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1、presentation1Information=Bit+ContextAsweallknow,eachprogramisasequenceofbits,eachwithavalueof0or1,and8-bit=1byte,eachbyterepresentssometextcharacterintheprogram.ButinmostmodernsystemsrepresenttextcharacterusingtheASCIIstandard,forexample,the"/n"correspondingtotheinte

2、gervalue10.AsfortheContext,Itwastheonlythingthatdistinguishesdifferentdataobjectswhenweviewthem.2Programsaretranslatedbyotherprograms.Ifwewantourprogramscanrunonthesystem,theindividualCstatementsmustbetranslatedbyotherprogramsintoasequenceoflow-level-machine-language

3、instruction.Soit'sanecessarythingthatwehavetodo.Justliketheoperatingsystemhavetothroughdevicedrivetocontralthehardwaredevices.Compilationsystem1.preprocessingphase2.compilationphase3.assemblyphase4.linkingphase3Understandhowcompilationsystemsworkcanmakeadifferenceofo

4、urprogram.optimizingprogramperformanceunderstandinglink-timeerrorAvoidingsecurityholesHowthe“helloprogram”runninginthehardwareHardwareOrganizationofasystemMadeby20121120178BUSESThebusescanbedividedinto3types,thedatabus,addressbusandcontrolbus.Thedatabusisusedfortrans

5、ferringdata.Theaddressbusisusedfortransferringdataaddress.Thecontrolbusisusedfortransferringthecontrolsignal.Runningthroughthesystemisacollectionofelectricalcalledbuses.I/ODevicesInput/outputdevicesarethesystem’sconnectiontotheexternalworld.TheexamplesystemhasfourI/O

6、devices:akeyboardandmouseforuserinput,adisplayforuseroutput,andadiskdrive(硬盘驱动器)forlong-termstorageofdataandprograms.VirtualMemoryBylijianqingWhat’svirtualmemory?WhenyourcomputerdoesnothaveenoughRAMtoholdaprogram,itmightusevirtualmemory.Thereareafewpoints tonoteabout

7、 thevirtualmemory1、Ideaofextendingmemory2、IsnottheRAM3、Nofakebutvirtual1、Onewaytoextendtheamountofmemoryaccessiblebyaprogramistousedisk2、Ineffect,RAMactslikecachefordisk.3、Theproblemwithdiskisthatit’sveryslowtoaccess.Diskiseasytogetmanyspacesforasmallcost.Butwestillw

8、anttoavoidaccessingthediskunnecessarily.Useofvirtualmemorya、virtualmemoryisoldconceptb、Peoplehavevirtualmemorybeforetheyhadcachec、v