计算机英语CPU.docx

计算机英语CPU.docx

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计算机英语CPU

Centralprocessingunit

DieofanIntel80486DX2microprocessor（actualsize:

12×6.75 mm）initspackaging.

Thecentralprocessingunit（CPU）istheportionofacomputersystemthatcarriesouttheinstructionsofacomputerprogram,andistheprimaryelementcarryingoutthecomputer'sfunctions.Thecentralprocessingunitcarriesouteachinstructionoftheprograminsequence,toperformthebasicarithmetical,logical,andinput/outputoperationsofthesystem.Thistermhasbeeninuseinthecomputerindustryatleastsincetheearly1960s.[1]Theform,designandimplementationofCPUshavechangeddramaticallysincetheearliestexamples,buttheirfundamentaloperationremainsmuchthesame.

EarlyCPUswerecustom-designedasapartofalarger,sometimesone-of-a-kind,computer.However,thiscostlymethodofdesigningcustomCPUsforaparticularapplicationhaslargelygivenwaytothedevelopmentofmass-producedprocessorsthataremadeforoneormanypurposes.Thisstandardizationtrendgenerallybeganintheeraofdiscretetransistormainframesandminicomputersandhasrapidlyacceleratedwiththepopularizationoftheintegratedcircuit（IC）.TheIChasallowedincreasinglycomplexCPUstobedesignedandmanufacturedtotolerancesontheorderofnanometers.BoththeminiaturizationandstandardizationofCPUshaveincreasedthepresenceofthesedigitaldevicesinmodernlifefarbeyondthelimitedapplicationofdedicatedcomputingmachines.Modernmicroprocessorsappearineverythingfromautomobilestocellphonesandchildren'stoys.

Contents

[hide]

∙1History

o1.1DiscretetransistorandintegratedcircuitCPUs

o1.2Microprocessors

∙2Operation

∙3Designandimplementation

o3.1Integerrange

o3.2Clockrate

o3.3Parallelism

▪3.3.1Instructionlevelparallelism

▪3.3.2Thread-levelparallelism

▪3.3.3Dataparallelism

∙4Performance

∙5Seealso

∙6Notes

∙7References

∙8Externallinks

History

Mainarticle:

HistoryofgeneralpurposeCPUs

EDVAC,oneofthefirstelectronicstoredprogramcomputers.

ComputerssuchastheENIAChadtobephysicallyrewiredinordertoperformdifferenttasks,whichcausedthesemachinestobecalled"fixed-programcomputers."Sincetheterm"CPU"isgenerallydefinedasasoftware（computerprogram）executiondevice,theearliestdevicesthatcouldrightlybecalledCPUscamewiththeadventofthestored-programcomputer.

Theideaofastored-programcomputerwasalreadypresentinthedesignofJ.PresperEckertandJohnWilliamMauchly'sENIAC,butwasinitiallyomittedsothemachinecouldbefinishedsooner.OnJune30,1945,beforeENIACwascompleted,mathematicianJohnvonNeumanndistributedthepaperentitledFirstDraftofaReportontheEDVAC.Itoutlinedthedesignofastored-programcomputerthatwouldeventuallybecompletedinAugust1949.[2]EDVACwasdesignedtoperformacertainnumberofinstructions（oroperations）ofvarioustypes.TheseinstructionscouldbecombinedtocreateusefulprogramsfortheEDVACtorun.Significantly,theprogramswrittenforEDVACwerestoredinhigh-speedcomputermemoryratherthanspecifiedbythephysicalwiringofthecomputer.ThisovercameaseverelimitationofENIAC,whichwastheconsiderabletimeandeffortrequiredtoreconfigurethecomputertoperformanewtask.WithvonNeumann'sdesign,theprogram,orsoftware,thatEDVACrancouldbechangedsimplybychangingthecontentsofthecomputer'smemory.

WhilevonNeumannismostoftencreditedwiththedesignofthestored-programcomputerbecauseofhisdesignofEDVAC,othersbeforehim,suchasKonradZuse,hadsuggestedandimplementedsimilarideas.Theso-calledHarvardarchitectureoftheHarvardMarkI,whichwascompletedbeforeEDVAC,alsoutilizedastored-programdesignusingpunchedpapertaperatherthanelectronicmemory.ThekeydifferencebetweenthevonNeumannandHarvardarchitecturesisthatthelatterseparatesthestorageandtreatmentofCPUinstructionsanddata,whiletheformerusesthesamememoryspaceforboth.MostmodernCPUsareprimarilyvonNeumannindesign,butelementsoftheHarvardarchitecturearecommonlyseenaswell.

Asadigitaldevice,aCPUislimitedtoasetofdiscretestates,andrequiressomekindofswitchingelementstodifferentiatebetweenandchangestates.Priortocommercialdevelopmentofthetransistor,electricalrelaysandvacuumtubes（thermionicvalves）werecommonlyusedasswitchingelements.Althoughthesehaddistinctspeedadvantagesoverearlier,purelymechanicaldesigns,theywereunreliableforvariousreasons.Forexample,buildingdirectcurrentsequentiallogiccircuitsoutofrelaysrequiresadditionalhardwaretocopewiththeproblemofcontactbounce.Whilevacuumtubesdonotsufferfromcontactbounce,theymustheatupbeforebecomingfullyoperational,andtheyeventuallyceasetofunctionduetoslowcontaminationoftheircathodesthatoccursinthecourseofnormaloperation.Ifatube'svacuumsealleaks,assometimeshappens,cathodecontaminationisaccelerated.Usually,whenatubefailed,theCPUwouldhavetobediagnosedtolocatethefailedcomponentsoitcouldbereplaced.Therefore,earlyelectronic（vacuumtubebased）computersweregenerallyfasterbutlessreliablethanelectromechanical（relaybased）computers.

TubecomputerslikeEDVACtendedtoaverageeighthoursbetweenfailures,whereasrelaycomputerslikethe（slower,butearlier）HarvardMarkIfailedveryrarely.[1]Intheend,tubebasedCPUsbecamedominantbecausethesignificantspeedadvantagesaffordedgenerallyoutweighedthereliabilityproblems.MostoftheseearlysynchronousCPUsranatlowclockratescomparedtomodernmicroelectronicdesigns（seebelowforadiscussionofclockrate）.Clocksignalfrequenciesrangingfrom100kHzto4 MHzwereverycommonatthistime,limitedlargelybythespeedoftheswitchingdevicestheywerebuiltwith.

DiscretetransistorandintegratedcircuitCPUs

CPU,corememory,andexternalbusinterfaceofaDECPDP-8/I.madeofmedium-scaleintegratedcircuits

ThedesigncomplexityofCPUsincreasedasvarioustechnologiesfacilitatedbuildingsmallerandmorereliableelectronicdevices.Thefirstsuchimprovementcamewiththeadventofthetransistor.TransistorizedCPUsduringthe1950sand1960snolongerhadtobebuiltoutofbulky,unreliable,andfragileswitchingelementslikevacuumtubesandelectricalrelays.WiththisimprovementmorecomplexandreliableCPUswerebuiltontooneorseveralprintedcircuitboardscontainingdiscrete（individual）components.

Duringthisperiod,amethodofmanufacturingmanytransistorsinacompactspacegainedpopularity.Theintegratedcircuit（IC）allowedalargenumberoftransistorstobemanufacturedonasinglesemiconductor-baseddie,or"chip."Atfirstonlyverybasicnon-specializeddigitalcircuitssuchasNORgateswereminiaturizedintoICs.CPUsbaseduponthese"buildingblock"ICsaregenerallyreferredtoas"small-scaleintegration"（SSI）devices.SSIICs,suchastheonesusedintheApolloguidancecomputer,usuallycontainedtransistorcountsnumberinginmultiplesoften.TobuildanentireCPUoutofSSIICsrequiredthousandsofindividualchips,butstillconsumedmuchlessspaceandpowerthanearlierdiscretetransistordesigns.Asmicroelectronictechnologyadvanced,anincreasingnumberoftransistorswereplacedonICs,thusdecreasingthequantityofindividualICsneededforacompleteCPU.MSIandLSI（medium-andlarge-scaleintegration）ICsincreasedtransistorcountstohundreds,andthenthousands.

In1964IBMintroduceditsSystem/360computerarchitecturewhichwasusedinaseriesofcomputersthatcouldrunthesameprogramswithdifferentspeedandperformance.Thiswassignificantatatimewhenmostelectroniccomputerswereincompatiblewithoneanother,eventhosemadebythesamemanufacturer.Tofacilitatethisimprovement,IBMutilizedtheconceptofamicroprogram（oftencalled"microcode"）,whichstillseeswidespreadusageinmodernCPUs.[3]TheSystem/360architecturewassopopularthatitdominatedthemainframecomputermarketfordecadesandleftalegacythatisstillcontinuedbysimilarmoderncomputersliketheIBMzSeries.Inthesameyear（1964）,DigitalEquipmentCorporation（DEC）introducedanotherinfluentialcomputeraimedatthescientificandresearchmarkets,thePDP-8.DECwouldlaterintroducetheextremelypopularPDP-11linethatoriginallywasbuiltwithSSIICsbutwaseventuallyimplementedwithLSIcomponentsoncethesebecamepractical.InstarkcontrastwithitsSSIandMSIpredecessors,thefirstLSIimplementationofthePDP-11containedaCPUcomposedofonlyfourLSIintegratedcircuits.[4]

Transistor-basedcomputershadseveraldistinctadvantagesovertheirpredecessors.Asidefromfacilitatingincreasedreliabilityandlowerpowerconsumption,transistorsalsoallowedCPUstooperateatmuchhigherspeedsbecauseoftheshortswitchingtimeofatransistorincomparisontoatubeorrelay.Thankstoboththeincreasedreliabilityaswellasthedramaticallyincreasedspeedoftheswitchingelements（whichwerealmostexclusivelytransistorsbythistime）,CPUclockratesinthetensofmegahertzwereobtainedduringthisperiod.AdditionallywhilediscretetransistorandICCPUswereinheavyusage,newhigh-performancedesignslikeSIMD（SingleInstructionMultipleData）vectorprocessorsbegantoappear.TheseearlyexperimentaldesignslatergaverisetotheeraofspecializedsupercomputerslikethosemadebyCrayInc.

Microprocessors

ThediefromanIntel8742

Intel80486DX2microprocessorinaceramicPGApackage.

Theintroductionofthemicroprocessorinthe1970ssignificantlyaffectedt