计算机英文参考文献.docx
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计算机英文参考文献.docx
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计算机英文参考文献
ProgressinComputers
PrestigeLecturedeliveredtoIEE,Cambridge,on5February2004
MauriceWilkes
ComputerLaboratory
UniversityofCambridge
Thefirststoredprogramcomputersbegantoworkaround1950.TheonewebuiltinCambridge,theEDSACwasfirstusedinthesummerof1949.
Theseearlyexperimentalcomputerswerebuiltbypeoplelikemyselfwithvaryingbackgrounds.Weallhadextensiveexperienceinelectronicengineeringandwereconfidentthatthatexperiencewouldstandusingoodstead.Thisprovedtrue,althoughwehadsomenewthingstolearn.Themostimportantofthesewasthattransientsmustbetreatedcorrectly;whatwouldcauseaharmlessflashonthescreenofatelevisionsetcouldleadtoaseriouserrorinacomputer.
Asfarascomputingcircuitswereconcerned,wefoundourselveswithanembarassderichess.Forexample,wecouldusevacuumtubediodesforgatesaswedidintheEDSACorpentodeswithcontrolsignalsonbothgrids,asystemwidelyusedelsewhere.Thissortofchoicepersistedandthetermfamiliesoflogiccameintouse.ThosewhohaveworkedinthecomputerfieldwillrememberTTL,ECLandCMOS.Ofthese,CMOShasnowbecomedominant.
Inthoseearlyyears,theIEEwasstilldominatedbypowerengineeringandwehadtofightanumberofmajorbattlesinordertogetradioengineeringalongwiththerapidlydevelopingsubjectofelectronics.dubbedintheIEElightcurrentelectricalengineering.properlyrecognisedasanactivityinitsownright.Irememberthatwehadsomedifficultyinorganisingaconferencebecausethepowerengineers’waysofdoingthingswerenotourways.AminorsourceofirritationwasthatallIEEpublishedpaperswereexpectedtostartwithalengthystatementofearlierpractice,somethingdifficulttodowhentherewasnoearlierpractice
Consolidationinthe1960s
Bythelate50sorearly1960s,theheroicpioneeringstagewasoverandthecomputerfieldwasstartingupinrealearnest.Thenumberofcomputersintheworldhadincreasedandtheyweremuchmorereliablethantheveryearlyones.Tothoseyearswecanascribethefirststepsinhighlevellanguagesandthefirstoperatingsystems.Experimentaltime-sharingwasbeginning,andultimatelycomputergraphicswastocomealong.
Aboveall,transistorsbegantoreplacevacuumtubes.Thischangepresentedaformidablechallengetotheengineersoftheday.Theyhadtoforgetwhattheyknewaboutcircuitsandstartagain.Itcanonlybesaidthattheymeasuredupsuperblywelltothechallengeandthatthechangecouldnothavegonemoresmoothly.
Soonitwasfoundpossibletoputmorethanonetransistoronthesamebitofsilicon,andthiswasthebeginningofintegratedcircuits.Astimewenton,asufficientlevelofintegrationwasreachedforonechiptoaccommodateenoughtransistorsforasmallnumberofgatesorflipflops.Thisledtoarangeofchipsknownasthe7400series.Thegatesandflipflopswereindependentofoneanotherandeachhaditsownpins.Theycouldbeconnectedbyoff-chipwiringtomakeacomputeroranythingelse.
Thesechipsmadeanewkindofcomputerpossible.Itwascalledaminicomputer.Itwassomethinglessthatamainframe,butstillverypowerful,andmuchmoreaffordable.Insteadofhavingoneexpensivemainframeforthewholeorganisation,abusinessorauniversitywasabletohaveaminicomputerforeachmajordepartment.
Beforelongminicomputersbegantospreadandbecomemorepowerful.Theworldwashungryforcomputingpowerandithadbeenveryfrustratingforindustrynottobeabletosupplyitonthescalerequiredandatareasonablecost.Minicomputerstransformedthesituation.
Thefallinthecostofcomputingdidnotstartwiththeminicomputer;ithadalwaysbeenthatway.ThiswaswhatImeantwhenIreferredinmyabstracttoinflationinthecomputerindustry‘goingtheotherway’.Astimegoesonpeoplegetmorefortheirmoney,notless.
ResearchinComputerHardware.
ThetimethatIamdescribingwasawonderfuloneforresearchincomputerhardware.Theuserofthe7400seriescouldworkatthegateandflip-floplevelandyettheoveralllevelofintegrationwassufficienttogiveadegreeofreliabilityfarabovethatofdiscreettransistors.Theresearcher,inauniversityorelsewhere,couldbuildanydigitaldevicethatafertileimaginationcouldconjureup.IntheComputerLaboratorywebuilttheCambridgeCAP,afull-scaleminicomputerwithfancycapabilitylogic.
The7400serieswasstillgoingstronginthemid1970sandwasusedfortheCambridgeRing,apioneeringwide-bandlocalareanetwork.PublicationofthedesignstudyfortheRingcamejustbeforetheannouncementoftheEthernet.Untilthesetwosystemsappeared,usershadmostlybeencontentwithteletype-basedlocalareanetworks.
Ringsneedhighreliabilitybecause,asthepulsesgorepeatedlyroundthering,theymustbecontinuallyamplifiedandregenerated.Itwasthehighreliabilityprovidedbythe7400seriesofchipsthatgaveusthecourageneededtoembarkontheprojectfortheCambridgeRing.
TheRISCMovementandItsAftermath
Earlycomputershadsimpleinstructionsets.Astimewentondesignersofcommerciallyavailablemachinesaddedadditionalfeatureswhichtheythoughtwouldimproveperformance.Fewcomparativemeasurementsweredoneandonthewholethechoiceoffeaturesdependeduponthedesigner’sintuition.
In1980,theRISCmovementthatwastochangeallthisbrokeontheworld.ThemovementopenedwithapaperbyPattersonandDitzelentitledTheCasefortheReducedInstructionsSetComputer.
Apartfromleadingtoastrikingacronym,thistitleconveyslittleoftheinsightsintoinstructionsetdesignwhichwentwiththeRISCmovement,inparticularthewayitfacilitatedpipelining,asystemwherebyseveralinstructionsmaybeindifferentstagesofexecutionwithintheprocessoratthesametime.Pipeliningwasnotnew,butitwasnewforsmallcomputers
TheRISCmovementbenefitedgreatlyfrommethodswhichhadrecentlybecomeavailableforestimatingtheperformancetobeexpectedfromacomputerdesignwithoutactuallyimplementingit.Irefertotheuseofapowerfulexistingcomputertosimulatethenewdesign.Bytheuseofsimulation,RISCadvocateswereabletopredictwithsomeconfidencethatagoodRISCdesignwouldbeabletoout-performthebestconventionalcomputersusingthesamecircuittechnology.Thispredictionwasultimatelybornoutinpractice.
Simulationmaderapidprogressandsooncameintouniversalusebycomputerdesigners.Inconsequence,computerdesignhasbecomemoreofascienceandlessofanart.Today,designersexpecttohavearoomfulof,computersavailabletodotheirsimulations,notjustone.Theyrefertosucharoomfulbytheattractivenameofcomputerfarm.
Thex86InstructionSet
Littleisnowheardofpre-RISCinstructionsetswithonemajorexception,namelythatoftheIntel8086anditsprogeny,collectivelyreferredtoasx86.ThishasbecomethedominantinstructionsetandtheRISCinstructionsetsthatoriginallyhadaconsiderablemeasureofsuccessarehavingtoputupahardfightforsurvival.
Thisdominanceofx86disappointspeoplelikemyselfwhocomefromtheresearchwings.bothacademicandindustrial.ofthecomputerfield.Nodoubt,businessconsiderationshavealottodowiththesurvivalofx86,butthereareotherreasonsaswell.Howevermuchweresearchorientedpeoplewouldliketothinkotherwise.highlevellanguageshavenotyeteliminatedtheuseofmachinecodealtogether.Weneedtokeepremindingourselvesthatthereismuchtobesaidforstrictbinarycompatibilitywithprevioususagewhenthatcanbeattained.Nevertheless,thingsmighthavebeendifferentifIntel’smajorattempttoproduceagoodRISCchiphadbeenmoresuccessful.Iamreferringtothei860(notthei960,whichwassomethingdifferent).Inmanywaysthei860wasanexcellentchip,butitssoftwareinterfacedidnotfitittobeusedinaworkstation.
Thereisaninterestingstinginthetailofthisapparentlyeasytriumphofthex86instructionset.ItprovedimpossibletomatchthesteadilyincreasingspeedofRISCprocessorsbydirectimplementationofthex86instructionsetashadbeendoneinthepast.Instead,designerstookaleafoutoftheRISCbook;althoughitisnotobvious,onthesurface,amodernx86processorchipcontainshiddenwithinitaRISC-styleprocessorwithitsowninternalRISCcoding.Theincomingx86codeis,aftersuitablemassaging,convertedintothisinternalcodeandhandedovertotheRISCprocessorwherethecriticalexecutionisperformed.
InthissummingupoftheRISCmovement,IrelyheavilyonthelatesteditionofHennessyandPatterson’sbooksoncomputerdesignasmysupportingauthority;seeinparticularComputerArchitecture,thirdedition,2003,pp146,151-4,157-8.
TheIA-64instructionset.
Sometimeago,IntelandHewlett-PackardintroducedtheIA-64instructionset.Thiswasprimarilyintendedtomeetagenerallyrecognisedneedfora64bitaddressspace.Inthis,itfollowedtheleadofthedesignersoftheMIPSR4000andAlpha.HoweveronewouldhavethoughtthatIntelwouldhavestressedcompatibilitywiththex86;thepuzzleisthattheydidtheexactopposite.
Moreover,builtintothedesignofIA-64isafeatureknownaspredicationwhichmakesitincompatibleinamajorwaywithallotherinstructionsets.Inparticular,itneeds6extrabitswitheachinstruction.Thisupsetsthetraditionalbalancebetweeninstructionwordlengthandinformationcontent,anditchangessignificantlythebriefofthecompilerwriter.
Inspiteofhavinganentirelynewinstructionset,IntelmadethepuzzlingclaimthatchipsbasedonIA-64wouldbe
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