操作系统英文版课后习题答案整理.doc
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14
OSExerciseBook
ClassNo.Name
1.1Whatarethethreemainpurposesofanoperatingsystem?
（1）Interfacebetweenthehardwareanduser;
（2）managetheresourceofhardwareandsoftware;
（3）abstractionofresource;
1.2Listthefourstepsthatarenecessarytorunaprogramonacompletelydedicatedmachine.
Preprocessing>Processing>Linking>Executing.
1.6Definetheessentialpropertiesofthefollowingtypesofoperatingsystems:
a.Batch
b.Interactive
c.Timesharing
d.Realtime
e.Network
f.Distributed
1.7Wehavestressedtheneedforanoperatingsystemtomakeefficientuseofthecomputing
hardware.Whenisitappropriatefortheoperatingsystemtoforsakethisprincipleandto“waste”resources?
Whyissuchasystemnotreallywasteful?
2.2Howdoesthedistinctionbetweenmonitormodeandusermodefunctionasarudimentary
formofprotection（security）system?
2.3Whatarethedifferencesbetweenatrapandaninterrupt?
Whatistheuseofeachfunction?
2.5Whichofthefollowinginstructionsshouldbeprivileged?
a.Setvalueoftimer.
b.Readtheclock.
c.Clearmemory.
d.Turnoffinterrupts.
e.Switchfromusertomonitormode.
2.8Protectingtheoperatingsystemiscrucialtoensuringthatthecomputersystemoperates
correctly.Provisionofthisprotectionisthereasonbehinddual-modeoperation,memory
protection,andthetimer.Toallowmaximumflexibility,however,wewouldalsoliketo
placeminimalconstraintsontheuser.
Thefollowingisalistofoperationsthatarenormallyprotected.Whatistheminimalset
ofinstructionsthatmustbeprotected?
a.Changetousermode.
b.Changetomonitormode.
c.Readfrommonitormemory.
d.Writeintomonitormemory.
e.Fetchaninstructionfrommonitormemory.
f.Turnontimerinterrupt.
g.Turnofftimerinterrupt.
3.6Listfiveservicesprovidedbyanoperatingsystem.Explainhoweachprovidesconveniencetotheusers.Explainalsoinwhichcasesitwouldbeimpossibleforuser-levelprogramstoprovidetheseservices.
3.7Whatisthepurposeofsystemcalls?
3.10Whatisthepurposeofsystemprograms?
4.1MS-DOSprovidednomeansofconcurrentprocessing.Discussthreemajorcomplications
thatconcurrentprocessingaddstoanoperatingsystem.
4.6Thecorrectproducer–consumeralgorithminSection4.4allowsonlyn-1bufferstobe
fullatanyonetime.Modifythealgorithmtoallowallbufferstobeutilizedfully.
5.1Providetwoprogrammingexamplesofmultithreadinggivingimproveperformanceover
asingle-threadedsolution.
5.3Whataretwodifferencesbetweenuser-levelthreadsandkernel-levelthreads?
Underwhatcircumstancesisonetypebetterthantheother?
6.3Considerthefollowingsetofprocesses,withthelengthoftheCPU-bursttimegivenin
milliseconds:
Process Burst TimePriority
P1 10 3
P2 1 1
P3 2 3
P4 1 4
P5 5 2
TheprocessesareassumedtohavearrivedintheorderP1,P2,P3,P4,P5,allattime0.
a.DrawfourGanttchartsillustratingtheexecutionoftheseprocessesusingFCFS,SJF,anonpreemptivepriority（asmallerprioritynumberimpliesahigherpriority）,andRR
（quantum=1）scheduling.
b.Whatistheturnaroundtimeofeachprocessforeachoftheschedulingalgorithmsin
parta?
c.Whatisthewaitingtimeofeachprocessforeachoftheschedulingalgorithmsinpart
a?
d.Whichoftheschedulesinpartaresultsintheminimalaveragewaitingtime（overall
processes）?
Answer:
6.4Supposethatthefollowingprocessesarriveforexecutionatthetimesindicated.Each
processwillrunthelistedamountoftime.Inansweringthequestions,usenonpreemptive
schedulingandbasealldecisionsontheinformationyouhaveatthetimethedecision
mustbemade.
a.WhatistheaverageturnaroundtimefortheseprocesseswiththeFCFSscheduling
algorithm?
b.WhatistheaverageturnaroundtimefortheseprocesseswiththeSJFschedulingalgorithm?
c.TheSJFalgorithmissupposedtoimproveperformance,butnoticethatwechoseto
runprocessP1attime0becausewedidnotknowthattwoshorterprocesseswould
arrivesoon.ComputewhattheaverageturnaroundtimewillbeiftheCPUisleft
idleforthefirst1unitandthenSJFschedulingisused.RememberthatprocessesP1
andP2arewaitingduringthisidletime,sotheirwaitingtimemayincrease.This
algorithmcouldbeknownasfuture-knowledgescheduling.
6.10Explainthedifferencesinthedegreetowhichthefollowingschedulingalgorithmsdiscriminateinfavorofshortprocesses:
a.FCFS
b.RR
c.Multilevelfeedbackqueues
7.7Showthat,ifthewaitandsignaloperationsarenotexecutedatomically,
thenmutualexclusionmaybeviolated.
7.8TheSleeping-BarberProblem.Abarbershopconsistsofawaitingroomwithnchairsandthebarberroomcontainingthebarberchair.Iftherearenocustomerstobeserved,thebarbergoestosleep.Ifacustomerentersthebarbershopandallchairsareoccupied,thenthecustomerleavestheshop.Ifthebarberisbusybutchairsareavailable,thenthecustomersitsinoneofthefreechairs.Ifthebarberisasleep,thecustomerwakesupthebarber.Writeaprogramtocoordinatethebarberandthecustomers.
8.2Isitpossibletohaveadeadlockinvolvingonlyonesingleprocess?
Explainyouranswer.
8.4ConsiderthetrafficdeadlockdepictedinFigure8.11.
a.Showthatthefournecessaryconditionsfordeadlockindeedholdinthisexample.
b.Stateasimplerulethatwillavoiddeadlocksinthissystem.
8.13
Considerthefollowingsnapshotofasystem:
Allocation
Max
Available
ABCD
ABCD
ABCD
P0
0012
0012
1520
P1
1000
1750
P2
1354
2356
P3
0632
0652
P4
0014
0656
Answerthefollowingquestionsusingthebanker’salgorithm:
a.WhatisthecontentofthematrixNeed?
b.Isthesysteminasafestate?
c.IfarequestfromprocessP1arrivesfor（0,4,2,0）,cantherequestbegrantedimmediately?
9.5Givenmemorypartitionsof100K,500K,200K,300K,and600K（inorder）,howwouldeach
oftheFirst-fit,Best-fit,andWorst-fitalgorithmsplaceprocessesof212K,417K,112K,and426K（inorder）?
Whichalgorithmmakesthemostefficientuseofmemory?
9.8Consideralogicaladdressspaceofeightpagesof1024wordseach,mappedontoaphysical
memoryof32frames.
a.Howmanybitsarethereinthelogicaladdress?
b.Howmanybitsarethereinthephysicaladdress?
9.16Considerthefollowingsegmenttable:
Segment Base Length
0 219 600
1 2300 14
2 90 100
3 1327 580
4 1952 96
Whatarethephysicaladdressesforthefollowinglogicaladdresses?
a.0,430
b.1,10
c.2,500
d.3,400
e.4,112
10.2Assumethatyouhaveapagereferencestringforaprocesswithmframes（initiallyallempty）.Thepagereferencestringhaslengthpwithndistinctpagenumbersoccurinit.Foranypage-replacementalgorithms,
a.Whatisalowerboundonthenumberofpagefaults?
b.Whatisanupperboundonthenumberofpagefaults?
10.11Considerthefollowingpagereferencestring:
1,2,3,4,2,1,5,6,2,1,2,3,7,6,3,2,1,2,3,6.
Howmanypagefaultswouldoccurforthefollowingreplacementalgorithms,assumingone,two,three,four,five,six,orsevenframes?
Rememberallframesareinitiallyempty,soyourfirstuniquepageswillallcostonefaulteach.
LRUreplacement
FIFOreplacement
Optimalreplacement
11.7Explainthepurposeoftheopenandcloseoperations.
11.9Giveanexampleofanapplicationinwhichdatainafileshouldbeaccessedinthefollowingorder:
a.Sequentially
b.Randomly
11.12Considerasystemthatsupports5000users.Supposethatyouwanttoallow4990oftheseuserstobeabletoaccessonefile.
a.HowwouldyouspecifythisprotectionschemeinUNIX?
b.Couldyousuggestanotherprotectionschemethatcanbeusedmoreeffectivelyfor
thispurposethantheschemeprovidedbyUNIX?
12.1Considerafilecurrentlyconsistingof100blocks.Assumethatthefilecontrolblock（and
theindexblock,inthecaseofindexedallocation）isalreadyinmemory.Calculatehow
manydiskI/Ooperationsarerequiredforcontiguous,linked,andindexed（single-level）
allocationstrategies,if,foroneblock,thefollowingconditionshold.Inthecontiguousallocationcase,assumethatthereisnoroomtogrowinthebeginning,butthereisroomtogrowintheend.Assumethattheblockinformationtobeaddedisstoredinmemory.
a.Theblockisaddedatthebeginning.
b.Theblockisaddedinthemiddle.
c.Theblockisaddedattheend.
d.Theblockisremovedfromthebeginning.
e.Theblockisremovedfromthemiddle.
f.Theblockisremovedfromtheend.
13.2ConsiderthefollowingI/Oscenariosonasingle-userPC.
a.Amouseusedwithagraphicaluserinterface
b.Atapedriveonamultitaskingoperatingsystem（assumenodevicepreallocationis
available）
c.Adiskdrivecontaininguserfiles
d.Agraphicscardwithdirectbusconnection,accessiblethroughmemory-mapped
I/O
ForeachoftheseI/Oscenarios,wouldyoudesigntheoperatingsystemtousebuffering,
spooling,caching,oracombination?
WouldyouusepolledI/O,orinterrupt-drivenI/O?
Givereasonsforyourchoices.
14.2Supposethatadiskdrivehas5000cylinders,numbered0to4999.Thedriveiscurrently
servingarequestatcylinder143,andthepreviousrequestwasatcylinder125.Thequeue
ofpendingrequests,inFIFOorder,is
86,1470,913,1774,948,1509,1022,1750,130
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