操作系统英文版课后习题答案整理word文档良心出品.docx

操作系统英文版课后习题答案整理word文档良心出品.docx

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操作系统英文版课后习题答案整理word文档良心出品

l.lWhatarethethreemainpurposesofanoperatingsystem?

⑴Interfacebetweenthehardwareanduser;

（2）managetheresourceofhardwareandsoftware;

（3）abstractionofresource;

Answer:

•Toprovideanenvironmentk>racomputeruserto

•Tb吕lk>cat特the艺t?

parattzresourcesofthecompulerasntededtostrivetheprtjblemgiven*Theallocationptocessshouldbeasfairandefficientaspossible.

•Asact>ntroJpa>gramitservestwomajorfunctions：

（1）supervisionoftheexecutionofuserprogramstopreventerrorsandimproperuseofthecomputer,and

（2）managementofthe«peratit）JIandcontrolof[/Odevices.

1.2Listthefourstepsthatarenecessarytorunaprogramonacompletelydedicatedmachine.Preprocessing>Processing>Linking>Executing.

Answer

乩Reservemachinetime*

b.Manuallyloadprogramintomemory.

c.Loadstartingaddressandbeginexecution.

d.Monitorandcontrolexecutionofprogramfnimct>nsoie.

1.6Definetheessentialpropertiesofthefollowingtypesofoperatingsystems:

a.Batch

b.Interactive

c.Timesharing

d.Realtime

e.Network

f.Distributed

Answer

a”

b.

c.

Batch.Jobswithsimilarneedsarebatchedtogetherandrunthroughthecomputerasagrcupbyanoperatororautomaticjobst^quencer.[咆jrformHrk：

电isincreasedbyatteiTiptingtokeepCPUandI/Odevicesbusv試alltimesthroughoff-line

operation,Kptx?

ling,andmultiprogramming*Batchisgoodforexecutinglargejobsthatnetxlinteraction;itcanbesiubmiltedandpickeduplater

Interactive.ThkinJofmanyshorttransactiorifdwheretheresultsof

thenexttransactionmaybeunpredictable.Responserirneneedstobeshort（seconds]sincetheusersubmilsandw^iihFortheresult.

Timesharing.Thissystemsu&es匚nschedulingandmLiltiprt）grammingtoprtividt*economicalinteractiveofasystem.TheCP匚占w让chemrapidlyfn>nnoneusertoanotherInsteadofhavingajobdefinedbyspooledcardimages^eachprogramre^ds

itsnextcontrolcardfromtheterminal,andoutputisnormallyprintedimmediatelytothescreen.

d.

Realtime.Oftenusvdinadedicatedapplication,tliissystemreadsinformationframsensorsandmustrespondwithinafixedamountoftimetoensurecorrectperformance-

Network.

Distributed.Thissystemdistributescomputationarntmgse¥t?

ralphysicalprtxzesKors,Theprt>cesst>rsdonotsharememoryoracltKk.Instead,eachprixessorhasitst>wnkxzalmemory.Theycommunicatewitheachotherthroughvariouscommunicatitmlines,suchasahigh-speedbusortelephoneline.

Wehavestressedtheneedforanoperatingsystemtomakeefficientuseofthecomputing

1.7

hardware.Whenisitappropriatefortheoperatingsystemtoforsakethisprincipleandtowaste"resources?

Whyissuchasystemnotreallywasteful?

AnswerSingle*usersystemsshtiuIdmaximizeuseofthesystennfortheuser.AGUImight“waste"CPUcy

2.2Howdoesthedistinctionbetweenmonitormodeandusermodefunctionasarudimentaryformofprotection（security）system?

亠■■

Answer;Byestablishingasetofprivilegedinstructionsthatcanbeexecutedonlywheninthemt>niu）rmode,theoperatingsystemisassuredofct^ntrollingtheentiresystematalltimes.

2.3Whatarethedifferencesbetweenatrapandaninterrupt?

Whatistheuseofeachfunction?

AnswerAninterruptisahardware-generatedchange-of-flowwithinthesystem.Aninterrupthandlerissummonedtodealwiththec

turnedtotheinterruptedcontextandinstruction.Atrapisasoftware-generatedinterrup匕AninterruptcanbvusvdtosignalthecoiTipJctk*nofan[/Otoobviatetheneedfnrdu\icypoiling.Atrapcanbeusedtocalloperatingsystemroutinesortocatcharithmeticerrors.

2.5Whichofthefollowinginstructionsshouldbeprivileged?

a.Setvalueoftimer.

b.Readtheclock.

c.Clearmemory.

d.Turnoffinterrupts.

e.Switchfromusertomonitormode.

Answer:

Thefollowinginstructionsshouldbeprivileged:

a.Setvalueoftimer.

b.Clearmemory.

c.Turnoffinterrupta

cLSwitchfromusertomonitormode.

2.8Protectingtheoperatingsystemiscrucialtoensuringthatthecomputersystemoperatescorrectly.Provisionofthisprotectionisthereasonbehinddual-modeoperation,memoryprotection,andthetimer.Toallowmaximumflexibility,however,wewouldalsoliketoplaceminimalconstraintsontheuser.

Thefollowingisalistofoperationsthat

ofinstructionsthatmustbeprotected?

a.Changetousermode.

b.Changetomonitormode.

c.Readfrommonitormemory.

d.Writeintomonitormemory.

e.Fetchaninstructionfrommonitormemory.

f.Turnontimerinterrupt.

g.Turnofftimerinterrupt.

AnswenTheminimalsetofinstructionsthatmustbeprotectedare:

b.

c.

Readfrommonitormemory*

Writeintomonitormemorv.

*

Turnofftimerinterrupt.

3.6Listfiveservicesprovidedbyanoperatingsystem.Explainhoweachprovidesconveniencetotheusers.Explainalsoinwhichcasesitwouldbeimpossibleforuser-level

programstoprovidetheseservices.

Answer:

Programexecution.Theoperatingsystemloadsthecontents（orsections）ofafileintomemoryandbeginsitsexecution.Auser-levelpm呂ramcouldnotbetrustedtoproperlyallocateCPUtime.

I/O'operations.Disks,tapes,seriallines^andotherdevicesmustbecommunicatedwithata\erylowlevel.Theuserneedonlyspecifythedeviceandtheoperationtoperformonit,whilethesystemconvertsthatrequestintodevice-orcontroller-specificcommands.User-levelprogramscannotbetrustedtoonlyaccessdevicestheyshouldhaveaccesstonndtoonlyaccessthemwhentheyartotherwiseunused.

File-systemmanipulation.Therearvmanydetailsinfilecreation,deletion,alkKation,andnamingthatusersshouldnothavetoperform.Blocksofdiskspact?

areusedbyfilesandmustbetracked.Deletingafilerequiresremovingthenamefileinformationandfreeingthe说[locatedbk>cks.[Protectionsmustalsobecheckedtoassureprtiperfileaccess.Userprt^gramscouldneitherensureadherencetctprotectionmethexJsnorbetrustedtoallocateonlyfreeblocksanddeallocateblocksonfiledeletion.

Communications.Messagepassingbetweensystemsrequiresmessagesbeturnedintopacketsofinformation,senttothenetworkcontnUlei;transmittedacrossacommunicationsmedium,andreassembledbythedestinationsystem.Packetorderinganddatacorrectionmusttakeplace.Again,userprogramsmightnotcoordinateaccesstothenetworkdevice,ortheymightreevi^Tpacketsdestinedforotherprocesses.

•Errordetection.Errordetectionoccursatboththehardwareandsofirwarelevels.Atthehardwarele\-el,alldatatransfersmustbeinspectedtoensurethatdatahavenotbeenc（>rruptedintransitAUdataonmediamustbicheckedtobesuretheyhavenotchangedsincetheywerewrittentothemedia.Atthesoftwarelevel,mediamustbecheckedfordataconsistency；forinstance,dothenumberofallt>catedandunallocatedblocksofstoragematchthetotalnumberonthedevice.There,errorsarefrequentlyprexzess-independent（forinstance,thecorruptionofdataonadisk）,sotheremustbeaglobalprogram（ttiEoperatingsystem）thathandlesalltype吕oferrors.Also,byhavingerrorsprocessedbytheoperatingsystem,processesneednotcontaincodetocatchandcorrectallthEerrorspossibleonasystEm.

3.7Whatisthepurposeofsystemcalls?

AnswerSystemualls（j1U>wuser-lewlliirequesticesuftl咤uperdtingsv;»-

tem.

3.10Whatisthepurposeofsystemprograms?

jVnswcr:

Evstemprogramscanbethoughtofbundlcz^ufusefulsystctuoils.Tbev

providebasicfuncticrahtytousersandsousersdenotneedtowritetheirownprogramstosol、忙commonproblems.

4.1MS-DOSprovidednomeansofconcurrentprocessing.Discussthreemajorcomplicationsthatconcurrentprocessingaddstoanoperatingsystem.

Answer:

Amethodoftimesharingmustbeimplementedtoalloweachofseveralprocessestohaveaccesstothesysten'i.ThismethodinxoJvcsthepromptionofprocessesthatdonotvoluntarilygiA-euptheCPU（byusingasystemcal],forinstance）

Processesandsystemresourcesmusthaveprotectionsandmustbeprciteck?

dfrtiTneachotherAnygivenprocessmustbelimitedintheamountofmemoryitcanuseandtheoperationsitcanperformondeviceslikedisks.

Thecorrectproducer—consumeralgorithminSection4.4allowsonlyn-1bufferstobe

Caremustbetakeninthekerneltopre\entdeadkxzksbetweenprocesse鬲soprcicessesaren'twaitingforeachother'sallcxatedrest>urces.

4.6

fullatanyonetime.Modifythealgorithmtoallowallbufferstobeutilizedfully.

AnswerNoanswer.

5.1Providetwoprogrammingexamplesofmultithreadinggivingimproveperformaneeover

asingle-threadedsolution.

Answer

（1）Aserverthatserviceseachrequestinaseparatethread.

（2）Aparal*lelizedapplicationsuchasmatrixmultiplicationwheredifferentpartsofthematrixmaybeworkedoninparallel.（3）AninteractiveGUIprogramsuchasadibuggerwhereathreadisusedtomonitoruserinput,anotherthreadrepresentstherunningflppHcation,andathirdthreadmonitorsperformance.

5.3Whataretwodifferencesbetweenuser-levelthreadsandkernel-levelthreads?

Under

whatcircumstancesisonetypebetterthantheother?

r■

AnswerContextswitchingbetweenusertlireadsisquitesimilartGswitchingbetweenkernelthreads,althoughitis