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1、Introduction to Linux1.1 History1.1.1 UNIXInordertounderstandthepopularityofLinux,weneedtotravelbackintime,about30yearsago.Imaginecomputersasbigashouses,evenstadiums.Whilethesizesofthosecomputersposedsubstantialproblems,therewasonethingthatmadethisevenworse:everycomputerhadadifferentoperatingsystem.
2、Softwarewasalwayscustomizedtoserveaspecificpurpose,andsoftwareforonegivensystemdidntrunonanothersystem.Beingabletoworkwithonesystemdidntautomaticallymeanthatyoucouldworkwithanother.Itwasdifficult,bothfortheusersandthesystemadministrators.Computerswereextremelyexpensivethen,andsacrificeshadtobemadeev
3、enaftertheoriginalpurchasejusttogettheuserstounderstandhowtheyworked.ThetotalcostofITwasenormous.Technologicallytheworldwasnotquitethatadvanced,sotheyhadtolivewiththesizeforanotherdecade.In1969,ateamofdevelopersintheBellLabslaboratoriesstartedworkingonasolutionforthesoftwareproblem,toaddressthesecom
4、patibilityissues.Theydevelopedanewoperatingsystem,whichwassimpleandelegantwrittenintheCprogramminglanguageinsteadofinassemblycodeabletorecyclecode.TheBellLabsdevelopersnamedtheirprojectUNIX.Thecoderecyclingfeatureswereveryimportant.Untilthen,allcommerciallyavailablecomputersystemswerewritteninacodes
5、pecificallydevelopedforonesystem.UNIXontheotherhandneededonlyasmallpieceofthatspecialcode,whichisnowcommonlynamedthekernel.ThiskernelistheonlypieceofcodethatneedstobeadaptedforeveryspecificsystemandformsthebaseoftheUNIXsystem.Theoperatingsystemandallotherfunctionswerebuiltaroundthiskernelandwritteni
6、nahigherprogramminglanguage,C.ThislanguagewasespeciallydevelopedforcreatingtheUNIXsystem.Usingthisnewtechnique,itwasmucheasiertodevelopanoperatingsystemthatcouldrunonmanydifferenttypesofhardware.Thesoftwarevendorswerequicktoadapt,sincetheycouldselltentimesmoresoftwarealmosteffortlessly.Weirdnewsitua
7、tionscameinexistence:imagineforinstancecomputersfromdifferentvendorscommunicatinginthesamenetwork,orusersworkingondifferentsystemswithouttheneedforextraeducationtouseanothercomputer.UNIXdidagreatdealtohelpusersbecomecompatiblewithdifferentsystems.ThroughoutthenextcoupleofdecadesthedevelopmentofUNIXc
8、ontinued.MorethingsbecamepossibletodoandmorehardwareandsoftwarevendorsaddedsupportforUNIXtotheirproducts.UNIXwasinitiallyfoundonlyinverylargeenvironmentswithmainframesandminicomputers(notethataPCisamicrocomputer).Youhadtoworkatauniversity,forthegovernmentorforlargefinancialcorporationsinordertogetyo
9、urhandsonaUNIXsystem.Butsmallercomputerswerebeingdeveloped,andbytheendofthe80s,manypeoplehadhomecomputers.Bythattime,therewereseveralversionsofUNIXavailableforthePCarchitecture,butnoneofthemweretrulyfree.1.1.2 CurrentapplicationofLinuxsystemsTodayLinuxhasjoinedthedesktopmarket.Linuxdevelopersconcent
10、ratedonnetworkingandservicesinthebeginning,andofficeapplicationshavebeenthelastbarriertobetakendown.WedontliketoadmitthatMicrosoftisrulingthismarket,soplentyofalternativeshavebeenstartedoverthelastcoupleofyearstomakeLinuxanacceptablechoiceasaworkstation,providinganeasyuserinterfaceandMScompatibleoff
11、iceapplicationslikewordprocessors,spreadsheets,presentationsandthelike.Ontheserverside,Linuxiswell-knownasastableandreliableplatform,providingdatabaseandtradingservicesforcompanieslikeAmazon,thewell-knownonlinebookshop,USPostOffice,theGermanarmyandsuch.EspeciallyInternetprovidersandInternetservicepr
12、ovidershavegrownfondofLinuxasfirewall,proxy-andwebserver,andyouwillfindaLinuxboxwithinreachofeveryUNIXsystemadministratorwhoappreciatesacomfortablemanagementstation.ClustersofLinuxmachinesareusedinthecreationofmoviessuchasTitanic,Shrekandothers.Inpostoffices,theyarethenervecentersthatroutemailandinl
13、argesearchengine,clustersareusedtoperforminternetsearches.Theseareonlyafewofthethousandsofheavy-dutyjobsthatLinuxisperformingday-to-dayacrosstheworld.ItisalsoworthtonotethatmodernLinuxnotonlyrunsonworkstations,mid-andhigh-endservers,butalsoongadgetslikePDAs,mobiles,ashiploadofembeddedapplicationsandevenonexperimentalwristwatches.ThismakesLinuxtheonlyoperatingsystemintheworldcoveringsuchawiderangeofhardware.1.2Theuserinterface1.2.1 IsLinuxdifficult?WhetherLinuxisdifficulttolearndependsonthepersonyoureasking.
