imports arrive countries france germany korea switzerland netherlands multinational brands philips canon dell microsoft nokia siemens sony commonly found throughout waste according e-waste assessment studies refurbishing eee sales used eee important economic sector e.g alaba market lagos well-organized dynamic sector holds potential industrial development indirectly sector another important economic role supplies low middle income households affordable ict equipment eee view sector ’ positive socio-economic performance policy measures aiming improve e-waste management nigeria refrain undifferentiated banning second-hand imports refurbishing activities strive co-operative approach including market sector associations followers ban.org alleged non-governmental organizations ngos adding waste excess electronics donated intention helping scholarly institutions claim based 75 -80 orphaned waste statistic exporters must found numerous loopholes avoid legislation forbidding e-waste shipping labeling broken electronics ‘ end-of-life ’ ‘ second-hand-goods ’ falsely identifying working order true 50 75 electronics imported unable salvaged remain land import would illegal however un studies failed find evidence allegation source dumping statistic denied young men burning wires auto harnesses electronics subject several photojournal essays workers mostly young men disassemble cars appliances scrap electronics gathered wheeled push carts accra neighborhoods revenue recovery metals copper aluminum iron produce low wages several british news outlets made recycling workers cause celebre photographs workers burning old wire top tires plastic order melt plastic dismantling waste bare hands stones popularized press magnets electronics shown used gather smallest ferrous metal scraps remaining materials burned dumped nearby workers children adults alike sell metal scraps earn living half sack copper aluminium sell 700 ghana cedis amounting eight ten ghana cedis per day 4 6 usd population agbogbloshie consists economic migrants northern rural parts ghana living standards growing worse causing people move urban settings agbogbloshie conditions may significantly better making living easier inhabitants agbogbloshie live eat work relieve land amongst waste children able attend school often spend every evening weekend processing waste searching metals dwellings wooden shacks lack water sanitation area also home armed robbers prostitutes drug dealers others involved underground markets crime disease run rampant throughout agbogbloshie creating almost uninhabitable environment humans outsiders nicknamed area “ sodom gomorrah ” two condemned biblical cities due harsh living conditions agbogbloshie processing dumping electronic waste agbogbloshie polluting area creating serious environmental concern photographs agbogbloshie e-waste landfill show scrap workers burning wires auto harnesses plastic-encased electronics recover copper e-waste contains toxic chemicals emitted ground water atmosphere electronics broken burned processed poisons lead mercury arsenic dioxins furans brominated flame retardants seep surrounding soil water thereby seriously polluting landscape greenpeace lab tests shown water soil areas agbogbloshie revealed area contained concentrations chemicals levels hundred times allowable amount.several studies confirmed high levels lead soil particular risks workers children environmental lead contamination predominantly due burning plastic covering copper wires pvc insulation contains approximately 3000 mg/kg lead stiffener lead released burning guardian april 2019 reported study ipen basel action network found dangerous levels dioxins polychlorinated biphenyls pcbs chicken eggs agbogbloshie lead containing glass used computer monitors crt tubes also contributes elevated soil lead levels korle lagoon agbogbloshie situated extremely low levels dissolved oxygen result large uncontrolled quantities domestic industrial waste emitted water studies indicate entrance lagoon severely polluted suitable primary secondary contact due large amounts bacteria present processing electronic waste presents serious health threat workers agbogbloshie fumes released burning plastics metals used electronics composed highly toxic chemicals carcinogens workers often inhale lead cadmium dioxins furans phthalates brominated flame retardants.exposure fumes especially hazardous children toxins known inhibit development reproductive system nervous system brain particular similar e-waste processing areas conditions demographics like agbogbloshie 80 children dangerous levels lead blood inhabitants often suffer chronic nausea headaches chest respiratory problems high levels toxins also discovered soil food samples chemicals stay food chain e-waste presents potential security threat individuals exporting countries hard drives properly erased computer disposed reopened exposing sensitive information credit card numbers private financial data account information records online transactions accessed willing individuals organized criminals ghana commonly search drives information use local scams government contracts discovered hard drives found agbogbloshie multimillion-dollar agreements united states security institutions defense intelligence agency dia transportation security administration homeland security resurfaced agbogbloshie ghanaian government made effort restore area “ korle lagoon ecological restoration project ” klerp 2003 opec fund international development arab bank economic development africa kuwait fund arab economic development provided loan project expectation ghanaian government dredge lagoon restore surroundings goals project include reduction flooding increase marine life improvement water quality improvement general sanitary conditions due invasive nature project restoration efforts disputed inhabitants agbogbloshie klerp requires people leave area home majority squatters accra metropolitan assembly ama continually tried evict people met much resistance matter still dispute 2014 ngo pure earth formally blacksmith institute funded creation copper wire recycling center within agbogbloshie helped install several automated machines simplify removal plastic coating reduce burning efforts appear moderately successful however burning continues
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Computer security
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wdc 65c816 w65c816s also 65c816 65816 8/16-bit microprocessor mpu developed sold western design center wdc introduced 1983 w65c816s enhanced version wdc 65c02 8-bit mpu cmos enhancement venerable mos technology 6502 nmos mpu 65816 cpu apple iigs super nintendo entertainment system 65 part designation comes 65c02 compatibility mode 816 signifies mpu selectable 8– 16–bit register sizes addition availability 16 bit registers w65c816s features extended memory addressing 24-bits supporting 16 megabytes random-access memory enhanced instruction set 16 bit stack pointer well several new electrical signals improved system hardware management reset w65c816s starts emulation mode meaning substantially behaves 65c02 thereafter w65c816s may switched native mode two instruction sequence causing enable enhanced features yet still maintain substantial degree backward compatibility 65c02 software however unlike pdip40 version 65c02 pin-compatible replacement nmos ancestor pdip40 w65c816s pin-compatible 6502 family mpu related w65c816s w65c802 internal structure 16-bit support used 40-pin layout compatible original 6502 allowed used drop-in replacement certain roles lack new address pins limited 64 kb memory see extensive use longer produced 1981 bill mensch founder ceo wdc began development 65c02 production partners primarily rockwell semiconductor synertek primary goal 65c02 effort move original 6502 nmos process 65c02 cmos would allow run much lower power levels somewhere running clock speeds number new opcodes bug fixes also worked design development w65c816s commenced 1982 mensch consulted apple computer new version apple ii series personal computers would among things improved graphics sound apple wanted mpu would software compatible 6502 use apple ii ability address memory load store 16 bit words result 65c816 finished march 1984 samples provided apple atari second half year full release 1985 mensch aided design process sister kathryn responsible part device layout process also led 65c802 identical inside 65c816 produced fabrication lines diverged last metalization stages chip connected external pins 65c802 pins layout original 6502 allowed used drop-in replacement still allowing 16-bit processing cpu used however used original pinout 16 addressing pins could therefore access 64 kb external memory typically hardware manufacturers designed project ground used 65c816 rather 65c802 resulting latter withdrawn production apple subsequently integrated 65c816 apple iigs computer basic 65c816 design second-sourced gte sanyo others mid-to-late 1980s early 1990s 1990s 65c816 65c02 converted fully static core made possible completely stop processor clock without losing data registers feature along use asynchronous static ram made possible produce designs used minimal power standby state w65c816s available wdc 40 pin pdip plcc44 package well core asic integration example winbond w55v9x series tv edutainment ics wdc fabless semiconductor company works various foundries produce w65c816s well compatible products discrete processors available number electronics distributors designers wish include w65c816s functionality custom asic wdc offers rtl register-transfer level code verilog wdc 65816 features 65c816 two modes emulation mode 16-bit operations registers invisible chip appeared original 6502 cycle timings opcodes native mode made additional features visible cpu automatically returned emulation mode powered reset allowed drop-in replace 6502 obvious change 65c816 running 16-bit mode expansion various registers 8-bit 16-bit values affects accumulator x index registers stack pointer sp affect program counter p always 16-bit running native mode two bits status register change meaning original 6502 bits 4 5 used although bit 4 sometimes referred b reak flag native mode bit 4 becomes x flag bit 5 becomes flag bits control whether index registers x and/or accumulator/memory 8-bit 16-bit values zeros bits indicate 16-bit values ones indicate 8-bit values bits normally zero chip started remain switched native mode might immediately obvious one would want use 16-bit registers 8-bit mode switching 8-bit mode using new codice_1 set bit processor status codice_2 reset instructions means subsequent instructions accessing registers read single byte instead two instance bit set 1 codice_3 instruction issued single byte address 1234 read thereby reducing number cycles needed execute instruction particularly useful dealing 8-bit character data instance running 16-bit mode operations registers effect 16-bits instance left shift codice_4 shift 16 bits major change system running native mode memory model expanded 24-bit format original 16-bit format 6502 handled using 8-bit offset registers data bank register dbr program bank register pbr addresses code remain original 16-bit format values dbr pbr prepended form 24-bit address main memory means instructions access data within 64 kb page bank referred data outside page needs accessed dbr change likewise instructions lie anywhere memory using pbr branch jump instructions within bank addition register set direct page register set base address formerly called zero page referred direct page direct page offers special addressing mode requires one byte offer significantly improved performance used wisely 6502 direct page always first 256 bytes memory thus zero page whereas 16-bit register offset location 24-bit memory current mode operation stored emulation bit enough bits left status register hold new mode bit unique solution used mode bit left invisible unable directly accessed new codice_5 exchange carry emulation exchanges value emulation bit c arry bit bit 0 status register instance one wants enter native mode processor started one would use codice_6 clear carry bit codice_5 write emulation bit returning 6502 mode uses codice_8 cpu switches native mode upper 8-bits registers initially set zero read written complete 16-bit values point assuming x 16-bit mode system switches back 8-bit mode value upper 8-bits maintained return system switches back native systems based 65816 variants also used c-one supercpu enhancements commodore 64
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Computer architecture
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icmp hole punching icmp hole punching technique employed network address translator nat applications maintaining internet control message protocol icmp packet streams traverse nat nat traversal techniques typically required client-to-client networking applications internet involving hosts connected private networks especially peer-to-peer voice internet protocol voip deployments icmp hole punching establishes connectivity two hosts communicating across one network address translators either peer-to-peer client-server model typically third party hosts public transit network used establish udp tcp port states may used direct communications communicating hosts however icmp hole punching requires third party involvement pass information one nats exploiting nat loose acceptance inbound icmp time exceeded packets icmp time exceeded packet reaches destination nat arbitrary data packet expected nat allows packet reach destination server allowing destination server obtain client public ip address data stored packet client currently method icmp hole punching hole punching without third party involvement autonomous nat traversal developed samy kamkar january 22 2010 released open source software pwnat method later published ieee according paper proposed technique assumes client somehow learned current external globally routable ip address server nat key idea enabling server learn client's ip address server periodically send message fixed known ip address simplest approach uses icmp echo request messages unallocated ip address 1.2.3.4 since 1.2.3.4 allocated icmp request routed routers without default route icmp destination unreachable messages may created routers ignored server result messages sent 1.2.3.4 nat enable routing replies response request connecting client fake reply specifically client transmit icmp message indicating ttl_expired message could legitimately transmitted internet router sender address would expected match server target ip server listens fake icmp replies upon receipt initiates connection sender ip specified icmp reply
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Computer security
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php license php license software license php scripting language released php license designed encourage widespread adoption source code redistribution permitted source binary form without modifications caveats version 3 php used dual license—php 3 source available either php license gnu general public license gpl practice discontinued php 4 php developers citing restrictions reuse associated gpl copyleft enforcement reason dropping zend engine core php interpreter separately licensed similar zend engine license contains similar naming restrictions php license applying names zend zend engine clause requiring advertising materials mention use php license open source license according open source initiative non-copyleft free software license according free software foundation license gpl-incompatible due restrictions usage term php debian maintainers long-standing discussion since least 2005 validity php license expressed concerns include license contains statements software covers specific distributing php software php therefore would false statements
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Programming language topics
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usenix annual technical conference usenix annual technical conference usenix atc canonically usenix conference computing professions sponsored usenix association conference includes computing tutorials single track technical session presenting refereed research papers sig meetings bofs several notable announcements talks usenix 1995 james gosling announced oak become java programming language john ousterhout first presented tcl usenet announced considered one prestigious operating systems venues rating australian ranking ict conferences era prior 1995 two usenix technical conferences held year one held summer winter
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Operating systems
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clipper architecture clipper architecture 32-bit risc-like instruction set architecture designed fairchild semiconductor architecture never enjoyed much market success computer manufacturers create major product lines using clipper processors intergraph high level hardware first processors using clipper architecture designed sold fairchild division responsible subsequently sold intergraph 1987 intergraph continued work clipper processors use systems clipper architecture used simplified instruction set compared earlier cisc architectures incorporate complicated instructions present contemporary risc processors instructions implemented so-called macro instruction rom within clipper cpu scheme allowed clipper somewhat higher code density risc cpus initial clipper microprocessor produced fairchild c100 became available 1986 followed faster c300 intergraph 1988 final model clipper c400 released 1990 extensively redesigned faster added floating-point registers c400 processor combined two key architectural techniques achieve new level performance — superscalar instruction dispatch superpipelined operation many processors time used either superscalar instruction dispatch superpipelined operation clipper c400 first processor use intergraph started work subsequent clipper processor design known c5 never completed released nonetheless advanced processor design techniques devised c5 intergraph granted patents patents along original clipper patents basis patent-infringement lawsuits intergraph intel companies unlike many microprocessors clipper processors actually sets several distinct chips c100 c300 consist three chips one central processing unit containing integer unit floating point unit two cache memory management units cammus one responsible data one instructions cammus contained caches translation lookaside buffers support memory protection virtual memory c400 consists four basic units integer cpu fpu mmu cache unit initial version used one chip cpu fpu discrete elements mmu cache unit later versions mmu cache unit combined one cammu chip clipper 16 integer registers r15 used stack pointer 16 floating-point registers limited 8 early implementations plus program counter pc processor status word psw containing alu fpu status flags trap enables system status word ssw containing external interrupt enable user/supervisor mode address translation control bits user supervisor mode separate banks integer registers interrupt handling consisted saving pc psw ssw stack clearing psw loading pc ssw memory trap vector clipper load/store architecture arithmetic operations could specify register immediate operands basic instruction parcel 16 bits 8 bits opcode 4 bits source register 4 bits destination register immediate-operand forms allowed 1 2 following instruction parcels specify 16-bit sign-extended 32-bit immediate operand processor uniformly little-endian including immediate operands special quick encoding 4-bit unsigned operand provided add subtract load move quick register move complement quick register addressing modes load/store branch instructions follows displacements sign-extended addition usual logical arithmetic operations processor supported complex macro instructions allowed instructions allowed arbitrary stack pointer register specified except user register save/restore multiple-register operations could use r15 intergraph sold several generations clipper systems including servers workstations systems included interact interserve interpro product lines targeted largely cad market fairchild promoted clix operating system version unix system v use clipper intergraph adopted clix clipper-based systems continued develop operating system available systems intergraph work version microsoft windows nt clipper systems publicly demonstrated effort canceled release intergraph decided discontinue clipper line began selling x86 systems windows nt instead
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Computer architecture
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geary e-mail client geary free open-source email client written vala based webkitgtk although since adopted gnome project originally developed yorba foundation purpose e-mail client according adam dingle yorba founder bring back users online webmails faster easier use desktop application pantheon mail fork initiated elementary os community demise yorba though point decided rewrite scratch remaining references geary pantheon code base translations implementation support gpg started still incomplete 2019 geary internally uses sqlite database store local copy emails indexing uses fully asynchronous gobject-based imap client library one feature distinguishes geary open source email clients focus conversation view geary pantheon mail using gettext translations pantheon mail migrated webkitgtk+2 yet developers decided first migrate code managing conversation view use native gtk widgets gtk.css granite gtk+ library used part elementary os offered several advantages including minimizing use webviews reducing code supporting hardware accelerated animations supporting rtl languages also removed use custom gtk bars like codice_5 making code complicated difficult read geary uses webkit2 since least version 3.32.0 historically elementary os directly supported project geary became default application gnu/linux distribution march 25 2013 jim nelson executive director yorba launched crowdfunding campaign indiegogo gather us 100,000 would used pay 3 full-time yorba engineers working time geary unfortunately april 23 2013 us 50,860 gathered 1,192 backers amount met campaign failed according rules set indiegogo yorba receive money pledged failure jim nelson declared blog post crowdfunding campaign kind experiment see route enough sustain open-source development reaffirmed geary created improve linux experience therefore chance ported os x windows platforms yorba foundation stopped activities gnome announced plans project time future geary unclear result uncertainties due previous design disagreements old geary team elementary os actually using geary default mail client though heavily patched version daniel foré leader elementary os decided fork project continue development fork project renamed pantheon mail process pantheon mail replaced geary elementary os 0.4 codenamed loki march 2016 michael gratton applied become new maintainer geary main goal try fixing pressing issues like dependency old webkit1gtk collaboration pantheon mail better support non-gmail servers mailbox management account ui extending search etc contributing geary gnome project requires maintainer become gnome member discussion adam dingle yorba founder agreed wait gratton fulfill gnome membership application requirements meantime gratton post patches gnome bugzilla instance adam commit version 0.11 released version 0.13 released february 18 2019 shortly afterwards version scheme changed match gnome release schedule current geary version 3.32 initial name geary coincides name geary street yorba products named streets san francisco however according former yorba employee application named address yorba foundation located actually coincidence first beta geary released may 2012 yorba still located capp street time
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Internet protocols
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nyc mesh nyc mesh physical network interconnected routers group enthusiasts working support expansion project freely accessible open wireless community network nyc mesh internet service provider isp although connect internet offer internet access service members network includes 200 active member nodes throughout five boroughs concentrations users lower manhattan brooklyn goal nyc mesh build large scale decentralized digital network owned run eventually cover new york city neighboring urban areas participation project governed network commons license agreement partially modeled similar license use guifi.net lists four key tenets similar projects include freifunk germany ninux italy sarantaporo.gr greece people open network oakland ca red hook wi-fi brooklyn ny like many free community-driven networks nyc mesh uses mesh technology facilitate robustness resiliency additionally larger nodes project uses border gateway protocol bgp nodes connected via wifi links similar used wireless routers homes powerful routers able function backbone making connections distances mile nyc mesh founded 2012 originally based cjdns protocol 2015 project received grant isoc-ny new york chapter internet society nyc mesh connects internet via de-cix internet exchange point ixp first super node sabey data center 375 pearl street project received membership boost due u.s. federal communications commission vote december 2017 repeal 2015 net neutrality rules coinciding decision average number member sign-ups requests per month jumped 20 400
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Distributed computing architecture
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freescale dragonball motorola/freescale semiconductor dragonball mc68328 microcontroller design based famous 68000 core implemented all-in-one low-power system handheld computer use supported μclinux designed motorola hong kong released 1995 dragonball major design win earlier versions palm computing platform however palm os 5 onwards superseded arm-based processors texas instruments intel processor also used alphasmart line portable word processors examples include dana dana wireless processor capable speeds 16.58 mhz run 2.7 mips million instructions per second base 68328 dragonball ez mc68ez328 model extended 33 mhz 5.4 mips dragonball vz mc68vz328 model 66 mhz 10.8 mips dragonball super vz mc68sz328 32-bit processor 32-bit internal external address bus 24-bit external address bus ez vz variants 32-bit data bus many built-in functions like color grayscale display controller pc speaker sound serial port uart irda support uart bootstrap real time clock able directly access dram flash rom mask rom built-in support touch screens all-in-one computer chip dragonball ez palm handhelds twice many ics recent dragonball mx series microcontrollers later renamed freescale i.mx mc9328mx/mcimx series intended similar application earlier dragonball devices based arm processor core instead 68000 core
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Computer architecture
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list dns record types list dns record types overview resource records rrs permissible zone files domain name system dns also contains pseudo-rrs types records simply provide types information example hinfo record gives description type computer/os host uses others return data used experimental features type field also used protocol various operations progress rendered originally defined record-types obsolete records listed iana limited use various reasons marked obsolete list obscure services older versions services special notes saying right
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Internet protocols
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real data transport real data transport rdt proprietary transport protocol actual audio-video data developed realnetworks 1990s commonly used companion control protocol streaming media like ietf real time streaming protocol rtsp non-proprietary alternative rdt ietf real-time transport protocol rtp also implemented realnetworks players reported 2002 book firewalls rdt used two unidirectional udp connections one data sent server client another opposite direction retransmission requests book reported realnetworks g2 server used rdt configuration default another 2003 book reported rdt also seen carried transmission control protocol tcp fall-back mechanism rdt included part helix community project
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Internet protocols
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dizzy rapids dizzy rapids arcade style action video game published 1991 codemasters amstrad cpc spectrum dos atari st commodore 64 amiga developed harmony gold tatsunoko production published 1993 toshiba miramax communications msx2 game involves dizzy riding barrels river avoiding obstacles enemies another game derived minigame game found fantastic adventures dizzy like bubble dizzy game based game play arcade game titled toobin c64 version developed first paul black c64 version originally clone toobin called 'toobin turles game taken codemasters consideration rebranded take advantage dizzy character
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Computer architecture
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cert c coding standard sei cert c coding standard software coding standard c programming language developed cert coordination center improve safety reliability security software systems guidelines cert c secure coding standard cross-referenced several standards including common weakness enumeration cwe entries misra
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Computer security
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programming language reference programming language reference language reference manual artifact describes programming language users developers understand basic elements write computer programs target language programming language reference manual one form documentation associated mainstream programming languages reference manual ordinarily separate distinct programming language specification usually detailed intended use implementors language rather simply use language accomplish processing task
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Programming language topics
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netgear wnr3500l wnr3500l also known wnr3500u 802.11b/g/n wi-fi router created netgear officially launched autumn 2009 wnr3500l runs open-source linux firmware supports installation third party packages dd-wrt tomato version 1 version 2 several ways identify version including v2 label version 2 version 1 version 2 according one analysis installing dd-wrt reduced performance
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Operating systems
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ping flood ping flood simple denial-of-service attack attacker overwhelms victim icmp echo request ping packets effective using flood option ping sends icmp packets fast possible without waiting replies implementations ping require user privileged order specify flood option successful attacker bandwidth victim instance attacker dsl line victim dial-up modem attacker hopes victim respond icmp echo reply packets thus consuming outgoing bandwidth well incoming bandwidth target system slow enough possible consume enough cpu cycles user notice significant slowdown flood ping also used diagnostic network packet loss throughput issues
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Computer security
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apulet apulet plural apulettes component cell computer architecture consisting bundle comprising data object code necessary perform action upon cell architecture calls several apus attached processing units primary processing system control single processing element pe apu loaded apulet pe pass results next apu
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Computer architecture
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national strategy trusted identities cyberspace national strategy trusted identities cyberspace nstic us government initiative announced april 2011 improve privacy security convenience sensitive online transactions collaborative efforts private sector advocacy groups government agencies organizations strategy imagined online environment individuals organizations trust identify authenticate digital identities digital identities organizations devices promoted offer mandate stronger identification authentication protecting privacy limiting amount information individuals must disclose strategy developed input private sector lobbyists including organizations representing 18 business groups 70 nonprofit federal advisory groups comments dialogue public strategy four guiding principles nstic described vision compared ecosystem individuals businesses organizations enjoy greater trust security conduct sensitive transactions online technologies policies agreed upon standards would securely support transactions ranging anonymous fully authenticated low high value imagined world implementation included three initiatives nstic announced presidency barack obama near end first term april 15 2011 magazine article said individuals might validate identities securely sensitive transactions banking viewing health records let stay anonymous blogging surfing web january 2011 u.s. department commerce established national program office npo led national institute standards technology help implement nstic coordinate implementation activities federal agencies npo works white house cybersecurity coordinator originally howard schmidt 2012 michael daniel nstic called steering group led private sector administer development adoption framework identity ecosystem steering group idesg held meeting chicago august 15–16 2012 meeting brought together 195 members person 315 members remotely additional plenary meetings phoenix arizona santa clara california boston massachusetts grant 2012 2014 trusted federal systems inc. group administrative body federal government initiated supported pilot programs 2012 nstic awarded 9 million pilot projects first year example american association motor vehicle administrators developing demonstration commercial identity provider credentials virginia state government including securely verifying identities online virginia department motor vehicles internet2 received 1.8 million research id.me given two-year grant 2013 work funded nist trusted identities group web page nstic called u.s. federal government agencies early adopters identity ecosystem envisioned nstic agencies struggled implement services provide internally externally technical policy cost barriers made challenging accept third-party credential providers accredited federal identity credential access management ficam initiative response white house created federal cloud credential exchange fccx team co-chaired nstic general services administration team consisted representatives agencies whose applications accessed large population external customers november 2012 united states postal service chosen manage pilot version fccx awarded contract build securekey technologies member fido alliance contract renewed may 2015 connect.gov launched december 2014 manifestation pilot first two companies provide individual us citizens identity management services compatible connect.gov id.me verizon ping identity forgerock first software platforms provide ficam-compliant credentials enable private sector organizations connect securely government agencies primary objective project may 10 2016 18f announced blog entry connect.gov would replaced replacement system would called login.gov launched april 2017 identity ecosystem steering group idesg received start funding nist 2010 since created series documents available web site 2016 introduced identity ecosystem framework idef registry self-assessment proposal generated criticism since released draft form june 2010 much centered around privacy implications proposal shortly draft release electronic privacy information center epic consumer-rights civil liberties organizations sent committee statement response draft nstic policy requesting clearer complete plan create safeguard internet users rights privacy epic head marc rotenberg called nstic historic also cautioned ... online identity complex problem risk 'cyber-identity theft consolidated identity systems real us need protect online privacy nstic addressed early privacy concerns 2013 fair information practice principles document subsequent initiatives sought advance privacy example american civil liberties union electronic frontier foundation involved privacy committee idesg
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Computer security
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timer coalescing timer coalescing computer system energy-saving technique reduces central processing unit cpu power consumption reducing precision software timers allow synchronization process wake-ups minimizing number times cpu forced perform relatively power-costly operation entering exiting idle states
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Computer architecture
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zpu microprocessor zpu microprocessor stack machine designed norwegian company zylin run supervisory code electronic systems include field-programmable gate array fpga zpu relatively recent stack machine small economic niche growing number users implementations designed require small amounts electronic logic making electronic logic available purposes fpga make easily usable port gnu compiler collection makes much easier apply cpus without compilers sacrificing speed exchange small size keeps intermediate results calculations memory push-down stack rather registers zylin corp. made zpu open-source 2008 many electronic projects include electronic logic fpga wasteful also microprocessor commonplace add cpu electronic logic fpga often smaller less-expensive fpga could used cpu used less resources exact situation zpu designed address zpu designed handle miscellaneous tasks system best handled software example user interface zpu slow small size helps place needed high-speed algorithm fpga another issue cpus fpgas closed-source available particular maker fpgas occasionally project needs design widely distributed security inspections educational uses reasons licenses proprietary cpus prevent uses zpu open-sourced projects need code must small run cpu inherently larger code alternatively project may benefit wide selection code compilers debugging tools gnu compiler collection cases emulator written implement zpu instruction set target cpu zpu compilers used produce code resulting system slow packs code less memory many cpus enables project use wide variety compilers code zpu designed explicitly minimize amount electronic logic minimal instruction set yet encoded gnu compiler collection also minimizes number registers must fpga minimizing number flip-flops instead registers intermediate results kept stack memory also small code saving memory stack machine instructions need contain register ids zpu code smaller risc cpus said need 80 space arm holdings thumb2 example signed immediate helps zpu store 32-bit value 5 bytes instruction space little one risc cpus require least eight bytes finally 2/3 instructions emulated firmware implemented using 1/3 required instructions although result slow resulting cpu require little 446 lookup-tables measure fpga complexity roughly equivalent 1700 electronic logic gates zpu reset vector consisting 32-bytes code space starting location zero also single edge-sensitive interrupt vector consisting 32 bytes code space beginning address 32 vectors 2 63 32 bytes space reserved code emulate instructions 33 63 base zpu 32-bit data path zpu also variant 16-bit-wide data path save even logic zpu well-tested port gnu compiler collection enthusiasts firmware engineers ported ecos freertos μclinux least one group enthusiasts copied popular development environment arduino adapted zpu multiple models zpu core besides original zylin cores also zpuino cores zpuflex core zylin core designed minimal fpga footprint includes 16-bit version zpuino practical improvements speed replace emulated instructions hardware embedded system-on-chip framework zpuflex designed use external memory blocks replace emulated instructions hardware academic projects include power efficiency studies improvements reliability studies improve speed implementors implemented emulated instructions added stack cache beyond one implementor said two-stack architecture would permit pipelining i.e improving speed one instruction per clock cycle might also require compiler changes one implementor reduced power usage 46 stack cache automated insertion clock gating power usage roughly equivalent small open-source amber core implements arm v2a architecture parts zpu would aided fault-tolerance address bus stack pointer program counter tos abbreviation top stack nos abbreviation next top stack code points 33 63 may emulated code vectors 2 32 loadh storeh 16-bit memory access lessthan comparisons set 1 true 0 false lessthanorequal ulessthan ulessthanorequal swap tos nos mult lshiftright ashiftleft ashiftright call eq neq neg sub xor loadb storeb 8-bit memory access div mod eqbranch neqbranch poppcrel config pushpc syscall pushspadd halfmult callpcrel
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Computer architecture
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bruce lee video game bruce lee video game designed ron j. fortier graphics kelly day music john a. fitzpatrick originally developed atari 8-bit family published 1984 datasoft along ports apple ii commodore 64 bruce lee platform game hybrid player controls bruce lee second player controls either yamo alternates player one control bruce lee game converted zx spectrum amstrad cpc published u.s. gold msx version published 1985 comptiq plot involves eponymous martial artist advancing chamber chamber wizard tower seeking claim infinite wealth secret immortality twenty chambers represented single screen platforms ladders progress player must collect number lanterns suspended various points chamber chambers guarded two mobile enemies ninja attacks bokken stick green yamo large unarmed warrior visually styled sumo wrestler attacking punches crushing kicks platforms sufficient graphics support yamo skin actually pictured green though cover art natural human skin tone multiplayer mode allows second player control yamo allow two players alternately control bruce player playing yamo inactive certain time computer takes ninja yamo also vulnerable screen dangers infinite lives always return whereas yamo consistently identified single person one version manual implies reappearance ninja new individual replacing previous one later chambers include hazards mines moving walls well comb-like surface electric spark racing along skilful walking climbing ducking jumping required negotiate twentieth screen lee finally faces evil fire wizard zx spectrum version bruce lee received enthusiastic reviews computer gaming world stated game delivers foot kicking kick jabbing quick ducking action-packed adventure 'd expect good grade b martial arts movie crash magazine awarded 91 highlighting zesty graphics enjoyable fighting action addictivity sinclair user also found game enjoyable awarding 4 5 stars felt sound underused larger variety tasks could included spectrum critical pointing takes games complete 20 chambers 1990 retrospective sinclair found bruce lee still easy complete graphics aged well addition felt fighting moves available player lacked impact limited beat 'em however described historically important game first combine platform/collection beat 'em 'up genres home computing weekly praised graphics movement september 9 2018 speedrun game completion time 5m42s recorded zx spectrum via youtube livestream using original 128k model accepted speedrun.com fastest completion runs games located speedrun also available see youtube game included 1986 compilation sold million ii along match point match day knight lore
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Computer architecture
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eggdrop eggdrop popular irc bot oldest still maintained originally written robey pointer december 1993 help manage protect efnet channel gayteen one eggdrop bot version named valis eggdrop originally intended help manage protect channels takeover attempts forms irc war bot written c programming language features interfaces c modules tcl scripts allow users enhance functionality bot large number tcl scripts available expand bot functionality written eggdrop users scripts available add extend support online games stats user channel management information storage lookup greeting channel members tracking last seen times botnet management anti-spam file serving distribution usually via dcc protocol irc services similar chanserv nickserv much eggdrop includes built-in support sharing user information channel bans however script required simultaneously control multiple bots bots coordinate channel management modes bot also features botnet allows multiple bots linked together share data act coordinated fashion botnet supports party line accessible via dcc chat telnet people communicate within botnet various channels equivalent miniature irc channel 0 default referred party line years eggdrop become one popular bots run irc users
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Internet protocols
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operating system projects osp environment operating system projects teaching operating system designed provide environment introductory course operating systems selectively omitting specific modules operating system students re-implement missing functionality instructor generate projects require students understand fundamental operating system concepts distribution includes osp project generator used package project produce stubs files empty except required components compiled files students must implement osp includes simulator student code runs
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Operating systems
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blue frog blue frog freely-licensed anti-spam tool produced blue security inc. operated part community-based system tried persuade spammers remove community members addresses mailing lists automating complaint process user spam received blue security maintained addresses hashed form intrude registry spammers could use free tools clean lists tool discontinued community members reported spam blue security analyzed make sure met guidelines reported sites sending illegal spam isps hosted could contacted willing work anti-spam groups law-enforcement authorities attempt get spammer cease desist measures failed blue security sent back set instructions blue frog client client software used instructions visit leave complaints websites advertised spam messages spam message user received blue frog client would leave one generic complaint including instructions remove blue security users future mailings blue security operated assumption community grew flow complaints tens hundreds thousands computers would apply enough pressure spammers clients convince stop spamming members blue security community blue frog software included firefox internet explorer plugin allowing gmail hotmail yahoo mail e-mail users report spam automatically users could also report spam desktop email applications microsoft office outlook outlook express mozilla thunderbird users downloaded free blue frog software registered e-mail addresses intrude registry user could protect ten addresses one personal dns domain name blue frog available free add-on within firetrust mailwasher anti-spam filter also compatible spamcop tool different spam-fighting methods blue security released software products including blue frog open-source developer community could review modify enhance may 1 2006 blue frog members started receive intimidating e-mail messages sources claiming software actually collecting personal details identity theft ddos attacks creating spam database purposes blue security contested claims may 2006 blue security company subject retaliatory ddos attack initiated spammers servers folded load blue security redirected dns entries point company weblog announcing difficulty company weblog hosted blogs.com webportal subsidiary six apart effectively redirected attack blogs.com caused six apart server farm collapse turn said made 2,000 blogs unreachable several hours individuals claiming members computer security establishment condemned blue security company action took ddos attack representative renesys likened action pushing burning couch house neighbor defense blue security inc. stated aware ddos attack made dns change claiming blackholed isolated israeli network result social engineering hack alleged pulled one attackers high-tier isp tech support staff claim disputed many writers todd underwood writer renesys blog sources however agree regardless whether blue security blackholed seem facing attack time redirected web address blue security also claimed remained amicable terms six apart pointed fact blog hosting company blame even name press release explained service outage event action widely reported security websites possibly damaging blue security reputation within community time incident broad reporting general-interest media considered many boon notoriety blue security blue frog project security expert brian krebs gives different reason blue security website unavailable article washington post says happened blue security lying unable receive http requests servers saying black hole filtered maliciously re-directed traffic rather actually unable receive traffic due attack dns servers makes probable essentially telling truth ceo eran reshef simply misinformed users unable reach site users accused blue frog malware mozilla chat forums claiming blue frog spammed signatures yahoo gmail accounts left active remnants operating system uninstalling hinted actual reason blue frog existence accumulating do-not-spam database harvest fresh addresses spammers deluge blue frog shut one week forum thread appeared blue security recast collactive would accused spamming soon attack started blue security ceo eran reshef claimed identified attacker pharmamaster quoted writing blue found right solution stop spam ca n't let continue icq conversation blue security prime suspects distributed denial service ddos attack blue security servers identified rokso database christopher brown aka swank aka dollar partner joshua burch aka zmack unidentified australians russians russian/americans notably leo kuvayev alex blood also involved suspects identified transcript postings special ham forum spam attacks ddos attack planned blue security ceased operation may 16 2006 company announced look non-spam related uses technology company investors expressed full support company decision change business plan many users suggested continuing project goals decentralized manner specifically using peer-to-peer technology client distributed via bittorrent similar thus making spam processing client distribution elements harder spammers attack one program purportedly begun name okopipi though appears abandoned number users recommended users uninstall blue frog program longer useful without blue security servers active one former blue security members red dwarf wrote program called complainterator runs windows add-on several popular email clients processes spam emails produces email messages sent sites hosting spamvertised products goal inform hosting sites hopes remove spam sites thereby making difficult spammers profit spam activities
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Computer security
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plymouth software plymouth bootsplash linux supporting animations using direct rendering manager drm kms driver gets packed initrd besides eye-candy plymouth also handles user interaction boot plymouth first included fedora 10 cambridge shipped november 25 2008 replaced red hat graphical boot rhgb ubuntu includes ubuntu 10.04 lts lucid lynx release shipped april 29 2010 mandriva switched splashy plymouth version adélie 2010.0
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Operating systems
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gambit scheme implementation gambit also called gambit-c programming language variant language family lisp variants named scheme gambit implementation consists scheme interpreter compiler compiles scheme language c makes cross-platform software conforms standards rrs rrs institute electrical electronics engineers ieee several scheme requests implementations srfis gambit released first 1988 gambit-c gambit c backend released first 1994 free open-source software released gnu lesser general public license lgpl 2.1 apache license 2.0 compiling intermediate representation case portable c chicken bigloo programs written gambit compiled common popular operating systems linux macos unix-like systems windows gerbil scheme variant scheme implemented gambit-c supports current r*rs standards common srfis state art macro module system inspired racket language termite scheme variant scheme implemented gambit-c. termite intended distributed computing offers simple powerful message passing model concurrency inspired erlang gambit compiler produces c code full integration support c++ objective-c compilers gnu compiler collection gcc thus software written gambit-c contain c++ objective-c code fully integrate corresponding libraries
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Programming language topics
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i/o kit i/o kit written iokit source code sometimes elsewhere open-source framework xnu kernel helps developers code device drivers apple macos ios operating systems i/o kit framework evolved nextstep driverkit shared similarities either mac os 9 device driver framework bsd i/o kit framework implemented subset c++ omits features apple feels unsafe use multithreaded kernel exceptions multiple inheritance templates run-time type information embedded c++ chosen partly apple believed developers would comfortable writing drivers commonly used language objective-c still providing object-oriented framework allowing device driver developers focus coding features specific hardware instead reimplementing features common given device addition providing common code device drivers framework also provides power management driver stacking automatic configuration dynamic loading drivers
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Operating systems
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constrained shortest path first constrained shortest path first cspf extension shortest path algorithms path computed using cspf shortest path fulfilling set constraints simply means runs shortest path algorithm pruning links violate given set constraints constraint could minimum bandwidth required per link also known bandwidth guaranteed constraint end-to-end delay maximum number links traversed include/exclude nodes cspf widely used mpls traffic engineering routing using cspf known constraint based routing cbr path computed using cspf could exactly computed ospf is-is could completely different depending set constraints met consider network right route computed router-a router-c satisfying bandwidth constrained x- units link cost link based hop-count i.e. 1 x 50 units cspf give path → b → c. x 55 units cspf give path → → e → c. x 90 units cspf give path → → e → f → c. cases ospf is-is result path → b → c. however link costs topology different cspf may accordingly determine different path example suppose hop count used link cost links → b b → c cost 4 case x 50 units cspf give path → → e → c. x 55 units cspf give path → → e → c. x 90 units cspf give path → → e → f → c
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Internet protocols
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wtx form factor wtx workstation technology extended motherboard form factor specification introduced intel idf september 1998 use high-end multiprocessor multiple-hard-disk servers workstations specification support major oems compaq dell fujitsu gateway hewlett-packard ibm intergraph nec siemens nixdorf umax motherboard manufacturers acer asus supermicro tyan updated 1.1 february 1999. specification discontinued url www.wtx.org longer hosts website owned intel since least 2004 form factor geared specifically towards needs high-end systems included specifications wtx power supply unit psu using two wtx-specific 24-pin 22-pin molex connectors wtx specification created standardize new motherboard chassis form factor fix relative processor location allow high volume airflow portion chassis processors positioned allowed standard form factor motherboards chassis used integrate processors demanding thermal management requirements bigger atx maximum wtx motherboard size intended provide room order accommodate higher numbers integrated components wtx computer cases backwards compatible atx motherboards vice versa sometimes came equipped atx power supplies
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Computer architecture
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application kit application kit usually called appkit graphical user interface toolkit macos comprises collection objective-c classes protocols used build application mac classes also used swift objective-c bridge xcode built-in functionality developing cocoa application using appkit including ability visually design user interfaces interface builder appkit along foundation core data part cocoa accordingly relies heavily patterns like reference types delegation notifications target–action model–view–controller applications bundled macos—for example finder textedit calendar preview–use appkit provide user interface appkit primarily associated macos originally developed use nextstep later openstep foundation classes protocols still use “ ns ” prefix result heritage open-source clone appkit maintained part gnustep various unix-based oses ios tvos use framework called uikit derived appkit uses many similar structures 170 classes included application kit following classes form core
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Operating systems
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pac-man development game began april 1979 directed toru iwatani nine-man team iwatani wanted create game could appeal women well men video games time war- sports-themed although inspiration pac-man character reportedly image pizza slice removed iwatani said also rounded japanese symbol kuchi meaning mouth in-game characters made cute colorful appeal younger players original japanese title puckman derived titular character hockey-puck shape pac-man widespread critical commercial success game important influential commonly listed one greatest video games time success game led several sequels merchandise two television series well hit single buckner garcia pac-man video game franchise remains one highest-grossing best-selling game series time generating 14 billion revenue 43 million sales combined character pac-man mascot flagship icon bandai namco entertainment highest brand awareness video game character north america player navigates pac-man maze dead ends maze filled pac-dots includes four roving multi-colored ghosts blinky pinky inky clyde passageway left side screen right side one energizer four quadrants bonus fruits appear level objective game accumulate many points possible eating dots fruits blue ghosts dots stage eaten stage completed player advance next stages one three intermission animations plays four ghosts roam maze chase pac-man ghosts touches pac-man life lost lives lost game player begins three lives dip switches machine change number starting lives one two five player receive one extra life bonus obtaining 10,000 points number points needed bonus life changed 15,000 20,000 disabled altogether near corners maze four flashing energizers allow pac-man eat ghosts earn bonus points enemies turn deep blue reverse direction move away pac-man usually move slowly enemy eaten eyes return center ghost box ghost regenerated normal color bonus score earned eating blue ghost increases exponentially consecutive ghost eaten single energizer active score 200 points scored eating one ghost 400 eating second ghost 800 third 1600 fourth cycle restarts 200 points pac-man eats next energizer blue enemies flash white signal return normal color become dangerous length time enemies remain vulnerable varies one stage next generally becoming shorter game progresses later stages enemies begin flashing immediately energizer consumed without solid-blue phase starting stage nineteen ghosts become edible still reverse direction fruits appear twice per level directly center ghost box eating one gives 100 5,000 points table lists stage type value fruit appears long ghosts blue energizer eaten many times ghosts flash returning normal enemies pac-man known alternately monsters ghosts creator toru iwatani designed enemy distinct personality keep game becoming impossibly difficult boring play iwatani described enemy behaviors detail 2011 game developers conference red enemy simply chases pac-man pink enemy aims position front pac-man mouth blue enemy seek position similar fixed spot pink enemy practice however blue enemy behave like three enemies although iwatani claimed orange enemy behavior random alternates behaving like red enemy distance pac-man moving towards lower-left corner maze whenever gets close pac-man designed ending however level 256 bug corrupts entire right half maze seemingly random symbols tiles overwriting values edible dots makes impossible eat enough dots complete level serving effectively final level known split screen bug caused calculation number fruit draw rolling zero code attempts draw 256 fruit 236 designed resulting maze corrupted tilemap holds fruits 20 elements long arranged three cases case handles levels less seven case b handles levels 8–19 case c handles level 19 game reaches level 256 level counter overflows back 0 thus level 256 treated level 0 game executes case rather case c level number less seven algorithm draws fruits continues draw fruit till fruit number level number match upon reaching fruit number 255 fruit number overflows back 0 matching level number 256 fruit drawn game draws first 13 fruit issues upon reaching fruit number 14 begins draw fruit right side map game reaches 20th entry fruit table game longer draw fruit still 236 fruit needs draw thus game begins draw pieces tile map onto screen substitute 236 extra fruit pac-man move pieces act like walls 256 fruit drawn game draws 7 extra blank spaces final fruit level impossible beat using one game player needs eat 244 dots move next level dots overwritten tilemap nine dots hidden within glitch screen re-spawn player dies maximum five extra lives limits number dots 168 however player able continue re-spawned dots eaten level beaten level 0 beaten player returned level 1 ghosts difficulty set high thus ghost blue time also two broken keys bottom screen one live counter one level counter disappear round beaten perfect pac-man game player achieves maximum possible score first 255 levels eating every possible dot energizer fruit enemy without losing single life using extra lives score many points possible level 256 first person credited achieving score 3,333,360 points esports player billy mitchell claimed perform feat six hours 1999 however april 2018 video game ranker twin galaxies removed mitchell scores database ruling certain donkey kong submissions achieved using original arcade hardware since mitchell pac-man achievement 7 players attained maximum score original arcade unit world record according twin galaxies currently held david race fastest completion time 3 hours 28 minutes 49 seconds maximum possible score 3,333,360 points historically december 1982 eight-year-old boy jeffrey r. yee received letter u.s. president ronald reagan congratulating worldwide record 6,131,940 points score possible passed level 256 september 1983 walter day chief scorekeeper twin galaxies took us national video game team tour east coast visit video game players said could get level 256 video game player could demonstrate ability 1999 billy mitchell offered 100,000 anyone could complete level 256 january 1 2000 prize expired unclaimed early 1970s namco primarily specialized kiddie rides japanese department stores masaya nakamura founder namco started direct company toward arcade games starting electromechanical ones f-1 1976 later hired number software engineers develop video games compete companies like atari inc. pac-man one first games developed new department within namco game developed primarily young 24-year-old employee named toru iwatani year beginning april 1979 employing nine-man team based concept eating original japanese title inspired japanese onomatopoeic phrase paku-paku describes sound mouth movement widely opened closed succession although iwatani repeatedly stated character shape inspired pizza missing slice 1986 interview admitted half-truth character design also came simplifying rounding kanji character mouth kuchi iwatani attempted appeal wider audience beyond typical demographics young boys teenagers intention attract girl gamers arcades found games played women time led add elements maze well cute ghost-like enemy characters eating gain power iwatani said concept borrowed popeye result game named puckman reference main character hockey puck shape later 1980 game picked manufacture united states bally division midway changed game name puckman pac-man effort avoid vandalism people changing letter p f spell f-word cabinet artwork also changed western markets first launched japan namco 1980 pac-man received lukewarm response space invaders similar games popular time however game success north america year took competitors distributors surprise frequently-repeated story claims marketing executives saw pac-man trade show release completely overlooked now-classic defender seeing racing game called rally-x also involves collecting items maze game outdo year pac-man quickly became popular anything seen video game industry game estimated 30 million active players across united states 1982 1983 interview nakamura said though expect pac-man successful never thought would big overtook asteroids best-selling arcade game north america grossing 1 billion quarters within year surpassing highest-grossing film time star wars arcade machines retailed around 2400 sales totaled around 1 billion equivalent billion within 18 months release 1982 400,000 arcade machines sold worldwide estimated 7 billion coins inserted combined sales counterfeit arcade machines nearly high original united states revenues pac-man licensed games products exceeded 1 billion toward end 20th century arcade game total gross consumer revenue estimated twin galaxies 10 billion quarters 2.5 billion making highest-grossing video game time beating space invaders 2016 usgamer calculated machines inflation-adjusted takings equivalent 7.68 billion pac-man awarded best commercial arcade game 1981 arcade awards ii computing listed atarisoft port tenth magazine list top apple ii games late 1985 based sales market-share data 2001 pac-man voted greatest video game time dixons poll uk game pac-man regarded one influential video games time title character first original gaming mascot game established maze chase game genre demonstrated potential characters video games increased appeal video games female audiences gaming first broad licensing success first video game power-ups individual ghosts deterministic artificial intelligence ai reacts player actions often cited first game cutscenes form brief comical interludes pac-man blinky chasing though actually space invaders part ii employed similar style between-level intermissions 1979 maze chase games exploded home computers release pac-man appeared official ports garnered attention consumers sometimes lawyers result include taxman 1981 snack attack 1982 apple ii jawbreaker 1981 atari 8-bit family scarfman 1981 trs-80 k.c munchkin 1981 odyssey² pac-man also inspired 3d variants concept monster maze 1982 spectre 1982 early first-person shooters midi maze 1987 also similar character designs john romero credited pac-man game biggest influence career wolfenstein 3d includes pac-man level first-person perspective many post- pac-man titles include power-ups briefly turn tables enemy game artificial intelligence inspired programmers later worked companies like bethesda atari inc. licensed home rights developed versions pac-man atari 2600 atari 8-bit family atari 5200 systems ports systems published atarisoft label apple ii commodore 64 vic-20 intellivision ibm pc texas instruments ti-99/4a zx spectrum one first ports march 1982 release much-maligned port atari 2600 somewhat resembles original widely criticized flickering ghosts several design implementation choices nonetheless seven million copies version pac-man sold 37.95 becoming best-selling game time console enjoying initial sales success atari overestimated demand producing 12 million cartridges 5 million went unsold richard a. edwards reviewed atari 2600 version space gamer 53 edwards commented must pac-man home 're hesitant enough differences version suggest passing port poor quality damaged company reputation among consumers retailers becoming contributing factor alongside atari e.t extra-terrestrial atari inc. decline north american video game crash 1983 namco later produced versions nintendo entertainment system game boy game boy color game gear neo geo pocket color namco ported game famicom 1985 north american operations time license atari—under tengen name—to release certain namco famicom games us audiences atari release pac-man initially licensed nintendo cartridge standard gray shell soon afterward atari began manufacturing unauthorized clones nes lockout chip produced unlicensed nes cartridges black shells including pac-man nintendo eventually discovered ruse filed lawsuit atari 1993 namco released pac-man nes three different north american releases nes pac-man —the atari gray cartridge atari black cartridge namco version—differing copyright notices title screen pac-man arcade game bonus game within super nes sega genesis pac-man world playstation pac-man party wii nintendo 3ds guinness world records awarded pac-man series eight records guinness world records gamer edition 2008 including first perfect pac-man game billy mitchell july 3 1999 score successful coin-operated game june 3 2010 nlgd festival games game creator toru iwatani officially received certificate guinness world records pac-man coin-operated arcade machines installed worldwide 293,822 record set recognized 2005 mentioned guinness world records gamer edition 2008 finally actually awarded 2010 pac-man character game series became icon video game culture 1980s wide variety pac-man merchandise marketed character image t-shirts toys hand-held video game imitations even specially shaped pasta general mills manufactured cereal pac-man name 1983 game inspired various real-life recreations involving either real people robots one event called pac-manhattan set guinness world record largest pac-man game 2004 business term pac-man defense mergers acquisitions refers hostile takeover target attempts reverse situation take would-be acquirer instead reference pac-man energizers game popularity led pac-man adopted nickname notably boxer manny pacquiao well american football player adam jones august 21 2016 2016 summer olympics closing ceremony video showcased tokyo host 2020 summer olympics small segment shows pac-man ghosts racing eating dots running track pac-man animated tv series produced hanna–barbera aired abc 1982 1983 computer-generated animated series titled pac-man ghostly adventures aired disney xd june 2013 february 2019 series also planned air universal kids ultimately canceled due low coverage nbcuniversal music buckner garcia song pac-man fever 1981 went 9 billboard hot 100 charts received gold certification 1 million records sold 1982 total 2.5 million copies sold 2008 group pac-man fever album 1982 also sold million copies 1982 weird al yankovic recorded parody taxman beatles pac-man eventually released 2017 part 1992 aphex twin name power-pill released pac-man techno album consists mostly samples game 2008 feature film based game development pac-man character appears film pixels 2015 denis akiyama playing series creator toru iwatani pac-man referenced makes appearance 2017 film guardians galaxy 2 kirito friends beat vr pac-man game called pac-man 2024 iwatani makes cameo beginning film arcade technician japanese tokusatsu film kamen rider heisei generations dr. pac-man vs. ex-aid ghost legend riders pac-man-like character introduced main villain 2019 film relaxer uses pac-man strong plot element form 1999 couch-bound man attempts beat game encounters famous level 256 glitch y2k occurs 1982 milton bradley released board game based pac-man players move four pac-man characters traditional yellow plus red green blue plus two ghosts per throws pair dice sticker manufacturer fleer included rub-off game cards pac-man stickers card packages contain pac-man style maze points along path hidden opaque coverings starting position player moves around maze scratching coverings score points pac-man playable character super smash bros. nintendo 3ds wii u 3ds version stage based original arcade game called pac-maze pac-man amiibo figurine also released nintendo may 29 2015 pac-man later returned playable character super smash bros ultimate within mathematical research field dynamical systems new kind renormalization called pac-man renormalization introduced dzmitry dudko mikhail lyubich nikita selinger name inspired visual similarity pac-man figure main object study theory announced 2017 advanced 2018 made significant advances study famous mandelbrot set pac-man one games consistently published three decades remade numerous platforms spawning many sequels pac-man included namco long-running namco museum compilations well microsoft return arcade downloads game made available game services xbox live arcade gametap virtual console namco released mobile versions pac-man brew java ios well palm pdas windows mobile-based devices pac-man numerous sequels spin-offs one designed original designer toru iwatani follow-ups developed namco either including significant midway ms. pac-man released united states 1981 originally called crazy otto unauthorized hack pac-man created general computer corporation sold midway without namco permission bally-midway released several unauthorized spin-offs pac-man plus jr. pac-man baby pac-man professor pac-man resulting namco severing business relations midway coleco tabletop mini-arcade versions game yielded 1.5 million units sold 1982 nelsonic industries produced pac-man lcd wristwatch game simplified maze also 1982 namco repeatedly re-released game arcades 2001 namco released ms. pac-man galaga class 1981 reunion edition cabinet pac-man available play hidden game commemorate pac-man 25th anniversary 2005 namco released revision officially featured three games june 5 2007 first pac-man world championship held new york city brought together ten competitors eight countries play new pac-man championship edition developed toru iwatani sequel released november 2010 namco networks sold downloadable windows pc version pac-man 2009 also includes enhanced mode replaces original sprites sprites pac-man championship edition namco networks made downloadable bundle includes pc version pac-man port dig dug called 2010 namco bandai announced release game windows phone 7 xbox live game weekend may 21–23 2010 google changed logo homepage playable version game recognition 30th anniversary game release google doodle version pac-man estimated played 1 billion people worldwide 2010 google later allowed access game separate web page april 2011 soap creative published world biggest pac-man working together microsoft namco-bandai celebrate pac-man 30th anniversary multiplayer browser-based game user-created interlocking mazes 2016 in-app version pac-man introduced facebook messenger allows users play game friends talking facebook
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Computer architecture
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passband passband range frequencies wavelengths pass filter example radio receiver contains bandpass filter select frequency desired radio signal radio waves picked antenna passband receiver range frequencies receive bandpass-filtered signal signal energy passband known bandpass signal contrast baseband signal telecommunications optics acoustics passband band-pass filtered signal portion frequency spectrum transmitted minimum relative loss maximum relative gain filtering device words band frequencies pass es filter set filters accompanying figure shows schematic waveform filtered bandpass filter consisting highpass lowpass filter radio receivers generally include tunable band-pass filter passband wide enough accommodate bandwidth radio signal transmitted single station two main categories digital communication transmission methods baseband passband general inverse relationship width filter passband time required filter respond new inputs broad passbands yield faster response times consequence mathematics fourier analysis limiting frequencies passband defined relative intensity power decreases specified fraction maximum intensity power decrease power often specified half-power points i.e 3 db maximum power difference limiting frequencies called bandwidth expressed hertz optical regime nanometers micrometers differential wavelength related term bandpass adjective describes type filter filtering process frequently confused passband refers actual portion affected spectrum two words compound words follow english rules formation primary meaning latter part compound modifier first part hence one may correctly say dual bandpass filter two passbands
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Internet protocols
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password length parameter telecommunication password length parameter basic parameter value affects password strength brute force attack contributor computer security one use password length parameters expression formula_1 formula_2 probability password guessed lifetime formula_3 maximum lifetime password used log system formula_4 number guesses per unit time formula_5 number unique algorithm-generated passwords 'password space degree password security determined probability password guessed lifetime
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Computer security
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ontap ontap data ontap clustered data ontap cdot data ontap 7-mode netapp proprietary operating system used storage disk arrays netapp fas aff ontap select cloud volumes ontap release version 9.0 netapp decided simplify data ontap name removed word data remove 7-mode image therefore ontap 9 successor clustered data ontap 8 ontap includes code berkeley net/2 bsd unix spinnaker networks technology operating systems ontap originally supported nfs later added support smb iscsi fibre channel protocol including fibre channel ethernet fc-nvme june 16 2006 netapp released two variants data ontap namely data ontap 7g nearly complete rewrite data ontap gx data ontap gx based grid technology acquired spinnaker networks 2010 software product lines merged one os data ontap 8 folded data ontap 7g onto data ontap gx cluster platform data ontap 8 includes two distinct operating modes held single firmware image modes called ontap 7-mode ontap cluster-mode last supported version ontap 7-mode issued netapp version 8.2.5 subsequent versions ontap version 8.3 onwards one operating mode ontap cluster-mode majority large-storage arrays vendors tend use commodity hardware operating system microsoft windows server vxworks tuned linux netapp storage arrays use highly customized hardware proprietary ontap operating system originally designed netapp founders david hitz james lau specifically storage-serving purposes ontap netapp internal operating system specially optimized storage functions high low level original version ontap proprietary non-unix kernel tcp/ip stack networking commands low-level startup code bsd version descended data ontap gx boots freebsd stand-alone kernel-space module uses functions freebsd example uses command interpreter drivers stack ontap also used virtual storage appliances vsa ontap select cloud volumes ontap based previous product named data ontap edge storage array hardware include battery-backed non-volatile memory allows commit writes stable storage quickly without waiting disks virtual storage appliances using virtual nonvolatile memory implementers often organize two storage systems high-availability cluster private high-speed link either fibre channel infiniband 10 gigabit ethernet 40 gigabit ethernet 100 gigabit ethernet one additionally group clusters single namespace running cluster mode data ontap 8 operating system ontap 9 data ontap made available commodity computing servers x86 processors running atop vmware vsphere hypervisor name ontap edge later ontap edge renamed ontap select kvm added supported hypervisor data ontap including wafl developed 1992 david hitz james lau michael malcolm initially supported nfsv2 cifs protocol introduced data ontap 4.0 1996 april 2019 octavian tanase svp ontap posted preview photo twitter ontap running kubernetes container demonstration write anywhere file layout wafl file layout used ontap os supports large high-performance raid arrays quick restarts without lengthy consistency checks event crash power failure growing size filesystems quickly ontap os contains number storage efficiencies based wafl functionalities supported protocols require licenses february 2018 netapp claims aff systems clients gain average 4.72:1 storage efficiency deduplication compression compaction clones savings starting ontap 9.3 offline deduplication compression scanners start automatically default based percentage new data written instead scheduling br cross-volume deduplication storage efficiency features work ssd media inline offline deduplication mechanisms leverage databases consist links data blocks checksums data blocks handled deduplication process deduplication database located volume aggregates deduplication enabled flash fas systems support post-process compression order storage efficiencies execution follows one multiple raid groups form aggregate within aggregates ontap operating system sets flexible volumes flexvol actually store data users access similarly raid-0 aggregate consolidates space underlying protected raid groups provide one logical piece storage flexible volumes alongside aggregates consists netapp disks raid groups aggregates could consist luns already protected third-party storage systems flexarray ontap select cloud volumes ontap aggregate could consist either luns netapp raid groups alternative traditional volumes one raid groups form single static volume flexible volumes offer advantage many created single aggregate resized time smaller volumes share spindles available underlying aggregate combination storage qos allows change performance flexible volumes fly traditional volumes n't however traditional volumes theoretically handle slightly higher i/o throughput flexible volumes number spindles go additional virtualization layer talk underlying disk aggregates traditional volumes expanded never contracted current maximum aggregate physical useful space size 800 tib all-flash fas systems first form redundancy added ontap ability organize pairs netapp storage systems high-availability cluster ha-pair ha-pair could scale capacity adding disk shelves performance maximum reached ha-pair two ways proceed one buy another storage system divide workload another buy new powerful storage system migrate workload aff fas storage systems usually able connect old disk shelves previous models—this process called head-swap head-swap requires downtime re-cabling operations provides access old data new controller without system re-configuration data ontap 8 firmware image contains two operating systems named modes 7-mode cluster-mode modes could used fas platform one time however data modes n't compatible case fas conversion one mode another case re-cabling disk shelves 7-mode cluster-mode vice versa later netapp released 7-mode transition tool 7mtt able convert data old disk shelves 7-mode cluster-mode named copy-free transition process required downtime version 8.3 7-mode removed data ontap firmware image clustered ontap new advanced os compared predecessor data ontap version 7 version 8 7-mode able scale adding new ha-pairs single namespace cluster transparent data migration across entire cluster version 8.0 new aggregate type introduced size threshold larger 16-terabyte tb aggregate size threshold supported previous releases data ontap also named 64-bit aggregate version 9.0 nearly features 7-mode successfully implemented ontap clustered including snaplock many new features available 7-mode introduced including features flexgroup fabricpool new capabilities fast-provisioning workloads flash optimization uniqueness netapp clustered ontap ability add heterogeneous systems systems single cluster model generation single cluster provides single pane glass managing nodes cluster non-disruptive operations adding new models cluster removing old nodes online migration volumes luns data contiguously available clients version 9.0 netapp renamed data ontap ontap ontap considered unified storage system meaning supports block-level fc fcoe nvmeof iscsi file-level nfs pnfs cifs/smb protocols clients sds versions ontap ontap select cloud volumes ontap support fc fcoe nvmeof protocols due software-defined nature nfs first protocol available ontap latest versions ontap 9 support nfsv2 nfsv3 nfsv4 4.0 4.1 pnfs starting ontap 9.5 4-byte utf-8 sequences characters outside basic multilingual plane supported names files directories ontap supports cifs 2.0 higher smb 3.1 starting ontap 9.4 smb multichannel provides functionality similar multipathing san protocols supported starting ontap 8.2 cifs protocol supports continuous availability ca smb 3.0 microsoft hyper-v smb sql server smb ontap supports smb encryption also known sealing accelerated aes instructions intel aes ni encryption supported smb 3.0 later ontap physical appliances supports fcoe well fc protocol depending hba port speed iscsi data center bridging dcb protocol supported a220/fas2700 systems nvme fabrics nvmeof refers ability utilize nvme protocol existed network infrastructure like ethernet converged traditional tcp fiber channel infiniband transport opposite run nvme pci nvme san block level data storage protocol nvmeof supported all-flash a-systems supported low-end a200 a220 systems starting ontap 9.5 ana protocol supported provide similarly alua multi-pathing functionality nvme ana nvme currently supported suse enterprise linux 15 fc-nvme without ana supported suse enterprise linux 12 sp3 redhat enterprise linux 7.6 starting ontap 9.4 netapp supports nvmeof fiber channel protocol 32/16 gb fc-nvme all-flash fas systems a800 a700/a700s a300 supported os fc-nvme oracle linux vmware windows server suse linux redhat linux high availability ha clustered configuration storage system two nodes ha pairs aims ensure agreed level operational expected unexpected events like reboots software firmware updates even though single ha pair consists two nodes controllers netapp designed way behaves single storage system ha configurations ontap employ number techniques present two nodes pair single system allows storage system provide clients nearly-uninterruptable access data node either fail unexpectedly need rebooted operation known takeover example network level ontap temporarily migrate ip address downed node surviving node applicable also temporarily switch ownership fc wwpns downed node surviving node data level contents disks assigned downed node automatically available use via surviving node fas aff storage systems use enterprise level hdd ssd drives housed within disk shelves two bus ports one port connected controller ontap disks ownership marker written reflect controller ha pair owns serves individual disk aggregate include disks owned single node therefore aggregate owned node upper objects flexvol volumes luns file shares served single controller controller disks aggregates serve therefore ha pair configurations called active/active nodes utilized simultaneously even though serving data downed node ha pair repaired whatever maintenance window necessitated takeover completed downed node running without issue giveback command issued bring ha pair back active/active status high-availability clusters ha clusters first type clusterization introduced ontap systems aimed ensure agreed level operation often confused horizontal scaling ontap clusterization came spinnaker acquisition therefore netapp documentation refers ha configuration ha pair rather ha cluster ha pair uses form network connectivity often direct connectivity communication servers pair called ha interconnect ha-ic ha interconnect use ethernet infiniband communication medium ha interconnect used non-volatile memory log nvlog replication using rdma technology purposes ensure agreed level operational events like reboots always two nodes ha pair configuration ontap assigns dedicated non-sharable ha ports ha interconnect could external build chassis visible outside ha-ic confused intercluster intracluster interconnect used snapmirror coexist data protocols data ports cluster interconnect ports used horizontal scaling online data migration across multi-node cluster ha-ic interfaces visible node shell level starting a320 ha-ic cluster interconnect traffic start use ports metrocluster mc additional level data availability ha configurations supported fas aff storage systems later sds version metrocluster introduced ontap select cloud volumes ontap products mc configuration two storage systems system single node ha pair form metrocluster often two systems located two sites distance 300 km therefor called geo-distributed system plex key underlying technology synchronizes data two sites metrocluster mc configurations nvlog also replicated storage systems sites uses dedicated ports purpose addition ha interconnect starting ontap 9.5 svm-dr supported metrocluster configurations feature ontap select software similarly metrocluster fas/aff systems metrocluster sds mc sds allows synchronously replicate data two sites using syncmirror automatically switch survived node transparently users applications metrocluster sds work ordinary ha pare data volumes luns lifs could moved online aggregates controllers sites slightly different traditional metrocluster fas/aff systems data cloud moved across storage cluster within site data originally located traditional metrocluster way applications access data locally remote site disable one entire site process called switchover mc sds ordinary ha process occurs metrocluster sds uses ontap deploy mediator fas aff world functionality known metrocluster tiebreaker came ontap select bundle generally used deploying clusters installing licenses monitoring horizontal scaling ontap clusterization came spinnaker acquisitions often referred netapp single namespace horizontal scaling cluster ontap storage system cluster ontap cluster therefore often confused ha pair even metrocluster functionality metrocluster ha data protection technologies single namespace clusterization provide data protection ontap cluster formed one ha pairs adds ontap system non-disruptive operations ndo functionality non-disruptive online data migration across nodes cluster non-disruptive hardware upgrade data migration ndo operations ontap cluster require dedicated ethernet ports operations called cluster interconnect use ha interconnect purposes cluster interconnect ha interconnect could share ports cluster interconnect single ha pair could directly connected cluster interconnect ports systems 4 nodes require two dedicated ethernet cluster interconnect switches ontap cluster could consist even number nodes must configured ha pairs except single-node cluster single-node cluster ontap system also called non-ha stand-alone ontap cluster managed single pain glass built-in management web-based gui cli ssh powershell api ontap cluster provides single name space ndo operations svm single namespace ontap system name collection techniques used cluster separate data front-end network connectivity data protocols like fc fcoe fc-nvme iscsi nfs cifs therefore provide kind data virtualization online data mobility across cluster nodes network layer single namespace provide number techniques non-disruptive ip address migration like cifs continuous availability transparent failover netapp network failover nfs san alua path election online front-end traffic re-balancing data protocols netapp aff fas storage systems consists different ha pairs aff fas different models generations include 24 nodes nas protocols 12 nodes san protocols sds systems ca n't intermix physical aff fas storage systems also known vserver sometimes svm storage virtual machine svm layer abstraction alongside functions responsible virtualizing separate physical front-end data network data located flexvol volumes used non-disruptive operations multi-tenancy non disruptive operations ndo operations clustered ontap system ndo data operations include aggregate relocation within ha pair nodes flexvol volume online migration known volume move operation across aggregates nodes within cluster luns migration known lun move operation flexvol volumes within cluster lun move volume move operations use cluster interconnect ports data transfer ha-ci use operations svm behave differently network ndo operations depending front-end data protocol decrease latency original level flexvol volumes luns located node network address clients access storage system network address could created san moved nas protocols ndo operations free functionality nas front-end data protocols nfsv2 nfsv3 nfsv4 cifsv1 smbv2 smb v3 provide network redundancy protocol rely storage switch functionalities matter reason ontap support ethernet port channel lacp ethernet network ports l2 layer known ontap interface group ifgrp within single node also non-disruptive network fail nodes cluster l3 layer migrating logical interfaces lif associated ip addresses similar vrrp survived node back home failed node restored front-end data san protocols alua feature used network load balancing redundancy san protocols ports node data located reported clients active preferred path load balancing network ports nodes cluster active non-preferred path case one port entire node goes client access data using non-preferred path starting ontap 8.3 selective lun mapping slm introduced reduce number paths lun removes non-optimized paths lun cluster nodes except ha partner node owning lun cluster report host paths ha pare lun located ontap provides alua functionality san protocols san network lifs migrate like nas protocols data network interfaces migration finished transparent storage system clients due ontap architecture cause temporary permanent data indirect access ontap cluster interconnect ha-ci use situations slightly increase latency clients san lifs used fc fcoe iscsi fc-nvme protocols vip virtual ip lifs require top-of-the-rack bgp router used bgp data lifs alongside nas lifs also used ethernet nas environment case bgp lifs automatically load-balance traffic based routing metrics avoid inactive unused links bgp lifs provide distribution across nas lifs cluster limited single node nas lifs bgp lifs provide smarter load balancing realized hash algorithms ethernet port channel lacp interface groups vip lif interfaces tested used mcc svm-dr. node management lif interface migrate associated ip address across ethernet ports single node available ontap running node usually located e0m port node node management ip sometimes used cluster admin communicate node cluster shell rare cases commands issued particular node cluster managment lif interface associated ip address available entire cluster running default migrate across ethernet ports often located one e0m ports one cluster nodes used cluster administrator management purposes used api communications html gui ssh console management default ssh connect administrator cluster shell service processor sp interfaces available hardware appliances like fas aff allows ssh out-of-band console communications embedded small computer installed controller mainboard similarly ipmi allows connect monitor manage controller even ontap os booted sp possible forcibly reboot halt controller monitor coolers temperature etc connection sp ssh brings administrator sp console connected sp possible switch cluster shell controller one sp migrate like management interfaces usually e0m sp lives single management wrench physical ethernet port dedicated mac address node lifs cluster lif sp often using ip subnet svm management lif similarly cluster management lif migrate across ethernet ports nodes cluster dedicated single svm management svm lif gui capability facilitate api communications ssh console management svm management lif live e0m port often located data port cluster node dedicated management vlan different ip subnets node cluster lifs cluster interconnect lif interfaces using dedicated ethernet ports share ports management data interfaces horizontal scaling functionality times like lun volume migrates one node cluster another cluster interconnect lif similarly node management lifs migrate ports single node intercluster interface lifs live share ethernet ports data lifs used snapmirror replication intercluster interface lifs similarly node management lifs cluster interconnect migrate ports single node ontap provide two techniques multi tenancy functionality like storage virtual machines ip spaces one hand svms similar virtual machines like kvm provide visualization abstraction physical storage another hand quite different unlike ordinary virtual machines svms allow run third party binary code like pure storage systems provide virtualized environment storage resources instead also svms unlike ordinary virtual machines run single node end user looks like svm runs single entity node whole cluster svm divides storage system slices divisions even organizations share storage system without knowing interfering utilizing ports data aggregates nodes cluster using separate flexvol volumes luns svm run frontend data protocols set users use network addresses management ip use ip spaces users ip addresses networks storage system without interfering ontap system must run least one data svm order function may run levels ontap management cluster admin level available privileges data svm provides owner vsadmin nearly full functionality cluster admin level lacks physical level management capabilities like raid group configuration aggregate configuration physical network port configuration however vsadmin manage logical objects inside svm like create delete configure luns flexvol volumes network addresses two svms cluster ca n't interfere one svm create delete modify even see objects another svm svm owners environment looks like users entire storage system cluster multi tenancy free functionality ontap flexclone licensed feature used creating writable copies volumes files luns case volumes flexclone acts snapshot allows write ordinary snapshot allows read data wafl architecture flexclone technology copies metadata inodes provides nearly instantaneous data copying file lun volume regardless size snaprestore licensed feature used reverting active file system flexvol previously created snapshot flexvol restoring metadata inodes active file system snaprestore used also single file restore lun restore previously created snapshot flexvol object located without snaprestore license nas environment possible see snapshots network file share able copy directories files restore purposes san environment way restore operations similar nas environment possible copy san nas environments files directories luns entire flexvol content ontap command ndmpcopy free process copying data depend size object could time consuming snaprestore mechanism restoring metadata inodes active file system almost instant regardless size object restored previous state flexgroup free feature introduced version 9 utilizes clustered architecture ontap operating system flexgroup provides cluster-wide scalable nas access nfs cifs protocols flexgroup volume collection constituent flexvol volumes distributed across nodes cluster called constituents transparently aggregated single space therefore flexgroup volume aggregates performance capacity constituents thus nodes cluster located end user flexgroup volume represented single ordinary file-share full potential flexgroup revealed technologies like pnfs currently supported flexgroup nfs multipathing session trunking also available ontap smb multichannel currently supported flexgroup smb continuous availability flexgroup smb ca supported ontap 9.6 vip bgp flexgroup feature ontap 9 allows massively scale single namespace 20pb 400 billion files evenly spreading performance across cluster starting ontap 9.5 fabricpool supported flexgroup recommended constituent volumes backup single s3 bucket supports smb features native file auditing fpolicy storage level access guard sla copy offload odx inherited watches changes notifications quotas qtree smb contiguous availability ca supported flexgroup allows running ms sql hyper-v flexgroup flexgroup supported metrocluster snapshots form basis netapp asynchronous disk-to-disk replication d2d technology snapmirror effectively replicates flexible volume snapshots two ontap systems snapmirror also supported ontap cloud backup solidfire ontap systems part netapp data fabric vision netapp also offers d2d backup archive feature named snapvault based replicating storing snapshots open systems snapvault allows windows unix hosts back data ontap store filesystem changes snapshots supported ontap 8.3 onwards snapmirror designed part disaster recovery plan stores exact copy data time snapshot created disaster recovery site could keep snapshots systems snapvault hand designed store less snapshots source storage system snapshots secondary site long period time br data captured snapvault snapshots destination system could modified accessible destination read-write data restored back primary storage system snapvault snapshot could deleted data captured snapshots sites snapmirror snapvault cloned modified flexclone feature data cataloging backup consistency validation test development purposes etc br later versions ontap introduced cascading replication one volume could replicate another another configuration called fan-out deployment one volume replicated multiple storage systems fan-out cascade replication deployments support combination snapmirror dr snapvault unified replication possible use fan-in deployment create data protection relationships multiple primary systems single secondary system relationship must use different volume secondary system starting ontap 9.4 destination snapmirror snapvault systems enable automatic inline offline deduplication default br intercluster relationship two clusters snapmirror intracluster opposite used snapmirror relationship storage virtual machines svm single cluster br snapmirror operate version-dependent mode two storage systems must run version ontap version-flexible mode types snapmirror replication br snapmirror-based technologies br snapmirror licensed feature snapvault license required snapmirror license already installed svm dr based snapmirror technology transferring volumes exceptions allowed data protected svm dr site two modes svm dr identity preserve identity discard identity discard mode one hand data volumes copied secondary system dr svm preserve information like svm configuration ip addresses cifs ad integration original svm another hand identity discard mode data secondary system brought online read-write mode primary system online might helpful dr testing test/dev purposes therefore identity discard requires additional configuration secondary site case disaster occurs primary site identity preserve mode svm-dr copying volumes data also information like svm configuration ip addresses cifs ad integration requires less configuration dr site case disaster event primary site mode primary system must offline ensure conflict snapmirror sync sm-s short zero rpo data replication technology previously available 7-mode systems available clustered ontap version 9.5 snapmirror sync replicates data volume level requirements rtt less 10ms gives distance approximately 150 km snapmirror sync work two modes full synchronous mode set default guarantees zero application data loss two sites disallowing writes snapmirror sync replication fails reason relaxed synchronous mode allows application write continue primary site snapmirror sync fails relationship resumed automatic re-sync occur sm-s supports fc iscsi nfsv3 nfsv4 smb v2 smb v3 protocols limit 100 volumes aff 40 volumes fas 20 ontap select work controllers 16gb memory sm-s useful replicating transactional logs oracle db ms sql ms exchange etc source destination flexvolumes fabricpool aggregate must use backup policy flexgroup volumes quotas currently supported sm-s. sm-s free feature license included premium bundle unlike syncmirror sm-s uses raid plex technologies therefore configured two different netapp ontap storage systems different disk type media flexcache technology previously available 7-mode systems available clustered ontap version 9.5 flexcache allows serving nas data across multiple global sites file locking mechanisms flexcache volumes cache reads writes metadata writes edge generating push operation modified data edge ontap systems requested data origin 7-mode writes go origin edge ontap system job check file n't updated also flexcache volumes less size original volume also improvement compare 7-mode initially nfs v3 supported ontap 9.5 flexcache volumes sparsely-populated within ontap cluster intracluster across multiple ontap clusters inter-cluster flexcache communicates intercluster interface lifs nodes licenses flexcache based total cluster cache capacity included premium bundle fas aff ontap select combined use flexcache technology allowed create 10 flexcache volumes per origin flexvol volume 10 flexcache volumes per ontap node original volume must stored flexvol wile flexcache volumes flexgroup volume format data ontap also implements option named raid syncmirror rsm using plex technique raid groups within aggregate traditional volume synchronously duplicated another set hard disks typically done another site via fibre channel ip link within single controller local syncmirror single disk-shelf resiliency netapp metrocluster configuration uses syncmirror provide geo-cluster active/active cluster two sites 300 km apart 700 km ontap 9.5 mcc-ip syncmirror used either software-defined storage platforms cloud volumes ontap ontap select provides high availability environments directly attached non-shared disks top commodity servers fas aff platforms local syncmirror metrocluster configurations syncmirror free feature snaplock implements write read many worm functionality magnetic ssd disks instead optical media data deleted retention period reached snaplock exists two modes compliance enterprise compliance mode designed assist organizations implementing comprehensive archival solution meets strict regulatory retention requirements regulations dictated sec 17a-4 f rule finra hipaa cftc rule 1.31 b dach sarbanes-oxley gdpr check 21 eu data protection directive 95/46/ec nf z 42-013/nf z 42-020 basel iii mifid patriot act graham-leach-bliley act etc records files committed worm storage snaplock compliance volume altered deleted expiration retention period moreover snaplock compliance volume destroyed data reached end retention period snaplock licensed feature snaplock enterprise geared toward assisting organizations self-regulated want flexibility protecting digital assets worm-type data storage data stored worm snaplock enterprise volume protected alteration modification one main difference snaplock compliance files stored strict regulatory compliance snaplock enterprise volume destroyed administrator root privileges ontap system containing snaplock enterprise volume even designed retention period yet passed modes retention period extended shortened incongruous concept immutability also netapp snaplock data volumes equipped tamper-proof compliance clock used time reference block forbidden operations files even system time tampered starting ontap 9.5 snaplock supports unified snapmirror xdp engine re-synchronization fail-over without data loss 1023 snapshots efficiency mechanisms clock synchronization sds ontap available ssd-only aggregates fas/aff systems cloud volumes ontap ssd media starting ontap 9.4 fabricpool supported ontap select platform cloud volumes ontap also supports hdd s3 fabricpool configuration fabric pool provides automatic storage tiering capability cold data blocks fast media usually ssd ontap storage cold media via object protocol object storage s3 back fabric pool configured two modes one mode used migrate cold data blocks captured snapshots mode used migrate cold data blocks active file system fabricpool preserves offline deduplication offline compression savings starting ontap 9.4 introduced fabricpool 2.0 ability tier-off active file system data default 31-day data accessed support data compaction savings recommended ratio 1:10 inodes data files clients connected ontap storage system fabric pool data-tiering operations completely transparent case data blocks become hot copied back fast media ontap storage system fabric pool currently compatible netapp storagegrid amazon s3 google cloud alibaba object storage services starting ontap 9.4 azure blob supported starting 9.5 ibm cloud object storage icos amazon commercial cloud services c2s supported object-based sw services could used requested user service validated netapp flexgroup volumes supported fabricpool starting ontap 9.5 fabric pool feature fas/aff systems free use netapp storagegrid external object storage object storage systems amazon s3 azure blob fabric pool must licensed per tb function alongside costs fabric pool licensing customer needs also pay consumed object space cloud volumes ontap storage system fabric pool require licensing costs apply consumed space object storage starting ontap 9.5 capacity utilization triggering tiering hot tier adjusted svm-dr also supported flexgroups netapp storage systems running ontap flash cache formally performance accelerate module pam custom purpose-built proprietary pcie card hybrid netapp fas systems flash cache reduce read latencies allows storage systems process read-intensive work without adding spinning disk underlying raid since read operations require redundancy case flash cache failure flash cache works controller level accelerates read operations separate volume controller different caching policy read cache could disabled volume flashcache caching policies applied flexvol level flashcache technology compatible flexarray feature starting 9.1 single flexvol volume benefit flashpool flashcache caches simultaneously starting ontap 9.5 flash cache read-cache technology available cloud volumes ontap use ephemeral ssd drives ndas proxy service introduced ontap 9.5 works conjunction ndas service cloud provider similarly fabricpool ndas stores data object format unlike fabricpool stores wafl metadata object storage well information transferred ontap system snapshot deltas entire set data already deduplicated compressed volume level ndas proxy basically http s3 object protocol additional api calls cloud ndas ontap 9.5 works schema primary ontap 9 storage replicating data via snapmirror secondary ontap 9.5 storage secondary storage also ndas proxy storage qos free feature ontap systems types storage qos ontap systems adaptive qos a-qos includes absolute minimum qos ordinary static qos minimum qos qos min maximum qos qos max maximum qos configured static upper limit iops mb/s applied object volume lun file prevent object consuming storage performance resources defined administrator thus isolating performance-intensive bullies protecting workloads minimum qos contrary maximum set volumes ensure volume get less configured administrator static number iops contention storage performance resources could applied volumes a-qos mechanism automatically changing qos based consumed space flexible volume consumed space could grow decrease size flexvol changed fas systems a-qos reconfigures peak performance qos max aff systems reconfigure expected performance qos min peak performance qos max volume a-qos allows ontap automatically adjust number iops volume based a-qos policies three basic a-qos policies extreme performance value a-qos policy predefined fixed ratio io per tb peak performance expected performance absolute minimum qos absolute minimum qos used instead expected performance qos min volume size ratio io per tb small example 10gb ontap os number features increase security storage system like onboard key manager passphrase controller boot nse nve encryption usb key manager available starting 9.4 auditing nas events another security measure ontap enables customer track log certain cifs nfs events storage system helps track potential security problems provides evidence security breaches ontap accessed ssh ability authenticate common access card ontap supports rbac role-based access control allows administrative accounts restricted and/or limited actions take system rbac prevents single account allowed perform potential actions available system beginning ontap 9 kerberos 5 authentication privacy service krb5p supported nas krbp5 authentication mode protects data tampering snooping using checksums encrypt traffic client server ontap solution supports 128-bit 256-bit aes encryption kerberos onboard key manager free feature introduced 9.1 store keys nve encrypted volumes nse disks nse disks available aff/fas platforms ontap systems also allow storing encryption keys usb drive connected appliance ontap also use external key manager like gemalto trusted key manager netapp volume encryption nve flexvol volume-level software-based encryption uses storage cpu data encryption purposes thus performance degradation expected though less noticeable high-end storage systems cpu cores nve licensed free feature compatible nearly netapp ontap features protocols similarly netapp storage encryption nse nve store encryption key locally dedicated key manager like ibm security key lifecycle manager safenet keysecure cloud key managers nve like nse also data rest encryption means protects physical disks theft give additional level data security protection normal operational running system nve combination fabricpool technology also protect data unauthorized access external s3 storage systems like amazon since data already encrypted transferring wire encrypted form starting ontap 9.4 new feature introduced called secure purge provides ability securely delete file comply gdpr requirements ontap vscan fpolicy aimed malware prevention ontap systems nas vscan provides way netapp antivirus scanner partners verify files virus free fpolicy integrates netapp partners monitor file access behaviors fpolicy file-access notification system monitor activity nas storage prevent unwanted access change files based policy settings helps prevent ransomware getting foothold first place mtu black-hole detection path mtu discovery pmtud processes ontap system connected via ethernet network detects maximum mtu size ontap 9.2 online certificate status protocol ocsp ldap tls iscsi endpoint isolation specify range ip addresses log storage limit number failed login attempts ssh ntp symmetric authentication supported starting ontap 9.5 netapp offers set server-based software solutions monitoring integration ontap systems commonly-used free software oncommand unified performance manager data availability performance monitoring solution netapp workflow automation wfa free server-based product used netapp storage orchestration includes self-service portal web-based gui nearly routine storage operations sequences operations configured workflows published service end users order consume netapp storage service snapcenter previously known snapmanager suite server-based product netapp also offers products taking application-consistent snapshots coordinating application netapp storage array products support microsoft exchange microsoft sql server microsoft sharepoint oracle sap vmware esx server data products form part snapmanager suite snapcenter also includes third-party plugins mongodb ibm db2 mysql allows end user create plugins integration ontap storage system snapmanager snapcenter enterprise-level licensed products similar free less capable netapp product exists named snapcreator intended customers wish integrate ontap application-consistent snapshots applications license snapcenter netapp claims snapcenter capabilities expand include solidfire storage endpoints snapcenter controller based licensing aff/fas systems terabyte sds ontap snapcenter plug-in gor vmware vsphere called netapp data broker separate linux-based applience used without snapcenter netapp services level manager nslm short software provisioning ontap storage delivers predictable performance capacity data protection workload exposes restful apis built-in swagger documentation list available apis also integrated netapp storage products like oncommand unified manager nslm exposes three standard service levels ssl based service level objectives slo creates custom service levels nslm created provide predicted serviceprovider-like storage consumption nslm space-based licensed product ontap systems ability integrate hadoop teragen teravalidate terasort apache hive apache mapreduce tez execution engine apache spark apache hbase azure hdinsight hortonworks data platform products cloudera cdh netapp in-place analytics module also known netapp nfs connector hadoop provide access analyze data using external shared nas storage primary secondary hadoop storage ontap provisioning usage automated many ways directly use additional netapp software 3rd party software ontap operating system used storage disk arrays three platforms ontap software used netapp fas aff ontap select cloud volumes ontap platform ontap uses kernel slightly different set features fas richest functionality among platforms fas flash fas aff systems proprietary custom-built hardware netapp ontap software aff systems contain ssd drives ontap aff optimized tuned flash memory fas systems may contain hdd hdd-only systems hdd ssd hybrid systems ontap fas aff platforms create raid arrays raid-4 raid-dp raid-tec arrays disks disk partitions data protection reasons ontap select cloud volumes ontap leverage raid data protection provided environment run fas aff systems support metro cluster functionality ontap select cloud volumes ontap platforms ontap select cloud volumes ontap virtual storage appliances vsa based previous product ontap edge also known ontap-v considered software-defined storage ontap select cloud volumes ontap includes plex aggregate abstractions n't lower level raid module included os therefore raid-4 raid-dp raid-tec supported ontap storage system similarly flexarray functionality leverages raid data protection ssd hdd drive level underlying storage systems starting ontap select 9.4 ontap deploy 2.8 software raid supported requirements 3rd party hw raid equipment ontap select cloud volumes ontap virtual machines n't support fibre channel fibre channel ethernet front-end data protocols consume space underlying storage hypervisor added vsa virtual disks represented treated inside ontap disks ontap select cloud volumes ontap provide high availability deduplication resiliency data recovery robust snapshots integrated application backup application consistent snapshots nearly ontap functionality exceptions software-defined versions ontap nearly functionality except hardware-centric features like ifgroups service processor physical disk drives encryption metrocluster fcp fiber channel protocol ontap select run vmware esxi linux kvm hypervisors ontap select leveraged raid data protection ssd hdd drive level underlying das san vsan storage systems starting ontap select 9.4 ontap deploy 2.8 software raid supported requirements 3rd party hw raid equipment kvm staring ontap 9.5 esxi ontap deploy virtual machine provides mediator function metrocluster 2-node configurations keeps track licensing used initial cluster deployment starting ontap deploy 2.11.2 vcenter plugin introduced allows performing ontap deploy functionality vcenter previously management performed either command line vsphere vm ova setup master like fas platform ontap select supports high availability clustering fas platform ontap select offered two versions hdd-only flash optimized previously ontap select known data ontap edge data ontap edge product data ontap os version 8 able run atop vmware esxi starting ontap 9.5 sw-metrocluster nsx overlay network supported starting ontap 9.5 licensing changed capacity tier-based licenses linked node perpetual capacity pool licensing time-limited subscription ontap select 9.5 get mqtt protocol supported data transferring edge data center cloud april 2019 octavian tanase svp ontap posted preview photo twitter ontap running kubernetes container demonstration cloud volumes ontap formally ontap cloud includes nearly functionality ontap select also virtual storage appliance vsa ordered hyper-scale providers cloud computing amazon aws microsoft azure ibm cloud uses ontap select reasons instead cloud volumes ontap cloud volumes ontap provide high availability data across different regions cloud cloud volumes ontap leverages raid data protection ssd hdd drive level underlying ip san storage system cloud provider feature comparison platforms latest ontap version
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Operating systems
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rockchip rk3288 rockchip rk3288 arm architecture system chip soc rockchip first soc august 2014 uses 32 bit arm cortex-a17 processor quad-core processor neon coprocessor hardware acceleration video 3d graphics used number chromebooks low-power low-performance devices rk3288-c used veyron board design several chromebooks powers following devices
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Computer architecture
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ip reader ip reader electronic security device designed identify users control entry exit protected areas ip reader two features distinguish access control readers first ip reader introduced 1999 isonas security systems inc hid global one major manufacturers access control reader card business followed move network-based security systems 8 years later introduction edge ip reader family 2007 biometric reader manufacturers sagem securite suprema inc. also added ip readers product line-up ip readers potential make significant impact security market open communication standards existed currently access control systems utilize proprietary communication protocols effectively eliminate freedom choice decision install certain access control system made end-user locked buying brand readers controllers cards software receiving service dealer exclusive rights represent particular brand area hardware software different manufacturers compatible open communication standards supported access control manufacturers ip reader market segment could enjoy growth similar ip cameras standard hardware platform would increase interoperability systems allow end-users take advantage new technologies without need replace already installed systems pave way towards fully integrated security systems offering superior set features
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Computer security
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user-defined function user-defined function udf function provided user program environment context usual assumption functions built program environment old implementations basic programming language user-defined functions defined using def fn syntax modern dialects basic influenced structured programming paradigm code written user-defined functions procedures concept becomes practically redundant relational database management systems user-defined function provides mechanism extending functionality database server adding function evaluated standard query language usually sql statements standard distinguishes scalar table functions scalar function returns single value null whereas table function returns relational table comprising zero rows row one columns user-defined functions sql declared using codice_1 statement example function converts celsius fahrenheit might declared like created user-defined function may used expressions sql statements example invoked intrinsic functions allowed also includes select statements function used data stored tables database conceptually function evaluated per row usage example assume table named elements row known chemical element table column named boilingpoint boiling point element celsius query would retrieve name boiling point row invokes ctof user-defined function declared order convert value column value fahrenheit user-defined function carries certain properties characteristics sql standard defines following properties user-defined functions confused stored procedures stored procedures allow user group set sql commands procedure accept parameters execute sql statements depending parameters procedure expression thus used like user-defined functions database management systems allow creation user defined functions languages sql microsoft sql server example allows user use .net languages including c purpose db2 oracle support user-defined functions written c java programming languages three types udf microsoft sql server 2000 scalar functions inline table-valued functions multistatement table-valued functions scalar functions return single data value table returns clause scalar functions use scalar data types exception timestamp user-defined data types inline table-valued functions return result set single select statement multistatement table-valued functions return table built many transact-sql statements user-defined functions invoked query like built‑in functions object_id len datediff executed execute statement like stored procedures performance notes 1 microsoft sql server 2000 table-valued function wraps view may much faster view following myfunction example function-wrapper runs faster underlying view myview 2 microsoft sql server 2005 result code execution opposite view executed faster function-wrapper user-defined functions subroutines made one transact-sql statements used encapsulate code reuse takes zero arguments evaluates return value control-flow dml statements body similar stored procedures allow changes global session state like modifications database external resource file network support output parameter default keyword must specified pass default value parameter errors udf cause udf abort turn aborts statement invoked udf data type supported microsoft sql server 2000 like temporary table used store results mostly used define temporary variable type table return value udf scope limited function stored procedure batch defined assignment operation allowed table variables may used select insert update delete create function create udf alter function change characteristics udf drop function remove udf apache hive defines addition regular user defined functions udf also user defined aggregate functions udaf table-generating functions udtf hive enables developers create custom functions java
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Databases
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bidule bidule commercial software application creation interactive computer music multimedia produced canadian company plogue arts technology runs windows mac computers bidule uses modular structure based patch cord metaphor much like audiomulch reaktor pure data max/msp individual modules called bidules plogue web site states word bidule french thingy gadget set bidules connections called layout sub-patches called groups built within layouts saved use elsewhere program features real time audio midi open sound control osc spectral processing audio daw software rewire bidule run rewire mixer device bidule run standalone vst vsti au plugin host asio/coreaudio supported low latency audio bidule use multithread processing beta build discrete processing parameters linked midi osc input module parameters one hundred modules groups come software including modules perform high-level math signals
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Programming language topics
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trademark computer security trademark computer security contract code verifies security properties object code requires object certain security properties useful ensuring secure information flow object-oriented languages trademarking analogous signing data often implemented without cryptography trademark two operations operation analogous private key digital signature process must exposed untrusted code applied immutable objects makes sure verifytrademark called value returns true operation analogous public key digital signature process exposed untrusted code returns true if-and-only-if applytrademark called given object trademarking inverse taint checking whereas taint checking black-listing approach says certain objects trusted trademarking white-listing approach marks certain objects certain security properties apply trademark thought memoizing verification process sometimes verification process need done fact value particular security property verified statically case apply property used assert object produced code formally verified produce outputs particular security property one way applying trademark java
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Computer security
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insure++ insure++ memory debugger computer program used software developers detect various errors programs written c c++ made parasoft functionally similar memory debuggers purify valgrind dr memory insure++ automatically find erroneous accesses freed memory use-after-free situations array-bounds violations freeing unallocated memory often happens programmer frees memory twice frees global stack memory many others unlike purify valgrind insure++ inserts instrumentation source-code level allows detect errors tools miss particular insure++ detect buffer overflows automatic arrays overflows involve pointers accidentally jump one valid memory region another following example source-level instrumentation allows identify leak occurred occurred tools merely provide information memory allocated insure++ also gives stack trace when/where actual leak occurred additionally insure++ produce linear code sequence jump code coverage metrics tested code
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Operating systems
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visopsys visopsys visual operating system operating system written andy mclaughlin development operating system began 1997 operating system licensed gnu gpl headers libraries less restrictive lgpl license runs 32-bit ia-32 architecture features multitasking kernel supports asynchronous i/o fat line file systems requires pentium processor development visopsys began 1997 written andy mclaughlin first public release operating system 2 march 2001 version 0.1 release visopsys 32 bit operating system supporting preemptive multitasking virtual memory visopsys uses monolithic kernel written c programming language elements assembly language certain interactions hardware operating system sports graphical user interface small c library
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Operating systems
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st6 st7 st6 st7 8-bit microcontroller product lines stmicroelectronics commonly used small embedded applications like washing machines although use similar peripherals marketed part product line two architectures actually quite different 8-bit accumulator used operations plus two 8-bit index registers x used memory addressing also 8-bit instructions followed 2 bytes operands support manipulating branching individual bits memory similarities end st6 harvard architecture 8-bit 256 byte data address space separate 12-bit 4096 byte program space operands always 1 byte long instructions support two operands move 8-bit immediate 8-bit memory address subroutine calls done using separate hardware stack data registers program counter flags memory-mapped st6 addressing modes limited immediate 8-bit absolute memory address register indirect modes x st7 von neumann architecture single 16-bit 64 kib address space first 256 bytes ram zero page extra flexibility two-operand instructions except test bit branch registers memory-mapped uses general-purpose ram plus stack pointer register subroutine calls st7 supports wide variety addressing modes including base+index double-indirect st6 64 bytes ram 4096 bytes program rom larger amounts accessed bank-switching low 2k section rom ram address space actually 256 bytes divided follows mapped address space 12-bit program counter associated hardware stack four six levels deep depending model two status bits carry zero banked based processor mode separate status bits normal interrupt non-maskable interrupt operation first four general-purpose ram locations also known x v w registers instructions access using special short addressing modes x registers serve index registers use indirect addressing modes codice_1 codice_2 instruction set consists one byte opcode followed two one-byte operands instruction set summarized follows st7 six registers accumulator x index registers stack pointer program counter condition code register also double-indirect addressing allows zero page ram serve additional registers unusual useful feature interrupt pushes four registers stack x well usual pc cc interrupt return restores alu instructions fall two categories two-operand one-operand two-operand instructions use accumulator first source addressing mode specifies second source may destination usually accumulator instructions modify second source immediate operands forbidden cases one-operand instructions use specified operand source destination operand may register plus offset computes full-width sum 8-bit form may address memory 255+255 510 addition three prefix bytes may prepended instruction make sense
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Computer architecture
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dylan programming language dylan multi-paradigm programming language includes support functional object-oriented programming oop dynamic reflective providing programming model designed support generating efficient machine code including fine-grained control dynamic static behaviors created early 1990s group led apple computer concise thorough overview language may found dylan reference manual dylan derives scheme common lisp adds integrated object system derived common lisp object system clos dylan values including numbers characters functions classes first-class objects dylan supports multiple inheritance polymorphism multiple dispatch keyword arguments object introspection pattern-based syntax extension macros many advanced features programs express fine-grained control dynamism admitting programs occupy continuum dynamic static programming supporting evolutionary development allowing rapid prototyping followed incremental refinement optimization dylan main design goal dynamic language well-suited developing commercial software dylan attempts address potential performance issues introducing natural limits full flexibility lisp systems allowing compiler clearly understand compilable units libraries dylan derives much semantics scheme lisps dylan implementations initially built within extant lisp systems however dylan algol-like syntax instead lisp-like prefix syntax dylan created early 1990s group led apple computer one time development intended use apple newton computer dylan implementation reach sufficient maturity time newton instead used mix c newtonscript developed walter smith apple ended dylan development effort 1995 though made technology release version available apple dylan tr1 included advanced integrated development environment ide two groups contributed design language developed implementations harlequin released commercial ide microsoft windows carnegie mellon university released open source compiler unix systems called gwydion dylan implementations open source harlequin implementation named open dylan maintained group volunteers dylan hackers dylan language code-named ralph james joaquin chose name dylan dynamic language many dylan syntax features come lisp heritage originally dylan used lisp-like prefix syntax based s-expressions time language design completed syntax changed algol-like syntax expectation would familiar wider audience programmers syntax designed michael kahl described great detail dylan reference manual dylan case sensitive dylan lexical syntax allows use naming convention hyphen-minus signs used connect parts multiple-word identifiers sometimes called lisp-case kebab case convention common lisp languages used programming languages treat hyphen-minus part numeric literal single lexical token even surrounded whitespace characters identifiers dylan may contain special characters languages besides alphanumeric characters hyphen-minus signs dylan allows following non-alphanumerical characters part identifiers underscore codice_1 asterisk codice_2 ampersand codice_3 less-than sign codice_4 equals sign codice_5 greater-than sign codice_6 vertical bar codice_7 caret codice_8 dollar sign codice_9 percent sign codice_10 sign codice_11 identifiers may consist non-alphanumeric characters numeric characters alone ambiguity whitespace used simple class several slots convention classes named less-than greater-than signs used angle brackets e.g class named codice_12 code example codice_13 codice_14 codice_12 optional true codice_16 clauses example may write codice_17 codice_16 terminate codice_19 statement class rewritten minimal way possible slots typed codice_20 slots must initialized manually convention constant names begin factorial function codice_21 codice_22 normal identifiers explicit return statement result method function last expression evaluated common style leave semicolon expression return position many object-oriented languages classes main means encapsulation modularity class defines namespace controls definitions externally visible classes many languages define indivisible unit must used whole example using codice_23 concatenation function requires importing compiling codice_23 languages including dylan also include separate explicit namespace module system performs encapsulation general way dylan concepts compile-unit import-unit separated classes nothing specifically either library defines items compiled handled together module defines namespace classes placed together modules cut across programmer wishes often complete definition class exist single module spread across several optionally collected together different programs different definitions class including need example consider add-on library regex support codice_23 languages functionality included strings functionality must added codice_23 namespace soon occurs codice_23 class becomes larger functions n't need use regex still must pay increased library size reason sorts add-ons typically placed namespaces objects downside approach new functions longer part codice_23 instead isolated set functions must called separately instead codice_29 would natural organization oo viewpoint something like codice_30 used effectively reverses ordering dylan many interfaces defined code instance string concatenation method could placed string interface concat interface collects together different concatenation functions various classes commonly used math libraries functions tend applicable widely differing object types practical use interface construct build public private versions module something languages include bolt feature invariably causes problems adds syntax dylan every function call simply places private development interface collect publicly accessible functions codice_31 java c++ visibility object defined code meaning support similar change programmer would forced rewrite definitions fully could two versions time classes dylan describe codice_32 data members fields ivars etc objects fashion similar oo languages access slots via methods smalltalk default getter setter methods automatically generated based slot names contrast oo languages methods applicable class often defined outside class thus class definitions dylan typically include definition storage instance define class window view end class example class codice_33 defined class name syntax convention make class names stand out—the angle brackets merely part class name contrast languages convention capitalize first letter class name prefix name c example codice_33 inherits single class codice_35 contains two slots codice_36 holding string window title codice_37 holding x-y point corner window example title given default value position optional init-keyword syntax allows programmer specify initial value slot instantiating object class languages c++ java class would also define interface case definition explicit instructions languages access slots methods considered codice_38 meaning used subclasses allow unrelated code use window instances must declared codice_39 dylan sorts visibility rules considered part code module/interface system adds considerable flexibility instance one interface used early development could declare everything public whereas one used testing deployment could limit c++ java changes would require changes source code people wo n't whereas dylan fully unrelated concept although example use dylan also supports multiple inheritance dylan methods intrinsically associated specific class methods thought existing outside classes like clos dylan based multiple dispatch multimethods specific method called chosen based types arguments method need known compile time understanding required function may available based user preferences java methods would isolated specific class use functionality programmer forced import class refer explicitly call method class unavailable unknown compile time application simply wo n't compile dylan code isolated storage functions many classes methods call functions thereby looking feeling like oo languages however code may also located generic functions meaning attached specific class called natively anyone linking specific generic function method class accomplished thusly define method turn-blue w window end method definition similar languages would likely encapsulated within codice_33 class note setter call syntactic sugar codice_41 utility generic methods comes consider generic examples instance one common function languages codice_42 returns human-readable form object instance window might return title position parens string would return dylan methods could collected single module called codice_42 thereby removing code definition class specific object support codice_42 could easily added codice_42 module whole concept might strike readers odd code handle codice_42 window n't defined codice_33 might make sense consider dylan handles call codice_42 languages program compiled codice_42 codice_33 looked replaced pointer less method dylan occurs program first run runtime builds table method-name/parameters details looks methods dynamically via table means function specific method located anywhere compile-time unit end programmer given considerable flexibility terms place code collecting along class lines appropriate functional lines implication programmer add functionality existing classes defining functions separate file instance might wish add spell checking codice_51s languages would require access source code string class—and basic classes rarely given source form dylan extensible languages spell checking method could added codice_52 module defining classes applied via codice_53 construct case actual functionality might defined single generic function takes string returns errors codice_52 module compiled program strings objects get added functionality apple dylan implementation dylan produced apple computer originally developed apple newton product
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Programming language topics
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dublin core dublin core schema small set vocabulary terms used describe digital resources video images web pages etc well physical resources books cds objects like artworks full set dublin core metadata terms found dublin core metadata initiative dcmi website original set 15 classic metadata terms known dublin core metadata element set dcmes endorsed following standards documents dublin core metadata may used multiple purposes simple resource description combining metadata vocabularies different metadata standards providing interoperability metadata vocabularies linked data cloud semantic web implementations dublin refers dublin ohio usa schema originated 1995 invitational oclc/ncsa metadata workshop hosted oclc online computer library center library consortium based dublin national center supercomputing applications ncsa core refers metadata terms broad generic usable describing wide range resources semantics dublin core established maintained international cross-disciplinary group professionals librarianship computer science text encoding museums related fields scholarship practice starting 2000 dublin core community focused application profiles – idea metadata records would use dublin core together specialized vocabularies meet particular implementation requirements time world wide web consortium work generic data model metadata resource description framework rdf maturing part extended set dcmi metadata terms dublin core became one popular vocabularies use rdf recently context linked data movement dublin core metadata initiative dcmi provides open forum development interoperable online metadata standards broad range purposes business models dcmi activities include consensus-driven working groups global conferences workshops standards liaison educational efforts promote widespread acceptance metadata standards practices 2008 dcmi separated oclc incorporated independent entity currently changes made dublin core standard reviewed dcmi usage board within context dcmi namespace policy dcmi-namespace policy describes terms assigned also sets limits amount editorial changes allowed labels definitions usage comments dublin core standard originally included two levels simple qualified simple dublin core comprised 15 elements qualified dublin core included three additional elements audience provenance rightsholder well group element refinements also called qualifiers could refine semantics elements ways may useful resource discovery since 2012 two incorporated dcmi metadata terms single set terms using rdf data model full set elements found namespace http //purl.org/dc/terms/ definition terms often contains domains ranges may compatible pre-rdf definitions used original 15 dublin core elements separate namespace original 15 elements previously defined http //purl.org/dc/elements/1.1/ original dcmes version 1.1 consists 15 metadata elements defined way original specification dublin core element optional may repeated dcmi established standard ways refine elements encourage use encoding vocabulary schemes prescribed order dublin core presenting using elements dublin core became niso standards z39.85 ietf rfc 5013 2007 iso 15836 standard 2009 used base-level data element set description learning resources iso/iec 19788-2 metadata learning resources mlr – part 2 dublin core elements prepared iso/iec jtc1 sc36 full information element definitions term relationships found dublin core metadata registry archive form web page webcite says part metadata optional dublin core elements ... superseded 2008 dcmi metadata terms subsequent specification original 15 elements ongoing process develop exemplary terms extending refining dcmes begun additional terms identified generally working groups dcmi judged dcmi usage board conformance principles good practice qualification dublin core metadata elements element refinements make meaning element narrower specific refined element shares meaning unqualified element restricted scope guiding principle qualification dublin core elements colloquially known dumb-down principle states application understand specific element refinement term able ignore qualifier treat metadata value unqualified broader element may result loss specificity remaining element value without qualifier continue generally correct useful discovery addition element refinements qualified dublin core includes set recommended encoding schemes designed aid interpretation element value schemes include controlled vocabularies formal notations parsing rules value expressed using encoding scheme may thus token selected controlled vocabulary example term classification system set subject headings string formatted accordance formal notation example 2000-12-31 iso standard expression date encoding scheme understood application value may still useful human reader audience provenance rightsholder elements part simple dublin core 15 elements use audience provenance rightsholder using qualified dublin core dcmi also maintains small general vocabulary recommended use within element type vocabulary currently consists 12 terms dcmi metadata terms lists current set dublin core vocabulary set includes fifteen terms dcmes italic well qualified terms term unique uri namespace http //purl.org/dc/terms defined rdf properties syntax choices metadata expressed dublin core elements depend context dublin core concepts semantics designed syntax independent apply variety contexts long metadata form suitable interpretation machines people dublin core abstract model provides reference model particular dublin core encoding guidelines compared independent particular encoding syntax reference model helps implementers get better understanding kinds descriptions trying encode facilitates development better mappings translations different syntaxes one document type definition based dublin core open source metadata framework omf specification omf turn used rarian superseding scrollkeeper used gnome desktop kde help browsers scrollserver documentation server pbcore also based dublin core zope cmf metadata products used plone erp5 nuxeo cps content management systems simpledl fedora commons also implement dublin core epub e-book format uses dublin core metadata opf file
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Computer architecture
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