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1、北京大学计算机系PekingUniversityDepartmentofComputerScience&TechnologyFall19982.操作系统做什么？2.2硬件相关指实现代码中包含存储器的物治理地址，包含对设备接口寄存器和设备接口缓冲区的读写等等。包括：内外存物理存储空间大小的变化程序和数据在存储空间中物理位置的变化设备硬件数量的变化等等但不包括指令集的变化由于操作系统承担了上述工作，在其之上的各类程序就没有必要直接同硬件打交道了。硬件改变时，操作系统相应变化即可，其他的程序不用作出改变硬件相关还表现在有关硬件的状态必定带来对应代码的变化2.3与
2、应用无关是指这些工作是任何一个程序都需要的、最基本的工作它们具有共性，工作过程相同与具体应用无直接关系，即与用户所关心的应用目标无直接关系4.Whyareoperatingsystemsinteresting?4.1BringtogethermanyareasforComputerScience:–Programminglanguages.–Computerarchitecture/hardware.–Datastructures.–Algorithms.4.2AbstractionsOSisawizard,providingillusionofinfin
3、iteCPUs,infinitememory,singleworldwidecomputing,etc.4.3Large,complexsystems.•Performancevssimplicitytradeoff.•Hardwarevssoftware.5.Whatisanoperatingsystem?AndHowBigItisDefiningthetermOperatingSystem?Itisdifficult.SimpleOS:Whatifonlyoneapplicationatatime?Example:Veryearlycomputers,
4、earlyPCs,embeddedcontrollers(elevators,cars,…)Standarddevicedrivers,interrupthandles,mathlibraries,etc.MorecomplexOS:Whatifsharemachineamongmultipleapplication?Osmustmanageinteractionsamongdifferentapplicationsandvaryusers.Example:CPU,physicalmemory,I/Odevices:disks,printers,…OSma
5、nageallofthenandofferlibrariesofstandardservices.6.FunctionofOSApplication-----------------------<>VirtualMachineInterfaceOperatingSystem-----------------------<>PhysicalMachineInterfaceHardware7.1Disciplinearosehistoricallyfromasetofproblems.Insomesense,OSisasoftwareengineeringpr
6、oblems:Howdoyouconvertwhatthehardwaregivesyouintosomethingthattheapplicationprogrammerwant?ForanyOSarea,itbeginsbyaskingtwoquestions:What’sthehardwareinterface?(thephysicalreality)What’stheapplicationinterface(thenicerabstraction)7.2FunctionsofOSOSasCoordinator:Allowthings(multipl
7、eapplications/users)toworktogetherefficientlyandfairly.Protectusersfromeachother.OSasIllusiongenerator:Exportscleaner,higher-levelinterfacetohardware.Makehardwarelimitationgoaway.InfinitememoryandinfiniteprocessorsofferedbyOS.OSasStandardservices:Providestandardfacilitiesthatevery
8、oneneeds.OSasHistoryteacher:Learn
