计算机科学-hw操作系统概念课后习题答案-ch13

Chapter:Chapter13

MultipleChoice

1.TheregisterofanI/Oportcanbewrittenbythehosttostartacommandortochange

themodeofadevice.

A)status

B)control

C)data-in

D)transfer

Ans:B

Section:13.2

Difficulty:Medium

2.Aninterruptpriorityschemecanbeusedto.

A)allowthemosturgentworktobefinishedfirst

B)makeitpossibleforhigh-priorityinterruptstopreempttheexecutionofalowpriority

interrupt

C)deferthehandlingoflow-priorityinterruptwithoutmaskingoffallinterrupts

D)Alloftheabove

Ans:D

Section:13.2.2

Difficulty:Difficult

DMAcontrollers.

3A.\

l

zdonotutilizeanadditional,specialpurpose,processor

B\

—

/areanonstandardcomponentinPCsoftoday

c\

)

zcanstealmemoryaccesscyclesfromthemainCPU

D\

l

zcanaccessmainmemoryatthesametimeasthemainCPU

Ans:C

Section:13.2.3

Difficulty:Medium

4

Acharacter-streamdevice.

AX

I

/transfersdatainblocksofbytes

B\

e7transfersdataabyteatatime

\

!

/isadevicesuchasadiskdrive

D\

l

zissimilartoarandomaccessdevice

Ans:B

Section:13.3

Difficulty:Easy

5A.I/Oaccessesablockdeviceasasimplearrayofblocks.

\

l

BzRaw

\

c7Stream

\

D7Indirect

\

l

zCooked

Ans:A

Section:13.3.1

Difficulty:Medium

8

Whichofthefollowingistrueofablockingsystemcall?

A\

J

-Theapplicationcontinuestoexecuteitscodewhenthecallisissued.

BX

J

e/ThecallreturnsimmediatelywithoutwaitingfortheI/Otocomplete.

\

>

zTheexecutionoftheapplicationissuspendedwhenthecallisissued.

D\

J

,Blockingapplicationcodeishardertounderstandthannonblockingapplicationcode

Ans:C

Section:13.3.4

Difficulty:Difficult

7.A(n)isabufferthatholdsoutputforadevicethatcannotacceptinterleaveddata

streams.

AX

I

/escape

B\

l

z

cblockdevice

Dcache

spool

Ans:D

Section:13.4.4

Difficulty:Medium

8.AsensekeyreportsonthefailureofaSCSIdeviceby.

A)statingthegeneralcategoryoffailure

B)statingthegeneralnatureofthefailure

C)givingdetailedinformationabouttheexactcauseoffailure

D)maintaininginternalpagesoferror-loginformation

Ans:B

Section:13.4.5

Difficulty:Medium

9.A(n)isafront-endprocessorthatmultiplexesthetrafficfromhundredsofremote

terminalsintooneportonalargecomputer.

A)terminalconcentrator

B)networkdaemon

C)I/Ochannel

D)contextswitchcoordinator

Ans:A

Section:13.7

Difficulty:Medium

lAoXWhichofthefollowingisaprinciplethatcanimprovetheefficiencyofI/O?

/I

B\Increasethenumberofcontextswitches.

7

cxUsesmalldatatransfers

z)Moveprocessingprimitivesintohardware

D)DecreaseconcurrencyusingDMAcontrollers

Ans:C

Section:13.7

Difficulty:Difficult

Essay

11.Explaintheconceptofabusanddaisychain.Indicatehowtheyarerelated.

Ans:Abusismerelyasetofwiresandarigidlydefinedprotocolthatspecifiesasetof

messagesthatcanbesentonthewires.Themessagesareconveyedbypatternsofelectrical

voltagesappliedtothewireswithdefinedtimings.Adaisychainisadeviceconfigurationwhere

onedevicehasacablethatconnectsanotherdevicewhichhasacablethatconnectsanother

device,andsoon.Adaisychainusuallyoperatesasabus.

Section:13.2

Difficulty:Medium

12.Explainthedifferencebetweenaserial-portcontrollerandaSCSIbuscontroller.

Ans:Aserial-portcontrollerisasimpledevicecontrollerwithasinglechip(orportionofa

chip)thatcontrolsthesignalsonthewiresofaserialport.Bycontrast,aSCSIbuscontrolleris

notsimple.BecausetheSCSIprotocoliscomplex,theSCSIbuscontrollerisoften

implementedasaseparatecircuitboardthatplugsintothecomputer.

Section:13.2

Difficulty:Medium

13.Explaintheconceptofpollingbetweenahostandacontroller.

Ans:Whenahosttriestoaccessthecontroller,itconstantlyreadsthestatusofa"busy

register"andwaitsfortheregistertoclear.Thisrepetitivecheckingistermedpolling.

Section:13.2.1

Difficulty:Medium

14.Whatisinterruptchaining?

Ans:Interruptchainingisatechniqueinwhicheachelementintheinterruptvectorpointsto

theheadofalistofinterrupthandlers.Whenaninterruptisraised,thehandlersonthe

correspondinglistarecalledonebyone,untiloneisfoundthatcanservicetherequest.Thisis

acompromisebetweentheoverheadofahugeinterrupttableandtheinefficiencyofdispatching

toasingleinterrupthandler.

Section:13.2.2

Difficulty:Medium

15.WhyisDMAusedfordevicesthatexecutelargetransfers?

Ans:WithoutDMA,programmedI/Omustbeused.ThisinvolvesusingtheCPUtowatch

statusbitsandfeeddataintoacontrollerregisteronebyteatatime.Therefore,DMAwas

developedtolessentheburdenontheCPU.DMAusesaspecial-purposeprocessorcalleda

DMAcontrollerandcopiesdatainchunks.

Section:13.2.3

Difficulty:Medium

16.Whatisthepurposeofaprogrammableintervaltimer?

Ans:Theprogrammableintervaltimerishardwareusedtomeasureelapsedtimeandtotrigger

operations.Theschedulerusesthismechanismtogenerateaninterruptthatwillpreempta

processattheendofitstimeslice.

Section:13.3.3

Difficulty:Medium

17.GiveanexampleofwhenanapplicationmayneedanonblockingI/Osystemcall.

Ans:Iftheuserisviewingawebbrowser,thentheapplicationshouldallowkeyboardand

mouseinputwhileitisdisplayinginformationtothescreen.Ifnonblockingisnotused,thenthe

userwouldhavetowaitfortheapplicationtofinishdisplayingtheinformationonthescreen

beforeallowinganykindofuserinteraction.

Section:13.3.4

Difficulty:Medium

18.Whatarethethreereasonsthatbufferingisperformed?

Ans:Abufferisamemoryareathatstoresdatawhiletheyaretransferredbetweentwodevices

orbetweenadeviceandanapplication.Onereasonforbufferingishandledatawhenspeed

mismatchesbetweentheproducerandconsumerofadatastreamexist.Thesecondreasonisto

adaptbetweendevicesthathavedifferentdata-transfersizes.Thethirdreasonistosupportcopy

semanticsforapplicationI/O.

Section:13.4.2

Difficulty:Medium

19.WhatisthepurposeofaUNIXmounttable?

Ans:TheUNIXmounttableassociatesprefixesofpathnameswithspecificdevicenames.

Toresolveapathname,UNIXlooksupthenameinthemounttabletofindthelongestmatching

prefix;thecorrespondingentrygivesthedevicename.

Section:13.5

Difficulty:Medium

20.UNIXSystemVimplementsamechanismcalledSTREAMS.Whatisthismechanism?

Ans:STREAMSenablesanapplicationtoassemblepipelinesofdrivercodedynamically.A

streamisafull-duplexconnectionbetweenadevicedriverandauser-levelprocess.Itconsists

ofastreamheadthatinterfaceswiththeuserprocessandadriverendthatcontrolsthedevice.It

mayalsoincludestreammodulesbetweenthem.

Section:13.6

Difficulty:Difficult

True/False

21.Anexpansionbusis