斯坦福大学操作系统期末考试题英文Word文档格式.docx

斯坦福大学操作系统期末考试题英文Word文档格式.docx

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2

3

____/10

4

____/14

5

6

____/16

7

8

9

10

Total

____/140

RawScore:

___________/140=____________/100

1）[20Points]Deadlock

Considerthefollowingsnapshotofasystem（P=Process,R=Resource）:

Available

RA

RB

RC

RD

MaximumDemand

P0

1

P1

P2

P3

P4

CurrentAllocation

Answerthefollowingquestionsusingbanker’salgorithm:

a）CalculatetheNeedsmatrix:

Needs

b）Isthesysteminasafestate?

Ifso,showasafeorderinwhichtheprocessescanrun.

c）CanarequestofoneinstanceofRAbyProcessP0begrantedsafelyaccordingtoBanker’salgorithm?

2）[20points]LogicalandPhysicalAddressSpaces

TheKiwi™memoryarchitecturedesignteamhasadilemma.Theteamisconsideringseveraldifferentmemoryconfigurationvariationsforanupcomingmachinedesign.Considerthefollowingdesigns（Allmemoryaccessesareintermsofbytes,andallareusingpagingtechniques）:

Characteristic

Design1

Design2

Design3

PhysicalMemoryAddressWidth

8bit

16bit

32bit

LogicalAddressWidth

12bit

20bit

24bit

Page/Framesizeinbytes

16bytes

32bytes

64bytes

PageTableType

Single

Double

a）[6points]Foreachdesign,listthemaximumnumberofpageseachprocesscanaccessinlogicaladdressspace.

b）[6points]Foreachdesign,listthemaximumnumberofframesinphysicalmemory.

c）[6points]Fordesign3,iftheoutermostpagetableholds32entries,howmanybitsareneededinthelogicaladdresstorepresenttheouterpagetable?

Howmanybitsareusedforrepresentingtheoffsetwithinapage?

Howmanybitsareneededinthelogicaladdressinordertorepresenttheinnerpagetable?

3）[4+4+2=10points]PageReplacement

Giventhefollowingreferencestring:

021301401234

show

a）Pagefaultsoccurduringtheprocessingofthereferencescheme?

b）Thehitratioisforeachofthefollowingpoliciesinapuredemandpagingsystem?

c）WhatdoyouobservewhenyoumovefromScheme1toScheme2?

Explain.

Scheme1:

FIFOwiththreepagesofmainmemory

Scheme2:

FIFOwithfourpagesofmainmemory

4）[6+4+4=14points]AddressTranslation

Considerasystemwherethevirtualmemorypagesizeis2K（2048bytes）,andmainmemoryconsistsof4pageframes.Nowconsideraprocesswhichrequires8pagesofstorage.Atsomepointduringitsexecution,thepagetableisasshownbelow:

Virtualpage

Valid

Physicalpage

No

Yes

6

1.Listthevirtualaddressrangesforeachvirtualpage.

2.Listthevirtualaddressrangesthatwillresultinapagefault.

3.Givethemainmemory（physical）addressesforeachofthefollowingvirtualaddresses（allnumbersdecimal）:

（i）8500,（ii）14000,（iii）5000,（iv）2100.

Policy:

__________________________________

5）[20points]FileSystemImplementation

Supposeafilesystemisconstructedusingblocksof8wordseach.Inthissystem,awordhasalengthof4bytes.Thediskpackusedtoholdthefilesystemconsistsof32blocks.Theinitialblock（block0）containsadirectoryentry.Thedirectoryentrycontainsthefilenameofasinglefileinthisfilesystem,andapointertothefirstI-nodeinblock1.TheI-nodestructureisasfollows（word,value）:

Permissionword

FileSize

Directblock

Single-indirect

Double-indirect

Thefilecontains16wordsofdata:

thefirstdirectindexpointsatblock31,andtheseconddirectindexpointsatblock29.Blocks4,7,10,and15aremarkedbad.Assumethatfreeblocksareallocatedinlogicalorderstartingwithblock0andthatwriteoperationsmodifythefilesystem1blockatatime.

Whatwillthestateofthesystemlooklikeafter100additionalwordsareappendedtothefile（drawablockdiagramshowingthestructureoftheI-nodeandtheblocksthatareallocated）

6）[16points]DiskScheduling

Diskrequestscomeintothediskdriverforcylinders10,22,20,2,40,6,and38,inthatorder.Assumethatthediskhas100cylinders.

Aseektakes6msecpercylindermoved.Computetheaverageseektimefortherequestsequencegivenabovefor

1.First-come,First-served

2.ShortestSeekTimeFirst（SSTF）

3.LOOK（withthedisk-arminitiallymovingtowardshighernumbercylindersfromlowernumbercylinders）

4.C-SCAN

Inallthecases,thearmisinitiallyatcylinder20.

7）[10points]Security:

PublicKeyEncryption

ConsiderthepublickeyencryptiondefinedbytheRSA（Rivest,Shamir,Adelman）scheme.Assumethatthetwostartingprimesarepandqare3and7respectivelyanddeterminethe（nontrivial）privatekeyandpublickeypairsaccordingtotheRSAscheme.

8）[10Points]Networking:

TCP/IP

ThefollowingflowchartshowstheclientandserverportionsofaTCPcommunicationsession.Fillintheemptybubbles/boxeswiththeappropriatesocketsystemcallnames.

CLIENTSERVER

9）[10points]EnduringPrinciplesinSystemDesign

1.Whenasystemgetscomplexindesignwhatisacommonsolutiontomanagethecomplexity?

Giveanexample.

2.Whenyouexperienceincompatibilitiesbetweensystemmodules,howwillyousolvethisproblem?

3.Whatisacommondatastructureusedtomanage（theslotsfor）nresources?

4.Thedataitemssuchasinodesandfilesaretypicallylocatedinexternalmemorythatissluggishrelativetothelocalmainmemory.Howaretheeffectiveaccesstimesofthesestructuresminimized?

5.Whenatablemaintainingalistofpointersgrowsunmanageablylargehowwillyousolvethisproblemsothat（i）searchtimesofthetableisreasonableand（ii）onlytheregionofinterestinthetableneedtobeinthememory?

10）[10points]NachosOperatingSystems

1.Listthetwomainoperations（methods）thathavethepotentialforresultinginapagefault.

2.Whereistheaddressthatcausedthepagefaultstored?

3.YouincrementedthePCaftereverysystemcallyouimplemented?

Whynotforpagefaultsystemcall?

4.WhatisthepurposeofExec,JoinandExitsystemcalls?

5.Explaintheabovewithanexample.

6.Howwouldyoucontroltheaccesstoasharedresourcebymultiplethreads?