操作系统概念第七版答案含编程代码电子教案Word文档格式.docx

操作系统概念第七版答案含编程代码电子教案Word文档格式.docx

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1.1Inamultiprogrammingandtime-sharingenvironment,severaluserssharethesystemsimultaneously.Thissituationcanresultinvarioussecurityproblems.

a.Whataretwosuchproblems?

b.Canweensurethesamedegreeofsecurityinatime-sharedmachineasinadedicatedmachine?

Explainyouranswer.

Answer:

a.Stealingorcopyingone’sprogramsordata;

usingsystemresources（CPU,memory,diskspace,peripherals）withoutproperaccounting.

b.Probablynot,sinceanyprotectionschemedevisedbyhumanscaninevitablybebrokenbyahuman,andthemorecomplexthescheme,themoredifficultitistofeelconfidentofitscorrectimplementation.

1.2Theissueofresourceutilizationshowsupindifferentformsindifferenttypesofoperatingsystems.Listwhatresourcesmustbemanaged

carefullyinthefollowingsettings:

a.Mainframeorminicomputersystemsb.Workstationsconnectedtoserversc.Handheldcomputers

a.Mainframes:

memoryandCPUresources,storage,networkbandwidth.

b.Workstations:

memoryandCPUresouces

c.Handheldcomputers:

powerconsumption,memoryresources.

1.3UnderwhatcircumstanceswouldauserbebetteroffusingatimesharingsystemratherthanaPCorsingle-userworkstation?

Whentherearefewotherusers,thetaskislarge,andthehardwareisfast,time-sharingmakessense.Thefullpowerofthesystemcanbebroughttobearontheuser’sproblem.Theproblemcanbesolvedfasterthanonapersonalcomputer.Anothercaseoccurswhenlotsofotherusersneedresourcesatthesametime.

Apersonalcomputerisbestwhenthejobissmallenoughtobeexecutedreasonablyonitandwhenperformanceissufficienttoexecutetheprogramtotheuser’ssatisfaction.

1.4Whichofthefunctionalitieslistedbelowneedtobesupportedbytheoperatingsystemforthefollowingtwosettings:

（a）handhelddevicesand（b）real-timesystems.a.Batchprogrammingb.Virtualmemoryc.Timesharing

Forreal-timesystems,theoperatingsystemneedstosupportvirtualmemoryandtimesharinginafairmanner.Forhandheldsystems,theoperatingsystemneedstoprovidevirtualmemory,butdoesnotneedtoprovidetime-sharing.Batchprogrammingisnotnecessaryinbothsettings.

1.5Describethedifferencesbetweensymmetricandasymmetricmultiprocessing.Whatarethreeadvantagesandonedisadvantageofmultiprocessorsystems?

Symmetricmultiprocessingtreatsallprocessorsasequals,andI/OcanbeprocessedonanyCPU.AsymmetricmultiprocessinghasonemasterCPUandtheremainderCPUsareslaves.Themasterdistributestasksamongtheslaves,andI/Oisusuallydonebythemasteronly.

Multiprocessorscansavemoneybynotduplicatingpowersupplies,housings,andperipherals.Theycanexecuteprogramsmorequicklyandcanhaveincreasedreliability.Theyarealsomorecomplexinbothhardwareandsoftwarethanuniprocessorsystems.

1.6Howdoclusteredsystemsdifferfrommultiprocessorsystems?

Whatisrequiredfortwomachinesbelongingtoaclustertocooperatetoprovideahighlyavailableservice?

Clusteredsystemsaretypicallyconstructedbycombiningmultiplecomputersintoasinglesystemtoperformacomputationaltaskdistributedacrossthecluster.MultiprocessorsystemsontheotherhandcouldbeasinglephysicalentitycomprisingofmultipleCPUs.Aclusteredsystemislesstightlycoupledthanamultiprocessorsystem.Clusteredsystemscommunicateusingmessages,whileprocessorsinamultiprocessorsystemcouldcommunicateusingsharedmemory.

Inorderfortwomachinestoprovideahighlyavailableservice,thestateonthetwomachinesshouldbereplicatedandshouldbeconsistentlyupdated.Whenoneofthemachinesfail,theothercouldthentake-overthefunctionalityofthefailedmachine.

1.7Distinguishbetweentheclient-serverandpeer-to-peermodelsofdistributedsystems.

Theclient-servermodelfirmlydistinguishestherolesoftheclientandserver.Underthismodel,theclientrequestsservicesthatareprovidedbytheserver.Thepeer-to-peermodeldoesn’thavesuchstrictroles.Infact,allnodesinthesystemareconsideredpeersandthusmayactaseitherclientsorservers-orboth.Anodemayrequestaservicefromanotherpeer,orthenodemayinfactprovidesuchaservicetootherpeersinthesystem.

Forexample,let’sconsiderasystemofnodesthatsharecookingrecipes.Undertheclient-servermodel,allrecipesarestoredwiththeserver.Ifaclientwishestoaccessarecipe,itmustrequesttherecipefromthespecifiedserver.Usingthepeer-to-peermodel,apeernodecouldaskotherpeernodesforthespecifiedrecipe.Thenode（orperhapsnodes）withtherequestedrecipecouldprovideittotherequestingnode.Noticehoweachpeermayactasbothaclient（i.e.itmayrequestrecipes）andasaserver（itmayp