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1、貓的工作原理（Howdoesacatwork）MODEMreviewWhatweoftencallModemisactuallytheabbreviationofModulator(modulator)andDemodulator(demodulator),andChineseiscalledmodem.Itwasalsocalled"thecat",affectionatelycalled"Modem"".Weknowthattheinformationinthecomputeriscomposedof"0"and"1"toformadigitalsi
2、gnal,whilethetelephonelinecanonlybeanalogsignals.Thus,whentwocomputerswanttotransmitdataoveratelephoneline,adeviceisneededfortheconversionofdigitalsignals.ThisdigitaltoanalogconverteristheModemwe'regoingtotalkabouthere.Whenthecomputertransmitsdata,itconvertsthedigitalsignalsintoc
3、orrespondinganalogsignalsbyModem.Thisprocessiscalledmodulation".Themodulatedsignalistransmittedthroughthetelephonecarriertoanothercomputerbefore,alsothroughthereceiverModemisresponsiblefortheanalogsignalintodigitalsignalcanberecognizedbycomputer,thisprocesswecall"demodulation".It
4、isthroughsucha"modulation"and"demodulation"ofthedigitaltoanalogconversionprocess,soastoachievetheremotecommunicationbetweentwocomputers.I.categoryofModemGenerallyspeaking,accordingtotheshapeandinstallationmethodsofModem,theycanberoughlydividedintothefollowingfourcategories:1,exte
5、rnalModemTheexternalModemisplacedoutsidethecabinetandconnectedwiththehostthroughserialcommunicationport.ThisModemisconvenient,smart,easytoinstall,flashingindicatorlight,easytomonitortheworkingstatusofModem.ButexternalModemrequirestheuseofadditionalpowerandcable.2,built-inModemThe
6、built-inModemneedstobedisassembledwheninstalling,andtheinterruptandtheCOMportaresetup,andtheinstallationistedious.TheModemtakesuptheslotonthemotherboard,butrequiresnoextrapowerandcable,andthepriceischeaperthantheexternalModem.3,PCMCIAplug-inModemPlugtypeModemismainlyusedfornotebo
7、okcomputer,smallvolume.Withmobilephones,mobileofficecanbeeasilyimplemented.4,racktypeModemRacktypeModemisequivalenttoasetofModemconcentratedinaboxorshell,andpoweredbyaunifiedpowersupply.RacktypeModemismainlyusedinthecentralcomputerroomofInternet/Intranet,telecommunicationbureau,c
8、ampusnetwork,financialinstitutionandsoon
