《操作系统概念》第六版作业解答1

Chapter11.1Whatarethethreemainpurposesofanoperatingsystem?环境提供者，为计算机用户提供一个环境，使得能够在计算机硬件上方便、高效的执行程序资源分配者，为解决问题按需分配计算机的资源，资源分配需尽可能公平、高效控制程序监控用户程序的执行，防止出错和对计算机的不正当使用管理I/O设备的运行和控制1-cont.1.3Whatisthemainadvantageofmultiprogramming?高效地使用CPU，通过重叠来自不同用户对CPU和I/O设备的需求增加CPU的利用，设法让CPU执行有意义的指令1-cont.1.5Inamultiprogrammingandtime-sharingenvironment,severaluserssharethesystemsimultaneously.Thissituationcanresultinvarioussecurityproblems.a.Whataretwosuchproblems?b.Canweensurethesamedegreeofsecurityinatime-sharedmachineaswehaveinadedicatedmachine?Explainyouranswer.用户之间互相偷数据、代码对系统资源使用的记账信息1-cont.1.6Definetheessentialpropertiesofthefollowingtypesofoperatingsystems:a.Batch相似需求的Job分批、成组的在计算机上执行，Job由操作员或自动Job程序装置装载；可以通过采用buffering,off-lineoperation,spooling,multiprogramming等技术使CPU和I/O不停忙来提高性能批处理适合于需要极少用户交互的Job。b.Interactive由许多短交易组成，下一次交易的结果可能不可预知需要响应时间短1-cont.1.6Definetheessentialpropertiesofthefollowingtypesofoperatingsystems:c.Timesharing使用CPU调度和多道程序提供对系统的经济交互式使用，CPU快速地在用户之间切换一般从终端读取控制，输出立即打印到屏幕d.Realtime在专门系统中使用，从传感器读取信息，必须在规定时间内作出响应以确保正确的执行1-cont.1.6Definetheessentialpropertiesofthefollowingtypesofoperatingsystems:e.Network在通用OS上添加联网、通信功能远程过程调用文件共享f.Distributed具有联网、通信功能提供远程过程调用提供多处理机的统一调度调度统一的存储管理分布式文件系统1-cont.1.9Describethedifferencesbetweensymmetricandasymmetricmultiprocessing.Whatarethreeadvantagesandonedisadvantageofmultiprocessorsystems?Symmetricmultiprocessing中所有处理器同等对待，I/O可以在任意CPU上处理。Asymmetricmultiprocessing具有一个主CPU和多个从CPU，主CPU将任务分派到从CPU，I/O通常只能由主CPU处理。多处理机系统的优点比多个计算机系统可能更省钱（同样CPU个数）执行程序更快可靠性更高缺点：软硬件更复杂Chapter22.2Howdoesthedistinctionbetweenmonitormodeandusermodefunctionasarudimentaryformofprotection(security)system?通过建立一组只能在monitormode才能执行的特权指令集，OS能够确保总是能控制整个系统。2-cont.2.3Whatarethedifferencesbetweenatrapandaninterrupt?Whatistheuseofeachfunction?Aninterrupt是硬件产生的系统内的流的改变Atrap是软件产生的“中断”。interrupt可以被I/O用来产生完成的信号，从而避免CPU对设备的轮询Atrap可以用来调用OS的例程或者捕获算术错误2-cont.2.5Whichofthefollowinginstructionsshouldbeprivileged?a.Setvalueoftimer.b.Readtheclock.c.Clearmemory.d.Turnoffinterrupts.e.Switchfromusertomonitormode.a.Setvalueoftimer.c.Clearmemory.d.Turnoffinterrupts.e.Switchfromusertomonitormode.2-cont.2.8Protectingtheoperatingsystemiscrucialtoensuringthatthecomputersystemoperatescorrectly.Provisionofthisprotectionisthereasonbehinddual-modeoperation,memoryprotection,andthetimer.Toallowmaximumflexibility,however,wewouldalsoliketoplaceminimalconstraintsontheuser.Thefollowingisalistofoperationsthatarenormallyprotected.Whatistheminimalsetofinstructionsthatmustbeprotected?a.Changetousermode.b.Changetomonitormode.c.Readfrommonitormemory.d.Writeintomonitormemory.e.Fetchaninstructionfrommonitormemory.f.Turnontimerinterrupt.g.Turnofftimerinterrupt.b.Changetomonitormode.c.Readfrommonitormemory.d.Writeintomonitormemory.g.Turnofftimerinterrupt.Chapter33.1Whatarethefivemajoractivitiesofanoperatingsysteminregardtoprocessmanagement?用户和系统进程地创建和删除进程的挂起和恢复提供进程同步的机制提供进程通信的机制提供死锁处理的机制3-cont.3.2Whatarethethreemajoractivitiesofanoperatingsysteminregardtomemorymanagement?跟踪内存使用情况（哪一部分被使用、谁使用）当内存空间可用的时候，确定将哪些进程调入内存（job调度）按需要分配和回收内存3-cont.3.3Whatarethethreemajoractivitiesofanoperatingsysteminregardtosecondary-storagemanagement?剩余空间的管理存储分配磁盘调度3-cont.3.4Whatarethefivemajoractivitiesofanoperatingsysteminregardtofilemanagement?文件创建和删除目录创建和删除目录和文件操作原语的支持文件到二级存储的映射将文件备份到非易失存储设备3-cont.3.5Whatisthepurposeofthecommandinterpreter?Whyisitusuallyseparatefromthekernel?读取命令（从用户或者命令文件）并执行（转化成系统调用）可能会经常改变3-cont.3.7Whatisthepurposeofsystemcalls?让用户级进程可以请求操作系统所提供的服务3-cont.3.10Whatisthepurposeofsystemprograms?为程序开发和运行提供了方便的环境给用户提供基本的公共功能函数，为用户在不用自己写代码的情况下解决公用问题试着安装虚拟机VMWARE，然后在这台虚拟机上安装一个操作系统阅读Linux源码，给出某一个systemcall的源码并分析，分析init/main.c给出流程图Chapter44.2Describethedifferencesamongshort-term,medium-term,andlong-termscheduling.Short-term，CPU调度Long-term，job调度Medium-term，分时系统中的中间调度级4-cont.4.4Describetheactionsakerneltakestocontextswitchbetweenprocesses.保存正在运行的进程的状态、恢复欲调度到CPU进程的状态4-cont.4.5Whatarethebenefitsanddetrimentsofeachofthefollowing?Considerboththesystemsandtheprogrammers’levels.a.Symmetricandasymmetriccommunicationb.Automaticandexplicitbufferingc.Sendbycopyandsendbyreferenced.Fixed-sizedandvariable-sizedmessages4-cont.4.6Thecorrectproducer–consumeralgorithminSection4.4allowsonlyn-1bufferstobefullatanyonetime.Modifythealgorithmtoallowallbufferstobeutilizedfully.4-cont.4.7Considertheinterprocess-communicationschemewheremailboxesareused.a.SupposeaprocessPwantstowaitfortwomessages,onefrommailboxAandonefrommailboxB.Whatsequenceofsendandreceiveshoulditexecute?b.WhatsequenceofsendandreceiveshouldPexecuteifPwantstowaitforonemessageeitherfrommailboxAorfrommailboxB(orfromboth)?c.Areceiveoperationmakesaprocesswaituntilthemailboxisnonempty.Eitherdeviseaschemethatallowsaprocesstowaituntilamailboxisempty,orexplainwhysuchaschemecannotexist.areceive(A,m1)receive(B,m2)…send(c,m3)receive(B,m1)receive(A,m2)…send(c,m3)breceive(A,m1)receive(B,m2)…send(c,m3)receive(B,m