电子信息类专业英语(第二版)李白萍.ppt

UnitEightAuxiliaryStorage,PassageACDandCD-ROMPassageBHardDisksandOpticalDisksPassageCIntroductiontoCD-ROM,PassageACDandCD-ROMAcompactdisc(CD)isalaser-read(alsotermed“opticallyread”)datastoragedeviceonwhichaudio,video,ortextualmaterialcanbestored.Althoughithasbeenusedprimarilytorecordstereophonicsoundandhassupplantedthelong-playingPHONOGRAPHrecordastheprincipalmediumformusicstorage,itoffersahugepotentialasthemediumforthestorageofmassiveamountsofmanytypesofinformation.1,Unliketheconventionalphonographrecord,theCDstoresinformationindigitalform.Stereophonic(two-channel)soundsignalsaredigitallysampledatarateof44,100timespersecondperchannel.Eachsampleisexpressedasabinarynumbervalueconsistingof16binarydigits,orbits.Thesampleddigitalvalues,alongwitherrorcorrectiondata,trackingcodes,andcueingdata,arerecordedonadigitaltape,whichisusedtomakecompression-moldedplasticdiscs12cm(4.72in)indiameter,eachcoveredbyathin,reflectivemetalliclayerandprotectedbyaclearplasticcoating.2Duringplayback,alow-poweredlaserbeamreadsthedigitaldatathroughthereflectiverearsurfaceofthedisk.1,TheCDimprovesoverconventionalrecordsandtaperecordingswithitsmoreuniformandaccuratefrequencyresponse,acompleteabsenceofbackgroundnoise,awiderdynamicrange(thedifferencebetweenthesoftestandloudestrecordablemusicalsounds),andlongerwearsincenothingmechanicaltouchesthesurfaceofthediscwhenitisplayed.Introducedin1992,theSonyMiniDiscmeasuresonly6.35cm(2.5in)indiameter,butitcanbeusedtorecordaswellasplayupto74minutesofmusic.Itssmallsizeismadepossiblebyasystemofdatareductionthatusespsycho-acousticprinciplestoeliminatedatathatisnotnormallyheardbythelistener-therebyreducingthedatadensitytoone-fifththatrequiredforconventionalCDs.Mini-Discscanbeusedonlywiththeirownrecorder-player.,AsecondimportantapplicationofCDtechnologyistheCD-ROM(CompactDiscReadOnlyMemory),atext/graphics/soundstoragemediumthatisaccessedthroughtheCD-ROMdriveinacomputer.ACD-ROMcanstoreinexcessof500megabytes(millionsofbytes)ofdataascomparedwithacomputersharddisk,whosemaximumstoragecapacityisabout200megabytes.(TheAcademicAmericanEncyclopediawasthefirstencyclopediatobemadeavailableasaCD-ROM,in1986).Newdatacompressiontechniques,whichcanfilteroutmassivequantitiesofunneededdata,haveexpandedCD-ROMcapacitiestoincludesoundandimageaswellastextstorage:in1993thefirstmovie(AHardDaysNight)wasrecordedonaCD-ROM.,TheInteractiveCompactDisc,orCD-I,isessentiallyaCD-ROMthatcanbeaccessedviaaCD-Iplayerattachedtoatelevisionset.Withanon-screencursorandahandheldcontrolpadtheusercanchoosehisorherownpaththroughagame,anarthistorytour,ora“HowTo”tutorialthatincludesCD-qualitysoundandthousandsoffull-colorimagesaswellastext.AmongthevariationoftheCD-IisthePhotoCD,whichrecordsstillphotosdigitally,fordisplayonaTVscreen.ImproveddatacompressiontechniquesforvideowilleventuallyallowmoviestorageonCD-Is,withaqualitycomparabletoboyslaser-recordedvideodiscs.,KEYWORDScompact紧密的compactdisk(简称CD)激光磁盘optically光学地，光地textual本文的；正文的stereophonic立体声的supplant代替，取代potential潜势(的)，潜力(的)coating涂层，层playback播放(录音带，唱片)uniform均匀的,psycho-acoustic心理(精神)听觉的；传音的encyclopedia百科全书cursor(计算机尺的)游标，指导(的)tutorial指导教师(的)，指导(的)variation变化，变量atarateof以的速率improveover在基础上改善indiameter直径inexcessof超过comparableto与可比,NOTES1Althoughithasbeenusedprimarilytorecordstereophonicsoundandhassupplantedthelong-playingPHONOGRAPHrecordastheprincipalmediumformusicstorage,itoffersahugepotentialasthemediumforthestorageofmassiveamountsofmanytypesofinformation.尽管CD最初用于记录立体声声音并且已经取代了留声机唱片而成为主要的音乐存储信息的媒体，但它作为能存储大量多种信息的媒体仍具有巨大的潜力。,2Thesampleddigitalvalues,alongwitherrorcorrectiondata,trackingcodes,andcueingdata,arerecordedonadigitaltape,whichisusedtomakecompression-moldedplasticdisc12cm(4.72in)indiameter,eachcoveredbyathin,reflectivemetalliclayerandprotectedbyaclearplasticcoating.采样的数据连同纠错数据、道代码和提示数据被记录在数字带上，数字带常常做成直径为12cm(4.72英寸)的模压型塑料片，每片都覆盖一层薄薄的反光金属，其外层有一层透明塑料保护层。along意为“连同”。errorcorrectiondata意为“纠错数据”。“whichis”为定语从句，修饰“aditgitaltape”。,EXERCISES1.Fillintheblanks.(1)Adisc(CD)isalaser-readdatastoragedevice.(2)TheCDstoresinformationinform.(3)Stereophonicsoundsignalsaredigitallyatarateof44,100timespersecondperchannel.(4)Newdatacompressiontechniquescanoutmassivequantitiesofunneededdata.(5)WhentheCDisplayed,nothingmechanicalitssurface.(6)TheCDimprovesoverconventionalrecordswithitsmoreandaccuratefrequencyresponse.,2.True/False.(1)TheCDstoresmoreinformationthantheconventionalrecord.()(2)TheCD-ROMisasecondimportantapplicationofCDtechnology.()(3)TheCDhasbeenusedmainlytorecordstereophonicsound.()(4)ACDcanonlystoresound.()(5)TheconventionalphonographworksinthesamemannerasaCD.()(6)ACD-ROMisaccessedthroughacomputerdrive.(),3.Fillintheblankswiththebestchoice.(1)Comparedwithotherkindsofrecords,theCD.a.isprotectedbyaclearplasticcoatingb.hasalessuniformfrequencyresponsec.isreadbyapowerfullaserbeamd.consistsof6binarydigitsorbits,(2)Whichofthefollowingistrue?a.In1992,thefirstmoviewasrecordedonaCD-ROM.b.Themaximumstoragecapacityofaharddiskisabout500megabytes.c.TheAcademicAmericanEncyclopediawasthefirstencyclopediatobemadeavailableasaCD-ROMin1986.d.TheusualCDis6.35cmindiameter.(3)WhichparagraphtellsoftheCDsworkingprinciples?a.2b.3c.4d.5,(4)Wecaninferthat.a.theconventionalrecordcanalsobeaccessedviaaCD-ROMdriveb.theconventionalrecordhasaslongasaservicelifeastheCDc.theCDismuchcheaperthantheconventionaloned.thePhotoCDrecordsphotosindigitalform(5)Thepassageisprobablytakenfrom.a.atextbookb.acomputermanualc.anencyclopediad.apopularmagazine,4.TranslatethefollowingsentencesintoChinese.(1)Acompactdisc(CD)isalaser-read(alsotermed“opticallyread”)datastoragedeviceonwhichaudio,video,ortextualmaterialcanbestored.Althoughithasbeenusedprimarilytorecordstereophonicsoundandhassupplantedthelong-playingPHONOGRAPHrecordastheprincipalmediumformusicstorage,itoffersahugepotentialasthemediumforthestorageofmassiveamountsofmanytypesofinformation.(2)TheCDimprovesoverconventionalrecordsandtaperecordingswithitsmoreuniformandaccuratefrequencyresponse,acompleteabsenceofbackgroundnoise,awiderdynamicrange(thedifferencebetweenthesoftestandloudestrecordablemusicalsounds)andlongerwearsincenothingmechanicaltouchesthesurfaceofthediscwhenitisplayed.,PassageBHardDisksandOpticalDisksTheharddiskdriveprovidesincreasedstoragecapabilitiesandfasteraccess.HarddisksweredevelopedbyIBMin1973.Theearlyoneswereextremelyexpensive;however,withmassproductionofthepersonalcomputer,aharddiskdriveisnowavailableforaslittleas$200,anditisincorporatedintothecomputersystem.Afixed,harddiskusuallyhasoneormorediskplatterscoatedwithametaloxidesubstancethatallowsinformationtobemagneticallystoredonit.Thisstoragesystemincludesthedisk,aread/writeheadassembly,andtheconnectionsbetweenthedriveandthecomputer.,Atfirst,thesediskdrivesused14inchdisks,butnowtheyuse51/4inch,31/2inch,21/2inch,and14/5inchdiameters.Incontrasttothefloppydiskdrive,harddiskdrivesholdfrom80megabytestogigabytesandterabytesofinformation.Whenpurchasingaharddisk,considerstoragecapacityandseektime,ameasureofaharddisksaccessspeed.Thesmallerthenumbers,thefasterthedisk.Inthepast,65millisecondswasthestandardaccesstime,buttodaythestandardislessthan7milliseconds.,HowIsDataStoredonaHardDisk?Storingdataonharddisksissimilartostoringdataondiskettes.Inordertoreadorwritedataonthesurfaceofthespinningdiskplatter,thediskdrivesaredesignedwithaccessarms,oractuators.Theaccessarms,oractuators,containoneormoreread/writeheadsperdisksurface.Asthediskrotatesatahighrateofspeed,usually3,600revolutionperminute,theread/writeheadsmoveacrossitssurface.Theseread/writeheadsfloatonacushionofairanddonotactuallytouchthesurfaceofthedisk.Thedistancebetweentheheadandthesurfacevariesfromapproximatelytentotwentymillionthsofaninch.Ifsomeformofcontaminationisintroducedorifthealignmentoftheread/writeheadsisalteredbysomethingaccidentallyjarringthecomputer,thediskheadcancollideanddamagethedisksurface,causingalossofdata.Thiseventisknownasaheadcrash.Becauseofthetimeneededtorepairthediskandtoreconstructthedatathatwaslost,headcrashescanbeextremelycostlytousersintermsofbothtimeandmoney.,HowIsDataPhysicalOrganizedonaHardDisk?Dependingonthetypeofdiskdrive,dataisphysicallyorganizedinoneoftwoways.Onewayisthesectormethodandtheotheristhecylindermethod.Thesectormethodforphysicallyorganizingdataondisksdivideseachtrackonthedisksurfaceintoindividualstorageareascalledsectors.Eachsectorscancontainaspecifiednumberofbytes.Dataisreferencedbyindicatingthesurface,track,andsectorwherethedataisstored.,Withthecylindermethod,alltracksofthesamenumberoneachrecordingsurfaceareconsideredpartofthesamecylinder.Forexample,thefifthtrackonallsurfaceswouldbeconsideredpartofcylinderfive.Alltwentiethtrackswouldbepartofcylindertwentyandsoon.Whenthecomputerrequestsdatafromadiskusingthecylindermethod,itmustspecifythecylinder,recordingsurface,andrecordnumber.Becausetheaccessarmscontainingtheread/writeheadsallmovetogether,theyarealwaysoverthesametrackonallsurfaces.Thus,usingthecylindermethodtorecorddatadownthedisksurfacesreducesthemovementoftheread/writeheadduringbothreadingandwritingofdata.,AdvantageofUsingaHardDiskonaPersonalComputerAharddriveonapersonalcomputerprovidesmanyadvantagesforusers.Becauseofitslargestoragecapacity,aharddiskcanstoremanysoftwareapplicationprogramsanddatafiles.Whenauserwantstorunaparticularapplicationoraccessaparticulardatafileonaharddisk,itisalwaysavailable.Theuserdoesnothavetofindtheappropriatedisketteandinsertitintothedrive.Inaddition,thefasteraccesstimeofaharddiskreducesthetimeneededtoloadprogramsandaccessdata.Enormousquantitiesofinformationarestoredonopticaldisksbyusingalasertoburnmicroscopicholesonthesurfaceofahardplasticdisk.Alowerpowerlaserreadsthediskbyreflectinglightoffthedisksurface.Thereflectedlightisconvertedintoaseriesofbitsthatthecomputercanprocess.,Afull-size,14-inchopticaldiskcanstore6.8billionbytesofinformation.Thesmallerdisks,justunderfiveinchesindiameter,canstoreover800millioncharacters,orapproximately1,100timesthedatathatcanbestoredonastandarddensity31/2inchdiskette.Thatsenoughspacetostoreapproximately400,000pagesoftypeddata.ThesmalleropticaldisksarecalledCD-ROM,anacronymforcompactdiskread-onlymemory.TheyusethesamelasertechnologythatisusedfortheCD-ROMdisksthathavebecomepopularforrecordedmusic.,Mostopticaldisksareprerecordedandcannotbemodifiedbytheuser.Thesedisksareusedforapplicationssuchasanautopartscatalogwheretheinformationischangedonlyoccasionally,suchasonceayear,andanewupdatedopticaldiskiscreated.2Opticaldiskdevicesthatprovideforone-timerecordingarecalledWORMdevices,anacronymforwriteonce,readmany.Erasableopticaldiskdrivesarejuststartingtobeused.Themostcommonerasableopticaldrivesusemagneto-opticaltechnology,inwhichamagneticfieldchangesthepolarityofaspotonthediskthathasbeenheatedbyalaser.Becauseoftheirtremendousstoragecapacities,entirecatalogsorreferencematerialscanbestoredonasingleopticaldisk.Somepeoplepredictthatdiskswillsomedayreplacedatanowstoredonfilmsuchasmicrofiche.,KEYWORDSauxiliarystorage(alsocalledsecondarystorage)辅助存储器diskettes(alsocalledfloppydisk)软盘harddisks硬盘opticaldisks光盘track磁道sector扇区cylinder柱面,NOTES1Theseread/writeheadsfloatonacushionofairanddonotactuallytouchthesurfaceofthedisk.这些读/写头在高压气流上漂浮，移动时并不与盘片表面真正接触。cushion也可译为“气垫”。2Thesedisksareusedforapplicationssuchasanautopartscatalogwheretheinformationischangedonlyoccasionally,suchasonceayear,andanewupdatedopticaldiskiscreated.这种光盘用于信息量大，不需要经常更改信息内容的场合。比如，一个汽车零件目录，其中的信息是经过一段时间(如一年)才更改一次，需要更改时再制作一个新的光盘就可以了。autopartscatalog可译为“汽车零件目录”。,EXERCISES1.Fillintheblankswiththebestchoice.(1)Theprogramsanddatathatarenotcurrentlybeingprocessedbythecomputerarecommonlystoredon.a.RAMb.EPROMc.auxiliarystoraged.ROM(2)Mostauxiliarystoragedevicesare.a.volatileb.difficulttoreadc.difficulttowrited.non-volatile(3)Auxiliarystoragedevicescanbeusedasdevices.a.inputb.outputc.storaged.allofabove,(4)isusedasaprincipalauxiliarystoragemediumforpersonalcomputers.a.CD-ROMb.Diskettec.Taped.Corememory(5)Thetimerequiredtoretrievedatafromadisketteandplaceitinmainmemoryiscalledthe.a.seektimeb.accesstimec.settlingtimed.datatransferrate(6)Thetimeusedtopositiontheread/writeheadoverthepropertrackiscalled.a.seektimeb.accesstimec.rotationaldelayd.settlingtime(7)Thetimeittakesforthesectorcontainingthedatatorotateundertheread/writeheadiscalled.a.seektimeb.accesstimec.settlingtimed.rotationaldelay,(8)Thetimerequiredfortheread/writeheadtobeplacedincontactwiththediskiscalled.a.datatransferrateb.seektimec.settlingtimed.accesstime(9)Dataistransferredbetweenmainmemoryandthedisksurfaceaatatime.a.trackb.sectorc.cylinderd.word(10)Theformattingprocessdefinesonthesurfacesofadiskette.a.tracksb.sectorsc.cylindersd.allofabove,PassageCIntroductiontoCD-ROMSincecompactdiscsstoreaudioinadigitalformattheyaresuitableforstoringotherdigitalinformation.In1984,PhillipsandSonyreleasedtheCompactDiscReadOnlyMemory(CD-ROM)specification,knownastheYellowBook.ThisdefinesthenecessaryadditionstotheRedBookforthestorageofcomputerdata.ThephysicalparametersofCD-ROMsareidenticaltothosedefinedintheRedBook.Theuseofthedataitcontainsisdifferent.WhileaudioCDscanbeplayedatonlyonespeed,CD-ROMdrivesexistwitharangeofspeedoptionsfromnormal(1x)tofourtimesnormalspeed(4x)and,now,52x.Asthespeedincreasestheaccesstimealsodecreases.,CD-ROMdiscsdifferfromCDaudiodiscsintwoimportantways.ThedataonaCD-ROMdiscaredividedintosectorswhichcontainbothuserdataandotherdataforcontroland(additional)errorprotection.ThedataonaCD-ROMarecontainedinfiles.AllCD-ROMsthereforeneedafilesystemtoenablethecomputertoaccesstherequiredfil