中英文翻譯--網(wǎng)絡(luò).doc

TheNetWorksBirthoftheNetTheInternethashadarelativelybrief,butexplosivehistorysofar.Itgrewoutofanexperimentbeguninthe1960sbytheU.S.DepartmentofDefense.TheDoDwantedtocreateacomputernetworkthatwouldcontinuetofunctionintheeventofadisaster,suchasanuclearwar.Ifpartofthenetworkweredamagedordestroyed,therestofthesystemstillhadtowork.ThatnetworkwasARPANET,whichlinkedU.S.scientificandacademicresearchers.ItwastheforerunneroftodaysInternet.In1985,theNationalScienceFoundation(NSF)createdNSFNET,aseriesofnetworksforresearchandeducationcommunication.BasedonARPANETprotocols,theNSFNETcreatedanationalbackboneservice,providedfreetoanyU.S.researchandeducationalinstitution.Atthesametime,regionalnetworkswerecreatedtolinkindividualinstitutionswiththenationalbackboneservice.NSFNETgrewrapidlyaspeoplediscovereditspotential,andasnewsoftwareapplicationswerecreatedtomakeaccesseasier.CorporationssuchasSprintandMCIbegantobuildtheirownnetworks,whichtheylinkedtoNSFNET.AscommercialfirmsandotherregionalnetworkprovidershavetakenovertheoperationofthemajorInternetarteries,NSFhaswithdrawnfromthebackbonebusiness.NSFalsocoordinatedaservicecalledInterNIC,whichregisteredalladdressesontheInternetsothatdatacouldberoutedtotherightsystem.ThisservicehasnowbeentakenoverbyNetworkSolutions,Inc.,incooperationwithNSF.HowtheWebWorksTheWorldWideWeb,thegraphicalportionoftheInternet,isthemostpopularpartoftheInternetbyfar.OnceyouspendtimeontheWeb,youwillbegintofeellikethereisnolimittowhatyoucandiscover.TheWeballowsrichanddiversecommunicationbydisplayingtext,graphics,animation,photos,soundandvideo.Sojustwhatisthismiraculouscreation?TheWebphysicallyconsistsofyourpersonalcomputer,webbrowsersoftware,aconnectiontoanInternetserviceprovider,computerscalledserversthathostdigitaldataandroutersandswitchestodirecttheflowofinformation.TheWebisknownasaclient-serversystem.Yourcomputeristheclient；theremotecomputersthatstoreelectronicfilesaretheservers.Hereshowitworks:LetssayyouwanttopayavisittothetheLouvremuseumwebsite.FirstyouentertheaddressorURLofthewebsiteinyourwebbrowser(moreaboutthisshortly).ThenyourbrowserrequeststhewebpagefromthewebserverthathoststheLouvressite.TheLouvresserversendsthedataovertheInternettoyourcomputer.Yourwebbrowserinterpretsthedata,displayingitonyourcomputerscreen.TheLouvreswebsitealsohaslinkstothesitesofothermuseums,suchastheVaticanMuseum.Whenyouclickyourmouseonalink,youaccessthewebserverfortheVaticanMuseum.ThegluethatholdstheWebtogetheriscalledhypertextandhyperlinks.ThisfeatureallowelectronicfilesontheWebtobelinkedsoyoucaneasilyjumpbetweenthem.OntheWeb,younavigatethroughpagesofinformationbasedonwhatinterestsyouatthatparticularmoment,commonlyknownasbrowsingorsurfingtheNet.ToaccesstheWebyouneedwebbrowsersoftware,suchasNetscapeNavigatororMicrosoftInternetExplorer.HowdoesyourwebbrowserdistinguishbetweenwebpagesandotherfilesontheInternet?WebpagesarewritteninacomputerlanguagecalledHypertextMarkupLanguageorHTML.SomeWebHistoryTheWorldWideWeb(WWW)wasoriginallydevelopedin1990atCERN,theEuropeanLaboratoryforParticlePhysics.ItisnowmanagedbyTheWorldWideWebConsortium,alsoknownastheWorldWideWebInitiative.TheWWWConsortiumisfundedbyalargenumberofcorporatemembers,includingAT&T,AdobeSystems,Inc.,MicrosoftCorporationandSunMicrosystems,Inc.ItspurposeistopromotethegrowthoftheWebbydevelopingtechnicalspecificationsandreferencesoftwarethatwillbefreelyavailabletoeveryone.TheConsortiumisrunbyMITwithINRIA(TheFrenchNationalInstituteforResearchinComputerScience)actingasEuropeanhost,incollaborationwithCERN.TheNationalCenterforSupercomputingApplications(NCSA)attheUniversityofIllinoisatUrbana-Champaign,wasinstrumentalinthedevelopmentofearlygraphicalsoftwareutilizingtheWorldWideWebfeaturescreatedbyCERN.NCSAfocusesonimprovingtheproductivityofresearchersbyprovidingsoftwareforscientificmodeling,analysis,andvisualization.TheWorldWideWebwasanobviouswaytofulfillthatmission.NCSAMosaic,oneoftheearliestwebbrowsers,wasdistributedfreetothepublic.ItleddirectlytothephenomenalgrowthoftheWorldWideWeb.UnderstandingWebAddressesYoucanthinkoftheWorldWideWebasanetworkofelectronicfilesstoredoncomputersallaroundtheworld.Hypertextlinkstheseresourcestogether.UniformResourceLocatorsorURLsaretheaddressesusedtolocatethesefiles.TheinformationcontainedinaURLgivesyoutheabilitytojumpfromonewebpagetoanotherwithjustaclickofyourmouse.WhenyoutypeaURLintoyourbrowserorclickonahypertextlink,yourbrowserissendingarequesttoaremotecomputertodownloadafile.WhatdoesatypicalURLlooklike?Herearesomeexamples:/Thehomepageforstudyenglish./pub/AdirectoryoffilesatMIT*availablefordownloading.news:rec.gardens.rosesAnewsgrouponrosegardening.ThefirstpartofaURL(beforethetwoslashes*tellsyouthetypeofresourceormethodofaccessatthataddress.Forexample:http-ahypertextdocumentordirectorygopher-agopherdocumentormenuftp-afileavailablefordownloadingoradirectoryofsuchfilesnews-anewsgrouptelnet-acomputersystemthatyoucanlogintoovertheInternetWAIS*-adatabaseordocumentinaWideAreaInformationSearchdatabasefile-afilelocatedonalocaldrive(yourharddrive)Thesecondpartistypicallytheaddressofthecomputerwherethedataorserviceislocated.Additionalpartsmayspecifythenamesoffiles,theporttoconnectto,orthetexttosearchforinadatabase.YoucanentertheURLofasitebytypingitintotheLocationbarofyourwebbrowser,justunderthetoolbar.MostbrowsersrecordURLsthatyouwanttouseagain,byaddingthemtoaspecialmenu.InNetscapeNavigator,itscalledBookmarks.InMicrosoftExplorer,itscalledFavorites.OnceyouaddaURLtoyourlist,youcanreturntothatwebpagesimplybyclickingonthenameinyourlist,insteadofretypingtheentireURL.MostoftheURLsyouwillbeusingstartwithhttpwhichstandsforHypertextTransferProtocol*.httpisthemethodbywhichHTMLfilesaretransferredovertheWeb.HerearesomeotherimportantthingstoknowaboutURLs:AURLusuallyhasnospaces.AURLalwaysusesforwardslashes(/).IfyouenteraURLincorrectly,yourbrowserwillnotbeabletolocatethesiteorresourceyouwant.Shouldyougetanerrormessageorthewrongsite,makesureyoutypedtheaddresscorrectly.YoucanfindtheURLbehindanylinkbypassingyourmousecursoroverthelink.ThepointerwillturnintoahandandtheURLwillappearinthebrowsersstatusbar,usuallylocatedatthebottomofyourscreen.DomainNamesWhenyouthinkoftheInternet,.JustwhatdothosethreelettersattheendofaWorldWideWebaddressmean?EverycomputerthathostsdataontheInternethasauniquenumericaladdress.Forexample,thenumericaladdressfortheWhiteHouseis00.Butsincefewpeoplewanttorememberlongstringsofnumbers,theDomainNameSystem(DNS)*wasdeveloped.DNS,acriti