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1、solutionstotheexercisesChapter11.1Inamultiprogrammingandtime-sharingenvironment,severaluserssharethesystemsimultaneously.Thissituationcanresultinvarioussecurityproblems.a.Whataretwosuchproblems?b.Canweensurethesamedegreeofsecurityinatime-sharedmachineasinadedicat
2、edmachine?Explainyouranswer.Answer:a.Stealingorcopyingone痴programsordata;usingsystemresources(CPU,memory,diskspace,peripherals)withoutproperaccounting.b.Probablynot,sinceanyprotectionschemedevisedbyhumanscaninevitablybebrokenbyahuman,andthemorecomplexthescheme,th
3、emoredifficultitistofeelconfidentofitscorrectimplementation.1.2Theissueofresourceutilizationshowsupindifferentformsindifferenttypesofoperatingsystems.Listwhatresourcesmustbemanagedcarefullyinthefollowingsettings:a.Mainframeorminicomputersystemsb.Workstationsconne
4、ctedtoserversc.HandheldcomputersAnswer:a.Mainframes:memoryandCPUresources,storage,networkbandwidth.b.Workstations:memoryandCPUresoucesc.Handheldcomputers:powerconsumption,memoryresources.1.3Underwhatcircumstanceswouldauserbebetteroffusingatimesharingsystemrathert
5、hanaPCorsingle-userworkstation?Answer:Whentherearefewotherusers,thetaskislarge,andthehardwareisfast,time-sharingmakessense.Thefullpowerofthesystemcanbebroughttobearontheuser痴problem.Theproblemcanbesolvedfasterthanonapersonalcomputer.Anothercaseoccurswhenlotsofoth
6、erusersneedresourcesatthesametime.Apersonalcomputerisbestwhenthejobissmallenoughtobeexecutedreasonablyonitandwhenperformanceissufficienttoexecutetheprogramtotheuser痴satisfaction.1.4Whichofthefunctionalitieslistedbelowneedtobesupportedbytheoperatingsystemforthefol
7、lowingtwosettings:(a)handhelddevicesand(b)real-timesystems.a.Batchprogrammingb.Virtualmemoryc.TimesharingAnswer:Forreal-timesystems,theoperatingsystemneedstosupportvirtualmemoryandtimesharinginafairmanner.Forhandheldsystems,theoperatingsystemneedstoprovidevirtual
8、memory,butdoesnotneedtoprovidetime-sharing.Batchprogrammingisnotnecessaryinbothsettings.1.5Describethedifferencesbetweensymmetricandasymmetricmultiprocessing.W
