电子信息工程专业专业英语三千字翻译.docx

电子信息工程专业专业英语三千字翻译.docx

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电子信息工程专业专业英语三千字翻译

Unit3computerarchitectureandmicroprocessors

3--1ComputerArchitecture

1）Computerarchitecture,incomputerscience,isageneraltermreferringtothestructureofallorpartofcomputersystem.Thetermalsocoversthedesignofsystemsoftware,suchastheoperatingsystem（theprogramthatcontrolsthecomputer）,aswellasreferringtothecombinationofhardwareandbasicsoftwarethatlinksthemachinesonacomputernetwork.Computerarchitecturereferstoanentirestructureandtothedetailsneededtomakeitfunctional.Thus,computerarchitecturecoverscomputersystems,microprocessors,circuits,andsystemprograms.Typicallythetermdoesnotrefertoapplicationprograms,suchasspreadsheetsorwordprocessing,whicharerequiredtoperformataskbutnottomakethesystemrun.

2）1.DesignElements

3）Indesigningacomputersystem,architectsconsiderfivemajorelementsthatmakeupthesystem'shardware:

thearithmetic/logicunit,controlunit,memory,input,andoutput.Thearithmetic/logicunitperformsarithmeticandcomparesnumericalvalues.Thecontrolunitdirectstheoperationofthecomputerbytakingtheuserinstructionsandtransformingthemintoelectricalsignalsthatthecomputer'scircuitrycanunderstand.Thecombinationofthearithmetic/logicunitandthecontrolunitiscalledthecentralprocessingunit（CPU）.Thememorystoresinstructionsanddata.Theinputinputandoutputsectionsallowthecomputertoreceiveandsenddata,respectively.

4）Differenthardwarearchitecturesarerequiredbecauseofthespecializedneedsofsystemsandusers.Oneusermayneedasystemtodisplaygraphicsextremelyfast,whileanothersystemmayhavetobeoptimizedforsearchingadatabaseorconservingbatterypowerinalaptopcomputer.

5）Inadditiontothehardwaredesign,thearchitectsmustconsiderwhatsoftwareprogramswilloperatethesystem.Software,suchasprogramminglanguagesandoperatingsystems,makesthedetailsofthehardwarearchitectureinvisibletotheuser.Forexample,computersthatusetheCprogramminglanguageoraUNIToperatingsystemmayappearthesamefromtheuser'sviewpoint,althoughtheyusedifferenthardwarearchitectures.

6）2.ProcessingArchitecture

7）Whenacomputercarriesoutaninstruction,itproceedsthroughfivesteps.First,thecontrolunitretrievestheinstructionfrommemory,forexample,aninstructiontoaddtwonumbers.Second,thecontrolunitdecodestheinstructionintoelectronicsignalsthatcontrolthecomputer.Third,thecontrolunitfetchesthedata（thetwonumbers）.Fourth,thearithmetic/logicunitperformsthespecificoperation（theadditionofthetwonumbers）.Fifth,thecontrolunitsavestheresult（thesumofthetwonumbers）.

8）Earlycomputersusedonlysimpleinstructionsbecausethecostofelectroniccapableofcarryingoutcomplexinstructionswashigh.Asthiscostdecreasedinthe1960s,morecomplicatedinstructionsbecamepossible.Complexinstructions（singleinstructionsthatspecifymultipleoperations）cansavetimebecausetheymakeitunnecessaryforthecomputertoretrieveadditionalinstructions.Forexample,ifsevenoperationsarecombinedinoneinstruction,thensixofthestepsthatfetchinstructionsareeliminatedandthecomputerspendslesstimeprocessingthatoperation.Computersthatcombineseveralinstructionsintoasingleoperationarecalledcomplexinstructionsetcomputers（CISC）.

9）However,mostprogramsdonotoftenusecomplexinstructions,butconsistmostlyofsimpleinstructions.WhenthesesimpleinstructionsarerunonCISCarchitectures,theyslowdownprocessingbecauseeachinstruction--whethersimpleorcomplex--takeslongertodecodeinaCISCdesign.Analternativestrategyistoreturntodesignsthatuseonlysimple,single--operationinstructionsetsandmakethemostfrequentlyusedoperationsfasterinordertoincreaseoverallperformance.Computersthatfollowthisdesignarecalledreducedinstructionsetcomputers（RISC）.

10）RISCdesignsareespeciallyfastatthenumericalcomputationsrequiredinscience,graphics,andengineeringapplications.CISCdesignsarecommonlyusedfornon-numericalcomputationsbecausetheyprovidespecialinstructionsetsforhandlingcharacterdata,suchastextinawordprocessingprogram.SpecializedCISCarchitectures,calleddigitalsignalprocessors,existtoaccelerateprocessingofdigitizedaudioandvideosignals.

11）3.OpenandClosedArchitectures

12）TheCPUofacomputerisconnectedtomemoryandtotheoutsideworldbymeansofeitheranopenoraclosedarchitecture.Anopenarchitecturecanbeexpandedafterthesystemhasbeenbuilt,usuallybyaddingextracircuitry,suchasanewmicroprocessorcomputerchipconnectedtothemainsystem.Thespecificationsofthecircuitryaremadepublic,allowingothercompaniestomanufacturetheseexpansionproducts.

13）Closedarchitecturesareusuallyemployedinspecializedcomputersthatwillnotrequireexpansion,forexample,computersthatcontrolmicrowaveovens.Somecomputermanufacturershaveusedclosedarchitecturessothattheircustomerscanpurchaseexpansioncircuitryonlyfromthem.Thisallowsthemanufacturetochargemoreandreducestheoptionsfortheconsumer.

14）4.NetworkArchitecture

15）Computerscommunicatewithothercomputersvianetworks.Thesimplestnetworkisadirectconnectionbetweentwocomputers.However,computerscanalsobeconnectedoverlargenetworks,allowinguserstoexchangedata,communicateviaelectronicmail,andshareresourcessuchasprinters.

16）Computerscanbeconnectedinseveralways.Inaringconfiguration,dataaretransmittedalongtheringandeachcomputerintheringexaminesthisdatatodetermineifitistheintendedrecipient.Ifthedataarenotintendedforaparticularcomputer,thecomputerpassesthedatatothenextcomputerinthering.Thisprocessisrepeateduntilthedataarriveattheirintendeddestination.Aringnetworkallowsmultiplemessagestobecarriedsimultaneously,butsinceeachmessageischeckedbyeachcomputer,datatransmissionisslowed.

17）Inabusconfiguration,computersareconnectedthroughasinglesetofwires,calledabus.Onecomputersendsdatatoanotherbybroadcastingtheaddressofthereceiveandthedataoverthebus.Allthecomputersinthenetworklookattheaddresssimultaneously,andtheintendedrecipientacceptsthedata.Abusnetwork,unlikearingnetwork,allowsdatatobesentdirectlyfromonecomputertoanother.However,onlyonecomputeratatimecantransmitdata.Theothersmustwaittosendtheirmessages.

18）Inastarconfiguration,computersarelinkedtoacentralcomputercalledahub.Acomputersendstheaddressofthereceiverandthedatatothehub,whichthenlinksthesendingandreceivingcomputersdirectly.Astarnetworkallowsmultiplemessagestobesentsimultaneously,butitismorecostlybecauseitusesanadditionalcomputer,thehub,todirectthedata.

19）5.RecentAdvances

20）OneproblemincomputerarchitectureiscausedbythedifferencebetweenthespeedoftheCPUandthespeedatwhichmemorysuppliesinstructionsanddata.ModernCPUscanprocessinstructionsin3nanoseconds（3billionthsofasecond）.Atypicalmemoryaccess,however,takes100nanosecondsandeachinstructionmayrequiremultipleaccesses.Tocompensateforthisdisparity,newcomputerchipshavebeendesignedthatcontainsmallmemories,calledcaches,locatedneartheCPU.BecauseoftheirproximitytotheCPUandtheirsmallsize,cachescansupplyinstructionsanddatafasterthannormalmemory.Cachememorystoresthemostfrequentlyusedinstructionsanddataandcangreatlyincreaseefficiency.

21）Althoughalargecachememorycanholdmoredata,italsobecomesslower.Tocompensate,computerarchitectsemploydesignswithmultiplecaches.ThedesignplacesthesmallestandfastestcachenearesttheCPUandlocatesasecondlargeandslowercachefartheraway.ThisarrangementallowstheCPUtooperateonthemostfrequentlyaccessedinstructionsanddataattopspeedandtoslowdownonlyslightlywhenaccessingthesecondarycache.UsingseparatecachesforinstructionsanddataalsoallowstheCPUtoretrieveaninstructionanddatasimultaneously.

22）Antherstrategytoincreasespeedandefficiencyistheuseofmultiplearithmetic/logicunitsforsimultaneousoperations,calledsuperscalarexecution.Inthisdesign,instructionsareacquiredingroups.Thecontrolunitexamineseachgrouptoseeifitcontainsinstructionsthatcanbeperformedtogether.Somedesignsexecuteasmanyassixoperationssimultaneously.Itisrare,however,tohavethismanyinstructionsruntogether,soonaveragetheCPUdoesnotachieveasix-foldincreaseinperformance.

23）Multiplecomputersaresometimescombinedintosinglesystemscalledparallelprocessors.Whenamachinehasmorethanonethousandarithmetic/logicunits,itissaidtobemassivelyparallel.Suchmachinesareusedprimarilyfornumericallyintensivescientificandengineeringcomputation.Parallelmachinescontainingasmanyassixteenthousandcomputershavebeenconstructed.

3-3VLIWMicroprocessors

24）WhenTransmetaCorp.revealeditsnewCrusoeofprocessorslastmonth,expertsweren’tsurprisedtolearnthatthechipsarebasedonVeryLongInstructionWord（VLIW）technology.VLIWhasbecometheprevailingphilosophyofmicroprocessordesign,eclipsingolderapproachessuchasRISCandcomplexinstructionsetcomputing（CISC）.

25）Allmicroprocessordesignsseekbetterperformancewithinthelimitationsoft