計(jì)算機(jī)專業(yè)英語教程(第5版)翻譯完整版

計(jì)算機(jī)專業(yè)英語教程（第5版）翻譯完整版1.1ACloserLookattheProcessorandPrimaryStorage仔細(xì)看看處理器和主存儲(chǔ)器Wehavelearnedthatallcomputershavesimilarcapabilitiesandperformessentiallythesamefunctions,althoughsomemightbefasterthanothers.Wehavealsolearnedthatacomputersystemhasinput,output,storage,andprocessingcomponents;thattheprocessoristhe“intelligence”ofacomputersystem;andthatasinglecomputersystemmayhaveseveralprocessors.Wehavediscussedhowdataarerepresentedinsideacomputersysteminelectronicstatescalledbits.Wearenowreadytoexposetheinnerworkingsofthenucleusofthecomputersystem—theprocessor.我們已經(jīng)知道，所有的計(jì)算機(jī)都具有相似的能力，并且在本質(zhì)上執(zhí)行相同的功能，盡管一些可能會(huì)比另一些快一點(diǎn)。我們也知道，一個(gè)計(jì)算機(jī)系統(tǒng)具有輸入，輸出，存儲(chǔ)和處理部件；處理器是一個(gè)計(jì)算機(jī)系統(tǒng)智能核心，并且一個(gè)計(jì)算機(jī)系統(tǒng)可以有許多個(gè)處理器。我們已經(jīng)討論過如何在計(jì)算機(jī)系統(tǒng)內(nèi)部，用被稱作“位”的電子狀態(tài)來表現(xiàn)數(shù)據(jù)，現(xiàn)在我們要弄明白計(jì)算機(jī)系統(tǒng)的核心，即處理器，的內(nèi)在的工作方式。Theinternaloperationofacomputerisinteresting,buttherereallyisnomysterytoit.Themysteryisinthemindsofthosewholistentohearsayandbelievescience-fictionwriter.Thecomputerisanonthinkingelectronicdevicethathastobepluggedintoanelectricalpowersource,justlikeatoasteroralamp.計(jì)算機(jī)的內(nèi)部操作很有意思，但確實(shí)沒有什么神秘可言。所謂的神秘只是存在于些那聽信傳聞和相信科幻小說作家的人的意識(shí)中。計(jì)算機(jī)就是一種沒有思想的需要接通電源的電子設(shè)備而已，與烤面包機(jī)和臺(tái)燈差不多。1/8

Literallyhundredsofdifferenttypesofcomputersaremarketedbyscoresofmanufacturers[1].Thecomplexityofeachtypemayvaryconsiderably,butintheendeachprocessor,sometimescalledthecentralprocessingunitorCPU,hasonlytwofundamentalsections:thecontrolunitandthearithmeticandlogicunit.Primarystoragealsoplaysanintegralpartintheinternaloperationofaprocessor.Thesethree—primarystorage,thecontrolunit,andthearithmeticandlogicunit—worktogether.Let’slookattheirfunctionsandtherelationshipsbetweenthem.不加夸張地講，市場(chǎng)上有幾百種不同類型的計(jì)算機(jī)在銷售.每種電腦在復(fù)雜性上可能有很大區(qū)別，但歸根結(jié)底,每種處理器，有時(shí)稱為中央處理器即cpu，只有兩個(gè)基本部分:控制單元和計(jì)算邏輯單元.主內(nèi)存在處理器內(nèi)部操作中也是一個(gè)不可缺少的部分.這三個(gè)部件--主內(nèi)存，控制單元和計(jì)算邏輯單元--一起工作.然我們看看它們(各自的)功能和它們之間的聯(lián)系。Unlikemagneticsecondarystoragedevices,suchastapeanddisk,primarystoragehasnomovingparts.Withnomechanicalmovement,datacanbeaccessedfromprimarystorageatelectronicspeeds,orclosetothespeedoflight.Mostoftoday’scomputersuseDRAM(DynamicRandom-AccessMemory)technologyforprimarystorage.Astate-of-the-artDRAMchipaboutoneeighththesizeofapostagestampcanstoreabout256,000,000bits,orover25,600,000charactersofdata!主存與其他的輔助存儲(chǔ)器（如：磁帶、硬盤）不一樣的是，主存不含有運(yùn)轉(zhuǎn)部件。由于沒有機(jī)械運(yùn)轉(zhuǎn)的需要，主存種數(shù)據(jù)訪問可以達(dá)到電子的速，度或接近于光速。當(dāng)今計(jì)算機(jī)的主存大多數(shù)使用DRAM（動(dòng)態(tài)隨機(jī)存取存儲(chǔ)器）技術(shù)。目前最新的工藝水平是：一塊只有大約1/8張郵票大小的DRAM芯片卻可以存儲(chǔ)大約256,000,000位，約25,6000,000個(gè)字符的數(shù)據(jù)。Primarystorage,ormainmemory,providestheprocessorwithtemporarystorageforprogramsanddata.Allprogramsanddatamustbetransferredtoprimarystoragefromaninputdevice(suchasaVDT)orfromsecondary2/8

storage(suchasadisk)beforeprogramscanbeexecutedordatacanbeprocessed.Primarystoragespaceisalwaysatapremium;therefore,afteraprogramhasbeenexecuted,thestoragespaceitoccupiedisreallocatedtoanotherprogramawaitingexecution.主存儲(chǔ)器，也就是說內(nèi)存，用于為處理器暫時(shí)存放程序和數(shù)據(jù)。所有的程序和數(shù)據(jù)在被操作之前必須從輸入設(shè)備（如VDT）或者輔助存儲(chǔ)器轉(zhuǎn)存到主存儲(chǔ)器中。主存儲(chǔ)器存儲(chǔ)容量通常是相當(dāng)有限的，因此，在一個(gè)程序執(zhí)行結(jié)束，它所占用的存儲(chǔ)空間必須被重新分配給其它正在等待執(zhí)行操作的程序。Figure1-1illustrateshowallinput/output(I/O)is“readto”or“writtenfrom”primarystorage.Inthefigure,aninquiry(input)ismadeonaVDT.Theinquiry,intheformofamessage,isroutedtoprimarystorageoverachannel(suchasacoaxialcable).Themessageisinterpreted,andtheprocessorinitiatesactiontoretrievetheappropriateprogramanddatafromsecondarystorage[3].Theprogramanddataare“l(fā)oaded”,ormoves,toprimarystoragefromsecondarystorage.Thisisanondestructivereadprocess.Thatis,theprogramanddatathatarereadresideinbothprimarystorage(temporarily)andsecondarystorage(permanently).Thedataaremanipulatedaccordingtoprograminstructions,andareportiswrittenfromprimarystoragetoaprinter.圖1-1描述了輸入/輸出設(shè)備與主存儲(chǔ)器間的讀和寫過程。在圖中，VDT發(fā)出一個(gè)輸入請(qǐng)求，請(qǐng)求是以消息模式通過通道（如同軸電纜）發(fā)送到主存儲(chǔ)器。這個(gè)查詢被解釋，處理器發(fā)起操作從輔助存儲(chǔ)器中調(diào)用合適的程序和數(shù)據(jù)。程序和數(shù)據(jù)從輔助存儲(chǔ)器傳送到主存儲(chǔ)器中，這是一個(gè)非破壞性的讀取過程，也就是說，程序和數(shù)據(jù)同時(shí)存在于主存（臨時(shí)保存）和輔助存儲(chǔ)器（永久保存）中。根據(jù)程序指令的指示，處理器對(duì)數(shù)據(jù)進(jìn)行操作，從并主存?zhèn)魉鸵环輬?bào)告到打印機(jī)。Aprograminstructionorapieceofdataisstoredinaspecificprimarystoragelocationcalledanaddress.Addressespermitprograminstructionsanddatatobelocated,accessed,andprocessed.Thecontentofeach3/8

addressisconstantlychangingasdifferentprogramsareexecutedandnewdataareprocessed.程序指令和數(shù)據(jù)是存儲(chǔ)在主存中一個(gè)特殊的位置，稱為地址空間。通過地址空間可以實(shí)現(xiàn)計(jì)算機(jī)對(duì)程序指令和數(shù)據(jù)的定位、訪問和處理。地址空間的內(nèi)容是經(jīng)常變化的，這是由于計(jì)算機(jī)一直在執(zhí)行不同的程序和數(shù)據(jù)。Anothernameforprimarystorageisrandom-accessmemory,orRAM.Aspecialtypeofprimarystorage,calledread-onlymemory(ROM),cannotbealteredbytheprogrammer.ThecontentsofROMare“hard-wired”(designedintothelogicofthememorychip)bythemanufacturerandcanbe“readonly”.Whenyouturnonamicrocomputersystem,aprograminROMautomaticallyreadiesthecomputersystemforuse.ThentheROMprogramproducestheinitialdisplayscreenprompt.主存儲(chǔ)器也稱為隨機(jī)存取存儲(chǔ)器，或RAM。還有一種特殊的主存儲(chǔ)器，稱為只讀存儲(chǔ)器（ROM），這種存儲(chǔ)器不能被程序更改存放的內(nèi)容。ROM的內(nèi)容是被生產(chǎn)商通過硬件電路寫入的，并且不能被重寫。當(dāng)你啟動(dòng)計(jì)算機(jī)，ROM中的一個(gè)程序會(huì)自動(dòng)就緒等待計(jì)算機(jī)系統(tǒng)的調(diào)用，然后在顯示器中顯示開機(jī)提示。AvariationofROMisprogrammableread-onlymemory(PROM).PROMisROMintowhichyou,theuser,canload“read-only”programsanddata.OnceaprogramisloadedtoPROM,itisseldom,ifever,changed[4].However,ifyouneedtobeabletorevisethecontentsofPROM,thereisEPROM,erasablePROM.Beforeawriteoperation,allthestoragecellsmustbeerasedtothesameinitialstate.可編程只讀存儲(chǔ)器（PROM）是另一種ROM，它可以載入只讀的程序和數(shù)據(jù)，一旦載入，將不再改變。然而，若果你需要去修正PROM的內(nèi)容，可以使用可擦可編程只讀存儲(chǔ)器。EPROM在進(jìn)行一次寫操作之前，所有的存儲(chǔ)單元必須被還原為同一初始狀態(tài)。Amoreattractiveformofread-mostlymemoryiselectricallyerasableprogrammableread-onlymemory(EEPROM).Itcanbewrittenintoatanytime4/8

withouterasingpriorcontents;onlythebyteorbytesaddressedareupdated.一種更吸引人的可改寫只讀存儲(chǔ)器是電可擦除可編程只讀存儲(chǔ)器(EEPROM)。它可以在任何時(shí)候?qū)懭?，而且不?huì)擦除以前的內(nèi)容；只會(huì)更新被尋址的字節(jié)。TheEEPROMcombinestheadvantageofnonvolatilitywiththeflexibilityofbeingupdatableinplace[6],usingordinarybuscontrol,address,anddatalines.電可擦可編程存儲(chǔ)器把非易失性優(yōu)點(diǎn)和可更新、需要更新的地方的靈活性結(jié)合起來，修改時(shí)使用普通的總線控制線、地址線和數(shù)據(jù)線。Anotherformofsemiconductormemoryisflashmemory(sonamedbecauseofthespeed).FlashmemoryisintermediatebetweenEPROMandEEPROMinbothcostandfunctionality.LikeEEPROM,flashmemoryusesanelectricalerasingtechnology.Anentireflashmemorycanbeerasedinoneorafewseconds,whichismuchfasterthanEPROM.Inaddition,itispossibletoerasejustblocksofmemoryratherthananentirechip.However,flashmemorydoesnotprovidebyte-levelerasure[7].LikeEPROM,flashmemoryusesonlyonetransistorperbit,andsoachievesthehighdensityofEPROM.另一種半導(dǎo)體記憶體是閃存（意味著速度快）。閃存在性價(jià)比上處于EPROM和EEPROM之間，它使用電擦寫技術(shù)。整個(gè)閃存的內(nèi)容可以在一到幾秒內(nèi)被清除，這是遠(yuǎn)快于EPROM的。另外，它還可以對(duì)部分記憶塊而不是整個(gè)存儲(chǔ)器進(jìn)行清除。然而，閃存并不提供字節(jié)級(jí)的擦除。像EPROM，閃存只使用一個(gè)晶體管每比特，因此可以實(shí)現(xiàn)高密度的EPROM。CacheMemoryProgramanddataareloadedtoRAMfromsecondarystoragebecausethetimerequiredtoaccessaprograminstructionorpieceofdatafromRAMissignificantlylessthanfromsecondarystorage.ThousandsofinstructionsorpiecesofdatacanbeaccessedfromRAMinthetimeit5/8

wouldtaketoaccessasinglepieceofdatafromdiskstorage[8].RAMisessentiallyahigh-speedholdingareafordataandprograms.Infact,nothingreallyhappensinacomputersystemuntiltheprograminstructionsanddataaremovedtotheprocessor.Thistransferofinstructionsanddatatotheprocessorcanbetime-consuming,evenatmicrosecondspeeds.Tofacilitateanevenfastertransferofinstructionsanddatatotheprocessor,mostcomputersaredesignedwithcachememory.Cachememoryisemployedbycomputerdesignerstoincreasethecomputersystemthroughput(therateatwhichworkisperformed).程序和數(shù)據(jù)從輔助存儲(chǔ)器裝載到RAM中是因?yàn)閷?duì)RAM中的程序指令和數(shù)據(jù)的訪問時(shí)間要明顯的少于從輔助存儲(chǔ)器訪問。數(shù)以千條的指令和數(shù)據(jù)能被訪問而只需花費(fèi)從硬盤訪問一次數(shù)據(jù)的時(shí)間。RAM是數(shù)據(jù)和程序的上，計(jì)算機(jī)系統(tǒng)不會(huì)進(jìn)行任何操作直到程序指令被傳入處理器進(jìn)行執(zhí)行，這種指，即使傳輸速度已經(jīng)是以納秒來計(jì)算了。為了，大多數(shù)計(jì)算機(jī)設(shè)計(jì)使用高速緩存。計(jì)算機(jī)設(shè)計(jì)者使重要的高速存放區(qū)，事實(shí)令和數(shù)據(jù)的傳輸是需要花費(fèi)時(shí)間的能更快速的傳輸指令和數(shù)據(jù)用高速緩存來提高計(jì)算機(jī)系統(tǒng)的總處理能力（工作效率）。LikeRAM,cacheisahigh-speedholdingareaforprograminstructionsanddata.However,cachememoryusesSRAM(StaticRAM)technologythatisabout10timesfasterthanRAMandabout100timesmoreexpensive.WithonlyafractionofthecapacityofRAM,cachememoryholdsonlythoseinstructionsanddatathatarelikelytobeneedednextbytheprocessor.Twotypesofcachememoryappearwidelyincomputers.ThefirstisreferredtoasinternalcacheandisbuiltintotheCPUchip.Thesecond,externalcache,islocatedonchipsplacedclosetotheCPUchip.Acomputercanhaveseveraldifferentlevelsofcachememory.Level1cacheisvirtuallyalwaysbuiltintothechip.Level2cacheusedtobeexternalcachebutisnowtypicallyalsobuiltintotheCPUlikelevel1cache.6/8

和RAM一樣，高速緩存也是程序指令和數(shù)據(jù)的高速存儲(chǔ)區(qū)。然而，高速緩存使用靜態(tài)RAM技術(shù)，這種技術(shù)比RAM在速度上要高出10倍，價(jià)格上高出100倍。cache只保存內(nèi)存中那