电子信息工程专业专业英语三千字翻译汇编.docx
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电子信息工程专业专业英语三千字翻译汇编.docx
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电子信息工程专业专业英语三千字翻译汇编
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)Allmicroprocessordesignsseekbetterperformancewithinthelimitationsof
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