斯坦福大学操作系统期末考试题英文.docx
《斯坦福大学操作系统期末考试题英文.docx》由会员分享，可在线阅读，更多相关《斯坦福大学操作系统期末考试题英文.docx（8页珍藏版）》请在冰豆网上搜索。
斯坦福大学操作系统期末考试题英文
FINALEXAM–INTRODUCTIONTOOPERATINGSYSTEMSCSE421
May2,2003（Spring2003）
NAME:
_____________________________________________________________
STUDENTNUMBER:
_________-_________
INSTRUCTIONS
Thisisaclosedbookbutyouareallowedtwosheetsofinformationtoreferto.Youhave180minutestocomplete10questions.Pleasewriteneatlyandclearly.Toreceivepartialcredit,youmustshowallworkforyouranswers.Youshouldhave11pagesinthisexambook,someofwhichareblanktoallowroomforyouranswers.
Question
Grade
1
____/20
2
____/20
3
____/10
4
____/14
5
____/20
6
____/16
7
____/10
8
____/10
9
____/10
10
____/10
Total
____/140
RawScore:
___________/140=____________/100
1）[20Points]Deadlock
Considerthefollowingsnapshotofasystem（P=Process,R=Resource）:
Available
RA
RB
RC
RD
8
5
9
7
MaximumDemand
RA
RB
RC
RD
P0
3
2
1
4
P1
0
2
5
2
P2
5
1
0
5
P3
1
5
3
0
P4
3
0
3
3
CurrentAllocation
RA
RB
RC
RD
P0
1
0
1
1
P1
0
1
2
1
P2
4
0
0
3
P3
1
2
1
0
P4
1
0
3
0
Answerthefollowingquestionsusingbanker’salgorithm:
a）CalculatetheNeedsmatrix:
Needs
RA
RB
RC
RD
P0
P1
P2
P3
P4
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
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
0
No
1
No
2
Yes
1
3
No
4
Yes
3
5
No
6
Yes
0
7
Yes
2
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）:
0
Permissionword
1
FileSize
2
Directblock
3
Directblock
4
Directblock
5
Directblock
6
Single-indirect
7
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?
Giveanexample.
3.Whatisacommondatastructureusedtomanage（theslotsfor）nresources?
Giveanexample.
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?
升级会员 