《计算机英语实用教程》电子教案

Unit1ComputerBasics【教学目的】oLearnabouttheEnglishtermsofthebasicphysicalportionofthecomputer,includingCPU,monitor,motherboard,memory,RAM,ROM,mouse,keyboard,disk,USBandI/OportoImprovethestudents'abilitytounderstandthelonganddifficultsentencesinthetext.oMasterthekeylanguagepointsandgrammaticalstructuresinthetext.oconsolidatethetechnicaltermsandimportantprofessionalphrasesbydoingexercises.【教学重点难点】olmportanttechnicalterms:printedcircuitboard（印刷电路板），systembuses（系统总线），memorymodules（内存模块），plug-incards（即插即用卡），daughterboard（子板），peripheraldevice（外围设备），binarynumbersystem（二进制系统），rationalnumber（有理数），randomaccessmemory（随机存取存储器），read-onlymemory（只读存储器），diskdrive（磁盘驱动器），removabledisk（可移动磁盘），serialport（串口类型）,parallelport（并ロ）〇Abbreviation:CPU,RAM（FPM,EDO,SDRAM,DDR）,ROM,USB,SCSI;oDifficultsentences:Itisequippedwithsocketstowhichallprocessors,memorymodules,plug-incards,daughterboards,orperipheraldevicesareconnected....byutilizingthebinarynumbersystemitispossibletoproducearbitraryrationalnumbersandthroughcleverformattingallmannerofrepresentationsofpictures,sounds,andanimations.Adatastoragedeviceforwhichtheorderofaccesstodifferentlocationsdoesnotaffectthespeedofaccess,exceptforbursts.Notethoughthattherearedifferentcompetingformatusedforfloppies,sothatafloppywrittenbyonetypeofcomputermightnotdirectlyworkonanother,alsosometimescalled“diskette”.oReviewtheimportantpointsofessentialEnglishresponsibleforbeequippedwithbeidenticaltobesimilartoinconjunctionwithNotethoughthatbecapableofdoingsth.【教学步骤】StepOneReadandexplainTextAtothestudentsandaskthestudentstokeepinmindthefollowingprofessionalterms:printedcircuitboard（印刷电路板）BuyPrintedCircuitBoardAssembly（PCB）购买印刷电路板Wearelookingforsupplierinprintedcircuitboardassembly,我们正寻求印刷电路板的供应商。systembu§（系统总线）busthatconnectstheCPUtomainmemoryonthemotherboard,把CPU与母板上主存连接起来的总线Thesystembusisalsocalledthefrontsidebus,memorybus,localbus,orhostbus,系统总线也叫做前端总线（略作FSB）。memorymodule（内存模块,存储器模数）MemoryModulePicture20072007年的内存模块照片ThisarticleisanupdateofallthelatestmemorymodulefoundinthelatestIntelPentium,最新的Intel奔腾内存模块的更新文章plug-incards（即插即用卡）cf.plug-ins（插件）：Asoftwareplug-inisanadd-onforaprogramthataddsfunctionalitytoit.软件插件是一个给程序添加功能的附加软件。cf. Plugandplay即插即用PlugandPlay,sometimes,abbreviatedPnP,isacatchyphraseusedtodescribedevicesthatworkwithacomputersystemassoonastheyareconnected.Theuserdoesnothavetomanuallyinstalldriversforthedeviceoreventellthecomputerthatanewdevicehasbeenadded.Insteadthecomputerautomaticallyrecognizesthedevice,loadsnewdriversforthehardwareifneeded,andbeginstoworkwiththenewlyconnecteddevice.Forexample,ifyouconnectaPlug-and-PlaymousetotheUSBportonyourcomputer,itwillbegintoworkwithinafewsecondsofbeingpluggedin.Anonplug-and-playdevicewouldrequireyoutogothroughseveralstepsofinstallingdriversandsettingupthedevicebeforeitwouldwork.WhilePlugandPlayusuallyreferstocomputerperipheraldevices,suchaskeyboardsandmice,itcanalsobeusedtodescribeinternalhardware.Forexample,avideocardorharddrivcmaybeaPlugandPlaydevice,meaningthecomputerwillrecognizeitassoonasitisinstalled.Theonlydifferenceisthatinternalcomponentsusuallyrequirethecomputertobeturnedoff*whentheyareinstalled,whileexternaldevicescantypicallybeinstalledwhilethecomputerisrunning.daughterboard（子板）Smallprintedcircuitboardthatplugsintoamotherboardtogiveitnewcapabilities接入母板的小的印刷电路板,以增添新的功能。peripheraldevice（外围设备）Whataresomeexamplesofcomputerperipheraldevices?Answer:Acomputerperipheral,orperipheraldevice,isanexternalobjectthatprovidesinputandoutputforthecomputer.Somecommoninputdevicesinclude:keyboard,mouse,joystick,pentablet,MIDIkeyboard(musicalinstrumentdigitalinterface数码音响),scanner,digitalcamera,videocamera,microphone.Somecommonoutputdevicesinclude:monitor,projector,TVscreen,printer,plotter,speakers.Therearealsodevicesthatfunctionasbothinputandoutputdevices,suchas:externalharddrives,mediacardreaders,digitalcamcorders,digitalmixers,MIDIequipment.Whilethesearesomeofthemorecommonperipherals,therearemanyotherkindsaswell.Justrememberthatanyexternaldevicethatprovidesinputtothecomputerorreceivesoutputfromthecomputerisconsideredaperipheral.binarynumbersystem(二进制系统)Binaryisatwo-digit(Base-2)numericalsystem,whichcomputersusetostoredataandcomputefunctions.Thereasoncomputersusethebinarysystemisbecausedigitalswitchesinsidethecomputercanonlybesettoeitheronoroff,whicharerepresentedbya1or0.Thoughthebinarysystemconsistsofonlyonesandzeros,thetwodigitscanbeusedtorepresentanynumber.Forexample:Asingle0inbinaryrepresentszero.Asingle1represents(2A0)or1.represents(2A1)or2.represents(2A1+2A0)or3.100represents(2A2)or4.101represents(2A2+2A0)or5.110represents(2A2+2A1)or6.represents(2A2+2A1+2A0)or7.1000represents(2A3)or8,andsoon.rationalnumbers(有理数)Arationalnumberisanumberthatcanbeexpressedasafractionorratio(rational).Thenumeratorandthedenominatorofthefractionarebothintegers.Whenthefractionisdividedout,itbecomesaterminatingorrepeatingdecimal.(Therepeatingdecimalportionmaybeonenumberorabillionnumbers.)Cf.Anirrationalnumber(无理数)cannotbeexpressedasafraction.Irrationalnumberscannotberepresentedasterminatingorrepeatingdecimals.Irrationalnumbersarenon-terminating,non-repeatingdecimals.RAMrandomaccessmemory(随机存取存储器)RAMStandsfor"RandomAccessMemory,0andispronouncedlikethemalesheep.RAMismadeupofsmallmemorychipsthatareconnectedtothemotherboardofyourcomputer.Everytimeyouopenaprogram,itgetsloadedfromtheharddriveintotheRAM.ThisisbecausereadingdatafromtheRAMismuchfasterthanreadingdatafromtheharddrive.RunningprogramsfromtheRAMofthecomputerallowsthemtofunctionwithoutanylagtime.ThemoreRAMyourcomputerhas,themoredatacanbeloadedfromtheharddriveintotheRAM,whichcanhelpspeedupyourcomputer.Infact,addingRAMcanbemorebeneficialtoyourcomputer'sperformancethanupgradingtheCPU.ROMRead-OnlyMemory(只读存储器)Standsfor"Read-OnlyMemory."PleasedonotconfusethistermwithRAMoraharddrive,asmanypeoplealreadydo.ROMismemorycontaininghardwiredinstructionsthatthecomputeruseswhenitbootsup,beforethesystemsoftwareloads.InPCs,theinstructionsarereadfromasmallprogramintheROM,calledtheBIOS(BasicInput/OutputSystem).diskdrive(磁盘驱动器)Amachinethatreadsdatafromandwritesdataontoadisk.Adiskdriverotatesthediskveryfastandhasoneormoreheadsthatreadandwritedata.Therearedifferenttypesofdiskdrivesfordifferenttypesofdisks.Forexample,aharddiskdrive(HDD)readsandwritesharddisks,andafloppydrive(FDD)accessesfloppydisks.Amagneticdiskdrivereadsmagneticdisks,andanopticaldrivereadsopticaldisks.Diskdrivescanbeeitherinternal(housedwithinthecomputer)orexternal(housedinaseparateboxthatconnectstothecomputer).removabledisk(可移动磁盘)typeofdiskdrivesysteminwhichharddisksareenclosedinplasticormetalcartridgessothattheycanberemovedlikefloppydisks.Removablediskdrivescombinethebestaspectsofhardandfloppydisks.Theyarenearlyascapaciousandfastasharddisksandhavetheportabilityoffloppydisks.Theirbiggestdrawbackisthatthey'rerelativelyexpensive.serialport(串口类型)Aport,orinterface,thatcanbeusedforserialcommunication,inwhichonly1bitistransmittedatatime.Aserialportisageneral-purposeinterfacethatcanbeusedforalmostanytypeofdevice,includingmodems,mice,andprinters(althoughmostprintersareconnectedtoaparallelport).parallelport(并ロ)Aparallelinterfaceforconnectinganexternaldevicesuchasaprinter.Mostpersonalcomputershavebothaparallelportandatleastoneserialport.StepTwoHelpthestudentstoanalyzethefollowinglongdifficultsentences:Itisequippedwithsocketstowhichallprocessors,memorymodules,plug-incards,daughterboards,orperipheraldevicesareconnected.本句中,towhichallprocessors,memorymodules,plug-incards,daughterboards,orperipheraldevicesareconnected.是ー个由介词+关系代词引导的定语从句,修饰先行词sockets,表不的意思是allprocessors,memorymodules,plug-incards,daughterboards,orperipheraldevicesareconnectedtothesockets,beequippedwith的意思是“具有，装备有‘'；beconnectedto表示“与 连接

byutilizingthebinarynumbersystemitispossibletoproducearbitraryrationalnumbersandthroughcleverformattingallmannerofrepresentationsofpictures,sounds,andanimations.本句中,byutilizingthebinarynumbersystem和throughcleverformatting是介词短语做方式状语。it是形式主语,真正的主语是动词不定式短语toproducearbitraryrationalnumbers〇在allmannerofrepresentationsofpictures,sounds,andanimations刖省略Jitispossibletoproduce〇Adatastoragedeviceforwhichtheorderofaccesstodifferentlocationsdoesnotaffectthespeedofaccess,exceptforbursts.可以不用定语从句来表达同样的意思:Foradatastoragedevicetheorderofaccesstodifferentlocationsdoesnotaffectthespeedofaccess,exceptforbursts.对于数据存储设备来说除非有爆发性访问,访问顺序对访问速度没有影响。Notethoughthattherearedifferentcompetingformatusedforfloppies,sothatafloppywrittenbyonetypeofcomputermightnotdirectlyworkonanother,句中的though是副词,可以译成"但是"；note后面的that从句表达前因后果,后果用sothat引导。ComputerComponents:

HardwareMonitorbutton,31/2*diskdrive-drivethatedlovsyoutouse3.5disksAitovkeys-usedtohelplocatecertainspotsonthewindowordesktopCDROMdrive-drivethatallowsyoutouseCD*sCPU-CentralProcessingUnit:caseorhousingforinternaloperatingmechanismsFunction(F)keys-shortcutkeys(dependingonsoftware)Keypad-similartoatypewriterkeyboardMonitor-forviewingcomputeroperationsMouse-usedtohelplocateandactivatecertainthingsonthecorr^iuterNumericalkeypad-acalculator-typeareafornumericalenteringStartbuttons-buttonsusedtoturnthecon^uteronStepThreeReviewtheimportantidiomsofessentialEnglish

•responsibleforortoberesponsibleforsb/sth/doingsthtohavecontrolandauthorityoversomethingorsomeoneandthedutyoftakingcareofitorthem:控制,管理;负责Paulisdirectlyresponsiblefortheefficientrunningoftheoffice.Herdepartmentisresponsibleforoverseeingthecouncils.beresponsibletosb/sthtobecontrolledbysomeoneorsomething:被...控制レ监督InAustralia,thePrimeMinisterandtheCabinetofMinistersareresponsibletotheHouseofRepresentatives.beequippedwithequip(PROVIDE)vt.toprovideapersonoraplacewithobjectsthatarenecessaryforaparticularpurpose:配备It'sgoingtocost$4milliontoequipthehospital.Allthepoliceofficerswereequippedwithshieldstodefendthemselvesagainsttherioters.beidenticaltoidenticaladj.exactlythesame,orverysimilar:完全相同:非常相似I'vegotthreeidenticalbluesuits.Thetworoomswerevirtuallyidentical.Theinterestsofbothpartiesmaynotbeidentical,buttheydooverlapconsiderably.Thetestsareidenticaltothosecarriedoutlastyear.besimilartosimilaradj.lookingorbeingalmost,butnotexactly,thesame:类似(不完全ー样)MyfatherandIhavesimilarviewsonpolitics.IboughtsomenewshoeswhichareverysimilartoapairIhadbefore.Paulisverysimilarinappearancetohisbrother.inconjunctionwithconjunction(COMBINATION)n.[CorU](FORMALconjuncture)wheneventsorconditionscombineorhappentogether:合并;同时出现或发生Anunfortunateconjunctionofcircumstancesledtohisdownfall.Thereisateamofwritersworkinginconjunction(witheachother)onthebook.becapableofdoingsth.capableofsth/doingsthhavingtheability,powerorqualitiestobeabletodosomething:有能カ、力量或本领做某事OnlytheDemocraticPartyiscapableofrunningthecountry.Aforce10windiscapableofblowingtheroofsoffhouses.Whenshe'sdrunkshe'scapableofsaying(=likelytosay)awful,rudethings.Ithinkyourplaniscapableofbeing(=couldbe)improved.TheoppositeisincapableStepFourTextBTheterm"PC"isalsocommonlyusedtodescribean"IBM-compatible"personalcomputerincontradistinctiontoanAppleMacintoshcomputer.contradistinction：distinctionmadebycontrastingthedifferentqualitiesoftwothings.通过对照比较两样事情而发现的差别incontradistinctionto.•・与・..对照区另リ:The"Mac",knownforitsmoreintuitiveuserinterface,isassociatedwithgraphicdesignanddesktoppublishing.苹果机以更为直观的用户界面而闻名,它主要功能是图片设计和桌面印刷。Thecomputerkeyboardusesthesamekeyarrangementasthemechanicalandelectronictypewriterkeyboardsthatprecededthecomputer.precedevt.tobeorgobeforesomethingorsomeoneintimeorspace:（时间或空间）在…前面Boutros-GhaliprecededKofiAnnanastheSecretary-GeneraloftheUN.Itwouldbehelpfulifyouweretoprecedethereportwithanintroduction.Theoppositeisfollowalsovt.Payattentiontothedifferencebetween"precede"[ロロN留以①田♦式盘◎]and"proceed"[]proceed:vi.SLIGHTLYFORMALtocontinueasplanned:（偏向正式用语）按计划继续Hislawyershavedecidednottoproceedwiththecase.Pceedtodosthtodosomethingafteryouhavedonesomethingelse:先做件事,接着做另一件事情Shesatdownandproceededtotellmeaboutherskiingholiday.HUMOROUSHetoldmehewasonadietandthenproceededtoeataplatefulofchips!FORMALtomoveforwardortravelinaparticulardirection:（正式用语）前进或旅游PassengersforMadridshouldproceedtogate26forboarding.•Sincethattime,ithasbecomewhatmaybethemostubiquitousmachine-userinterfaceofalltime.如I果说成:Sincethattime,ithasbecomethemostubiquitousmachine-userinterfaceofalltime.»即themostubiquitousmachine-userinterfaceofalltime作表语,意思是“打那以来它成了始终ー贯的最为普遍使用的计算机用户界面。”文中的这句使用whatmaybethemost即what从句作表语,表达变得很有分寸“打那以來它可能成了始终ー贯的最为普遍使用的计算机用户界面。”附:PartsoftheComputerAcomputerismadeupofseveraldifferentparts.

Thecomputercaseisthemetalandplasticboxthatcontainsthemaincomponentsofthecomputer.Computercasescomeindifferentshapesandsizes.Adesktopcaseliesflatonadesk,andthemonitorusuallysitsontopofit.Atowercase,picturedbelow,istallandsitsnexttothemonitororonthefloor.Thefrontofthecaseusuallyhasanon/offswitchandtwoormoredrives.(You'lllearnmoreabouttheCDROMdriveand31/2"Floppydriveinlaterlessons.)Onthebackofthecomputercaseareconnectionportsmadetofitonlyonetypeofplug-indevice.Theportsincludemonitorcableport,keyboard/mouseports,networkcableport,microphone/speaker/auxiliaryinputportsandprinterport(SCSIorParallel).There'salsoaplaceforthepowercordplug.Themonitor,whichresemblesatelevision,iswherethecomputerdisplaystextandpictures.Thekeyboardletsyoutypeinformationintothecomputer.Itresemblesatypewriterkeyboard.PeripheryDeviPeripheryDevice【教学目的】oLearnabouttheEnglishtermsoftheperipherydevicesofthecomputer,includingdrive,bus,inkjetprinter,modem,PCI,plug&play,CD-ROM,Harddrive,vidio-card,printer,scanner,soundcard,oImprovethestudents9abilitytounderstandthelonganddifficultsentencesinTextAandTextB.oMasterthekeylanguagepointsandgrammaticalstructuresinthetext.〇consolidatethetechnicaltermsandimportantprofessionalphrasesbydoingexercises.【教学重点难点】olmportanttechnicalterms:zipdrive（压缩驱动器）,CD-ROMs（CD光盘）,DVD-ROMs（DVD光盘）,analogsignals（模拟信号）,digitalsignal（数字信号）,electronicfilingcabinet（电子档案柜）,bubblejet〇Abbreviation:CD-ROM,DVD-ROM,PCI,ISA,PCMCIA,CMOS,BIOS;oDifficultsentences:Amodemmodulatesoutgoingdigitalsignalsfromacomputerorotherdigitaldevicetoanalogsignalsoveraconventionaltelephonelineanddemodulatestheincominganalogsignalandconvertsittoadigitalsignalforthedigitaldevice（computer）.Mo-dem=modulate+demodulatePeripheralComponentInterconnect（PCI）isaninterconnectionsystembetweenamicroprocessorandattacheddevicesinwhichexpansionslotsarespacedcloselyforhighspeedoperation.oReviewtheimportantpointsofessentialEnglishbemeanttodosth.设计成做某事例句:Functionkeysaremeanttoperformuser-definedtasks.havesth.doneイ列可Adeviceforstoringand/orretrievingdata.Somedrives（suchasdiskdrives,zipdrives,andtapedrives）aretypicallycapableofhavingnewdatawrittentothem例句ー:Astandardthatgivescomputeruserstheabilitytoplugadeviceintoacomputerandhavethedevicerecognizedautomatically.【教学步骤】StepOneReadandexplainTextAtothestudentsandaskthestudentstokeepinmindthefollowingprofessionalterms:zipdrive（压缩驱动器）Ahigh-capacityfloppydiskdrivedevelopedbyIomegaCorporation.Zipdisksareslightlylargerthanconventionalfloppydisks,andabouttwiceasthick.Theycanhold100or250MBofdata.Becausethey'rerelativelyinexpensiveanddurable,theyhavebecomeapopularmediaforbackingupharddisksandfortransportinglargefiles.CD-ROM（CD光盘）Pronouncedsee-dee-rom.ShortforCompactDisc-Read-OnlyMemory,atypeofopticaldiskcapableofstoringlargeamountsofdata—upto1GB,althoughthemostcommonsizeis650MB（megabytes）.AsingleCD-ROMhasthestoragecapacityof700floppydisks,enoughmemorytostoreabout300,000textpages.CD-ROMsarestampedbythevendor,andoncestamped,theycannotbeerasedandfilledwithnewdata.ToreadaCD,youneedaCD-ROMplayer.AllCD-ROMsconformtoastandardsizeandformat,soyoucanloadanytypeofCD-ROMintoanyCD-ROMplayer.Inaddition,CD-ROMplayersarecapableofplayingaudioCDs,whichsharethesametechnology.CD-ROMsareparticularlywell-suitedtoinformationthatrequireslargestoragecapacity.Thisincludeslargesoftwareapplicationsthatsupportcolor,graphics,sound,andespeciallyvideo.DVD-ROM（DVD光盘）Anewtypeofread-onlycompactdiscthatcanholdaminimumof4.7GB（gigabytes）,enoughforafull-lengthmovie.TheDVD-ROMspecificationsupportsdiskswithcapacitiesoffrom4.7GBto17GBandaccessratesof600KBpsto1.3MBps.OneofthebestfeaturesofDVD-ROMdrivesisthattheyarebackward-compatiblewithCD-ROMs.ThismeansthatDVD-ROMplayerscanplayoldCD-ROMs,CD-Idisks,andvideoCDs,aswellasnewDVD-ROMs.NewerDVDplayerscanalsoreadCD-Rdisks.DVD-ROMsuseMPEG-2tocompressvideodata.analogu（模拟）&digital（数字）Alsospelledanalogue,describesadeviceorsystemthatrepresentschangingvaluesascontinuouslyvariablephysicalquantities.Atypicalanalogdeviceisaclockinwhichthehandsmovecontinuouslyaroundtheface.Suchaclockiscapableofindicatingeverypossibletimeofday.Incontrast,adigitalclockiscapableofrepresentingonlyafinitenumberoftimes（everytenthofasecond,forexample）.Ingeneral,humansexperiencetheworldanalogically.Vision,forexample,isananalogexperiencebecauseweperceiveinfinitelysmoothgradationsofshapesandcolors.Whenusedinreferencetodatastorageandtransmission,analogformatisthatinwhichinformationistransmittedbymodulatingacontinuoustransmissionsignal,suchasamplifyingasignafsstrengthorvaryingitsfrequencytoaddortakeawaydata.Forexample,telephonestakesoundvibrationsandturnthemintoelectricalvibrationsofthesameshapebeforetheyaretransmittedovertraditionaltelephonelines.Radiowavetransmissionsworkinthesameway.Computers,whichhandledataindigitalform,requiremodemstoturnsignalsfromdigitaltoanalogbeforetransmittingthosesignalsovercommunicationlinessuchastelephonelinesthatcarryonlyanalogsignals.Thesignalsareturnedbackintodigitalform（demodulated）atthereceivingendsothatthecomputercanprocessthedatainitsdigitalformat.bubblejetprinter（气泡喷墨打印机）气泡喷墨打印机是由佳能所开发的ー种喷墨印表技术,与一般压电式喷墨印表方式不同的是,气泡喷墨打印机使用特殊加热装置产生墨点。AtypeofinkjetprinterdevelopedbyCanon.Theprincipaldifferencebetweenbubblejetprintersandotherinkjetprintersisthatbubble-jetprintersusespecialheatingelementstopreparetheinkwhereasink-jetprintersusespiezoelectric[口か・曷・Q*图•叱/.ロ*切]（压电的）crystals.Atypeofprinterthatworksbysprayingionized ]（离子化的）inkatasheetofpaper.Magnetizedplates（磁化图版）intheink'spathdirecttheinkontothepaperinthedesiredshapes.InkJetprintersarecapableofproducinghighqualityprintapproachingthatproducedbylaserprinters.Atypicalinkjetprinterprovidesaresolution(分辨率)of300dotsperinch,althoughsomenewermodelsofferhigherresolutions.AdvantagesanddisadvantagesoftheinkprinterIngeneral,thepriceofinkjetprintersislowerthanthatoflaserprinters.However,theyarealsoconsiderablyslower.Anotherdrawbackofinkjetprintersisthattheyrequireaspecialtypeofinkthatisapttosmudgeon(弄脏)inexpensivecopierpaper.Becauseinkjetprintersrequiresmallermechanicalpartsthanlaserprinters,theyareespeciallypopularasportableprinters.Inaddition,colorinkjetprintersprovideaninexpensivewaytoprintfull-colordocuments.scanner:handheld,hopper-feedandflatbedSomescannersaresmallhand-helddevicesthatyoumoveacrossthepaper.Thesehand-heldscannersareoftencalledhalfscannersbecausetheycanonlyscan2to5inchesatatime.Hand-heldscannersareadequateforsmallpicturesandphotos,buttheyarcdifficulttouseifyouneedtoscananentirepageoftextorgraphics.Largerscannersincludemachinesintowhichyoucanfeedsheetsofpaper.Thesearccalledsheet-fedscanners.Sheet-fedscannersareexcellentforloosesheetsofpaper,buttheyareunabletohandlebound(装订的)documents.Asecondtypeoflargescanner,calledaflatbedscanner,islikeaphotocopymachine.Itconsistsofaboardonwhichyoulaybooks,magazines,andotherdocumentsthatyouwanttoscan.Overheadscanners(alsocalledcopyhoardscanners)looksomewhatlikeoverheadprojectors.Youplacedocumentsface-uponascanningbed,andasmalloverheadtowermovesacrossthepage.tapedriveAdevice,likeataperecorder,thatreadsdatafromandwritesitontoatape.Tapedriveshavedatacapacitiesofanywherefromafewhundredkilobytestoseveralgigabytes.Theirtransferspeedsalsovaryconsiderably.Fasttapedrivescantransferasmuchas20MB(megabytes)persecond.Thedisadvantageoftapedrivesisthattheyaresequential-accessdevices,whichmeansthattoreadanyparticularblockofdata,youneedtoreadalltheprecedingblocks.Thismakesthemmuchtooslowforgeneral-purposestorageoperations.However,theyaretheleastexpensivemediaformakingbackupsStepTwoHelpthestudentstoanalyzethefollowinglongdifficultsentences:Amodemmodulatesoutgoingdigitalsignalsfromacomputerorotherdigitaldevicetoanalogsignalsoveraconventionaltelephonelineanddemodulatestheincominganalogsignalandconvertsittoadigitalsignalforthedigitaldevice(computer).Mo-dem=modulate+demodulate这个长句解释了调制解调器的作用。Here“modulate“isavt.Andweoftensay"modulatesthtosth."Inthissentence"modulateoutgoingdigitalsignalsfromacomputerorotherdigitaldevicetoanalogsignalsoveraconventionaltelephoneline”meansinChinese:通过传统的电话线把从计算机或其他数字设备传出来的信号调制成模拟信号。同样后面的demodulate为“解调”,作者为了避免表达重复,加进ー个动词convertsth.to..,实际上当然也可以