操作系统基础(第一章).ppt

操作系统设计与实现,主讲教师：徐战亚Email：zhanyaxu,指定教材,TheMINIXBook:“OperatingSystems:设计与实现”byAndrewTanenbaumandAlbertWoodhull,第二版.中文版：操作系统设计与实现（第二版）（电子工业出版社）嵌入式实时操作系统uCOS-II邵贝贝,需要具备的一些技能,编程语言:-C(C+)and汇编-数据结构0751呢但在此要说明一下，只是运行chmod的用户对此文件有w的权限才能重新设置文件权限。root可设置任何文件的权限.,Howtousemount,/mnt/floppy/mnt/cdromitisthedefaultdirectoryformountfloppyandcd-rom,itsfolder,andinsomelinuxsystems,thedefaultisempty,wecanaddfilesthere,butoncetherealdriverismounted,theoriginalfileswontbevisit,whenwechangeourfloppy,wehavetounmountthedisk,andremountthenewone.,文件的另类存在-设备文件,Inlinux,inordertomaketheI/Odeviceslooksmorelikefile,thespecialappeared.blockspecialfilediskcharacterspecialfileprinter,modem由于设备文件就代表了整个设备，就可以使用标准命令直接操作设备文件，从而直接访问硬件设备。利用这种方式，能完成很多有用的工作，但是这种方式也非常危险，例如对硬盘设备文件的操作失误会破坏整个硬盘的数据。幸好大部分直接访问设备的操作都为读取相应数据的操作，而不需要写入磁盘设备。当某个设备不可使用，则其对应的设备文件也不能正常访问，因此直接访问设备文件可以判断对应的设备是否真正正常。例如，判断连接到第一个串口，ttyd0上的鼠标是否正常工作，使用命令“cat/dev/ttyd0”来查看ttyd0上的输入数据，如果连接的有鼠标且工作正常，那么在移动鼠标的同时屏幕上就会显示出接收到的杂乱数据。如果没有反应，说明鼠标工作不正确。但这也可能是其他程序接管了这个设备.,文件的另类存在-管道文件Pipe,连接两个进程的虚拟文件,More:sometimes,theoutputofaprocessisacommonfile,sometimestheoutputisapipefile,wehavetousespecialsystemcalltodistinguishthem.,概念三：Shell,Editors、compilersassemblerslinkersinterpretersnotbelongtoOS,butfromthem,wecouldfamiliarwiththeOS.#/bin/shShell-acommandinterpretermanycommandthere,wewillfamiliarwiththemlater.Eg:ShXXX.shchangeitsproperty,andrunit,概念四：系统调用SystemCall,系统调用是操作系统提供给软件开发人员的唯一接口，开发人员可利用它使用系统功能。OS核心中都有一组实现系统功能的过程（子程序），系统调用就是对上述过程的调用。Forcomputersdifferenttype,thesystemcallaredifferent,andalmostallthebasicfunctionsareprogrammedbyassemblerlanguage.,Eg:CallreadfunctioninClanguage.count=read(file,buffer,nbytes);file:thefileweareoperateon;buffer:thebufferareaweareusing;nbytes:thebyteswewillread.(sometimes,thecountmaylessthennbytes)SystemCallofMinix-SixParts.Processmanagement.Signals.Filemanagement.Directory(3)*Asetofserviceprocedurescarryoutthesystemcalls;(2)*Asetofutilityprocedureshelptheserviceprocedures.,1.52LayeredSystems,Comparewiththeprepic,itlookslikeasimplifiedlayeredsystem,eachlayerservesforitsupperlevel,andifweaddmoredetailsthere,wewillgottheTHE.DijkstraandhisstudentsdesignedthesystemforElectrologicaX8-1968TheTHEisofsixlayers,eachlayerchargeofitswork,andserveforupperlayers.Wheninthislayer,weneedntcaremoredetailofotherlayers.,LayersofTHE,Layer0:providedthebasicmultiprogrammingoftheCPU;Layer1:didthememorymanagement;Layer2:handledcommunicationbetweeneachprocessandoperationconsole;Layer3:Input/OutputmanagementLayer4:UserprogramsLayer5:TheoperatorBut!Alltheselayersjustthedesignaid,infact,allthepartsareultimatelylinkedtogetherintoasingleobjectprogram.,InMULTICSLayersisreplacedbyconcentricrings,andeachringdiddifferenttotheothers,soitismorepopular,andsystemcallhasmorestrictcheckontheirparameters.,1.53VirtualMachine,VirtualMachineinJava:Todifferentmachine,differentOperatingSystemOriginalVirtualMachine:(toanyuser,itlookslikewokingforhimself)Time-SharingMachineIBMOS/360,CP/CMSVM/370Thecharactersoftime-sharingOS:1.multiprogramming2.anextendmachinewithamoreconvenientinterfacethanthebarehardware,ThekernelofthisOS,wecalleditvirtualmachinemonitor,runsonabaremachineanddoesmulti-programming,itprovidesmanyvirtualmachines,andeachofthemisanexactcopyofabaremachine,includekernel/usermode、I/O、interruptsJustlikethepic:,Virtualmachinesonaserver,thedifferentvirtualmachinemayrunningthedifferentOS,whilethesingle-user,interactivesystemcalledCMS(ConversationalMonitorSystem).,VM/370BAREMACHINE,I/Oinstruction,Trap,Systemcall,Trap,Applications,TherunningofMS-DOSonWindows:Pentium(32bits):itprovidedavirtual8086modeMS-DOS(16bits)