操作系统英文版课后习题答案整理.doc

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.