计算机专业文献翻译微处理器.docx

计算机专业文献翻译微处理器.docx

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计算机专业文献翻译微处理器

Microprocessors

Amicroprocessorisacomputationenginethatisfabricatedonasinglechip.ThefirstmicroprocessorwastheIntel4004,introducedin1971.The4004wasnotverypowerful–allitcoulddowasaddandsubtract,anditcouldonlydothat4bitsatatime.Butitwasamazingthateverythingwasononechip.Priortothe4004,engineersbuiltcomputerseitherfromcollectionsofchipsorfromdiscretecomponents.The4004poweredoneofthefirstportableelectroniccalculators.

ThefirstmicroprocessortomakeitintoahomecomputerwastheIntel8080,acomplete8-bitcomputeronthechip,introducedin1974.ThefirstmicroprocessortomakearealsplashinthemarketwastheIntel8088,introducedin1979andincorporatedintotheIBMPC.ThePCmarketmovedfromthe8088tothe80286tothe80386tothe80486tothePentiumtothePentiumIItothePentiumIIItothePentium4.AllofthesemicroprocessorsaremadebyIntelandallofthemareimprovementsonthebasicdesignofthe8088.ThePentium4canexecuteanypieceofcodethatranontheoriginal8088,butitdoesitabout5,000timesfaster!

ThefollowingtableshowsthedifferencesbetweenthedifferentprocessorsthatIntelhasintroducedovertheyears.

Table1.2

Name

Date

Transistors

Micron[1]

Clock

speed

Datawidth[2]

MIPS[3]

8080

1974

6,000

6

2MHz

8bits

0.64

8088

1979

29,000

3

5MHz

16bits

8-bitbus

0.33

80286

1982

134,000

1.5

6MHz

16bits

1

80386

1985

275,000

1.5

16MHz

32bits

5

80486

1989

1,200,000

1

25MHz

32bits

20

Pentium

1993

3,100,000

0.8

60MHz

32bits

64-bitbus

100

Pentium

1997

7,500,000

0.35

233MHz

32bits

64-bitbus

~300

Pentium

1999

9,500,000

0.25

450MHz

32bits

64-bitbus

~510

Pentium4

2000

42,000,000

0.18

1.5GHz

32bits

64-bitbus

~1,700

Fromthistableyoucanseethat,ingeneral,thereisarelationshipbetweenclockspeedandMIPS.Themaximumclockspeedisafunctionofthemanufacturingprocessanddelayswithinthechip.ThereisalsoarelationshipbetweenthenumberoftransistorsandMIPS.Forexample,the8088clockedat5MHzbutonlyexecutedat0.33MIPS（aboutoneinstructionper15clockcycles）.Modernprocessorscanoftenexecuteatarateoftwoinstructionsperclockcycle.Thatimprovementisdirectlyrelatedtothenumberoftransistorsonthechip.

InsideaMicroprocessorAmicroprocessorexecutesacollectionofmachineinstructionsthattelltheprocessorwhattodo.Basedontheinstruction,amicroprocessordoesthreebasicthings:

1.UsingitsALU（Arithmetic/LogicUnit）,amicroprocessorcanperformmathematicaloperationslikeaddition,subtraction,multiplicationanddivision.ModernMicroprocessorscontaincompletefloatingpointprocessorsthatcanperformextremelysophisticatedoperationsonlargefloatingpointnumbers.

2.Amicroprocessorcanmovedatafromonememorylocationtoanother.

3.Amicroprocessorcanmakedecisionsandjumptoanewsetofinstructionsbasedonthosedecisions.

Thesemaybeverysophisticatedthingsthatamicroprocessordoes,butthoseareitsthreebasicactivities.Thefollowingdiagramshowsanextremelysimplemicroprocessorcapableofdoingthosethreethings:

Thismicroprocessorhasanaddressbusthatsendsanaddresstomemory,adatabusthatcansenddatatomemoryorreceivedatafrommemory,anRD（read）andWR（write）linetotellthememorywhetheritwantstosetorgettheaddressedlocation,aclocklinethatletsaclockpulsesequencetheprocessorandareset[4]linethatresetstheprogramcountertozero（orwhatever）andrestartsexecution.Andlet’sassumethatboththeaddressanddatabusesare8bitswidehere.

Herearethecomponentsofthissimplemicroprocessor（Figure1.1）:

Figure1.1

1.RegistersA,BandCaresimplylatchesmadeoutofflip–flops.

2.TheaddresslatchisjustlikeregistersA,BandC.

3.Theprogramcounterisalatchwiththeextraabilitytoincrementby1whentoldtodoso,andalsotoresettozerowhentoldtodoso.

4.TheALUcouldbeassimpleasan8-bitadder,oritmightbeabletoadd,subtract,multiplyanddivide8–bitvalues.Let’sassumethelatterhere.

5.ThetestregisterisaspeciallatchthatcanholdvaluesfromcomparisonsperformedintheALU.AnALUcannormallycomparetwonumbersanddetermineiftheyareequal,ifoneisgreaterthantheother,etc.Thetestregistercanalsonormallyholdacarrybitfromthelaststageoftheadder.Itstoresthesevaluesinflip-flopsandthentheinstructiondecodercanusethevaluestomakedecisions.

6.Therearesixboxesmarked“3-State”inthediagram.Thesearetri-statebuffers[5].Atri-statebuffercanpassa1,a0oritcanessentiallydisconnectitsoutput.Atri-statebufferallowsmultipleoutputstoconnecttoawire,butonlyoneofthemtoactuallydrivea1ora0ontotheline.

7.Theinstructionregisterandinstructiondecoderareresponsibleforcontrollingalloftheothercomponents.

Althoughtheyarenotshowninthisdiagram,therewouldbecontrollinesfromtheinstructiondecoderthatwould:

1.TelltheAregistertolatchthevaluecurrentlyonthedatabus

2.TelltheBregistertolatchthevaluecurrentlyonthedatabus

3.TelltheCregistertolatchthevaluecurrentlyonthedatabus

4.Telltheprogramcounterregistertolatchthevaluecurrentlyonthedatabus

5.Telltheaddressregistertolatchthevaluecurrentlyonthedatabus

6.Telltheinstructionregistertolatchthevaluecurrentlyonthedatabus

7.Telltheprogramcountertoincrement

8.Telltheprogramcountertoresettozero

9.Activateanyofthesixtri-statebuffers（sixseparatelines）

10.TelltheALUwhatoperationtoperform

11.TellthetestregistertolatchtheALU’stestbibs

12.ActivatetheRDline

13.ActivatetheWRline

Comingintotheinstructiondecoderarethebitsfromthetestregisterandtheclockline,aswellasthebitsfromtheinstructionregister.

RAMandROMtheaddressanddatabuses,aswellastheRDandWRlinesconnecteithertoRAMorROM-generallyboth.Inoursamplemicroprocessor,wehaveanaddressbus8bitswideandadatabus8bitswide.Thatmeansthatthemicroprocessorcanaddress（28）256bytesofmemory,anditcanreadorwrite8bitsofthememoryatatime.Let’sassumethatthissimplemicroprocessorhas128bytesofROMstartingataddress0and128bytesofRAMstartingataddress128.

ROMstandsforread-onlymemory.AROMchipisprogrammedwithapermanentcollectionofpre-setbytes.TheaddressbustellstheROMchipwhichbytetogetandplaceonthedatabus.WhentheRDlinechangesstate,theROMchippresentstheselectedbyteontothedatabus.

RAMstandsforrandom-accessmemory.RAMcontainsbytesofinformation,andthemicroprocessorcanreadorwritetothosebytesdependingonwhethertheRDorWRlineissignaled.Oneproblemwithtoday’sRAMchipsisthattheyforgeteverythingoncethepowergoesoff.ThatiswhythecomputerneedsROM.

Bytheway,nearlyallcomputerscontainsomeamountofROM（itispossibletocreateasimplecomputerthatcontainsnoRAM-manymicrocontrollersdothisbyplacingahandfulofRAMbytesontheprocessorchipitself-butgenerallyimpossibletocreateonethatcontainsnoROM）.OnaPC,theROMiscalledtheBIOS（BasicInput/OutputSystem）.Whenthemicroprocessorstarts,itbeginsexecutinginstructionsitfindsintheBIOS.TheBIOSinstructionsdothingsliketestthehardwareinthemachine,andthenitgoestotheharddisktofetchthebootsector.Thisbootsectorisanothersmallprogram,andtheBIOSstoresitinRAMafterreadingitoffthedisk.Themicroprocessorthenbeginsexecutingthebootsector’sinstructionsfromRAM.ThebootsectorprogramwilltellthemicroprocessortofetchsomethingelsefromtheharddiskintoRAM,whichthemicroprocessorthenexecutes,andsoon.Thisishowthemicroprocessorloadsandexecutestheentireoperatingsystem.

MicroprocessorInstructionsEventheincrediblysimplemicroprocessorshownherewillhaveafairlylargesetofinstructionsthatitcanperform.Thecollectionofinstructionsisimplementedasbitpatterns,eachoneofwhichhasadifferentmeaningwhenloadedintotheinstructionregister.Humansarenotparticularlygoodatrememberingbitpatterns,soasetofshortwordsaredefinedtorepresentthedifferentbitpatterns.Thiscollectionofwordsiscalledtheassemblylanguageoftheprocessor.Anassemblercantranslatethewordsintotheirbitpatternsveryeasily,andthentheoutputoftheassemblerisplacedinmemoryforthemicroprocessortoexecute.IfyouuseClanguageprogramming,aCcompilerwilltranslatestheCcodeintoassemblylanguage.

Sonowthequestionis,“HowdoalloftheseinstructionslookinROM?

”Eachoftheseassemblylanguageinstructionsmustberepresentedbyabinarynumber.Thesenumbersareknownasopcodes.Theinstructiondecoderneedstoturneachoftheopcodesintoasetofsignalsthatdrivethedifferentcomponentsinsidethemicroprocessor.Let’staketheADDinstructionasanexampleandlookatwhatitneedstodo:

Duringthefirstclockcycle,weneedtoactuallyloadtheinstruction.Thereforetheinstructiondecoderneedsto:

Activatethetri-statebufferfortheprogramcounter

ActivatetheRDline

Activatethedata-intri-statebuffer

Latchtheinstructionintotheinstructionregister

Duringthesecondclockcycle,theADDinstructionisdecoded.Itneedstodoverylittle:

SettheoperationoftheALUtoaddition

LatchtheoutputoftheALUintotheCregister

Duringthethirdclockcycle,theprogramcounterisincremented（intheorythiscouldbeoverlappedintothesecondclockcycle）.

Everyinstru