Download Computer Science 8530 Advanced Operating Systems Fall 2016

UNIVERSITYOFNEBRASKAATOMAHA
ComputerScience8530
AdvancedOperatingSystemsFall2016
WrittenHomeworkProblems–Set1
Brief answers to each of the following problems are to be supplied. Complete sentences aren’t even
required, but the intent of the answer must be obvious. Place your answers in a text file, MS Word
document,orPDFfile.Theyshouldbenumberedandappearinthesameorderasshownbelow.Donot
includethequestioninyourresponse–provideONLY youranswer.Youranswersaredueby11:59PM
onThursday,October20.Allquestionshavethesamevalueforevaluationpurposes.
It is imperative that you produce your own answers to these questions. DO NOT SHARE YOUR
ANSWERS WITH OTHER STUDENTS OR ATTEMPT TO OBTAIN ANSWERS FROM
OTHERS.
1. Ithasbeennotedthatourjobincomputerscienceis“tobuildbeautifulnewabstractionsbetween
uglyhardwareandusers.”Identifyatleasttwomajorbeautifulabstractionsofsignificanceto
operatingsystemsprovidedbytheMulticsoperatingsystem.Indicateiftheseabstractionsarestill
beingusedintoday’soperatingsystems.
2. Identifyatleastfivesignificantfeaturesprovidedbyanoperatingsystem.
3. Identifyatleastfivefeaturesthatadvertisingwouldhaveyoubelievearepartsofanoperating
system,butwhicharereallyapplication-leveltools.
4. TheacronymAPIisusedformanythingsthesedays.Withrespecttoanoperatingsystem,whatdo
wemeanbytheAPI?What’sanothertermthat’softenusedfortheoperatingsystem’sAPI?
5. Mostoperatingsystems(certainlythingslikeMSWindows,AppleOSX,andLinux)useseparate
processormodesforusercodeandoperatingsystemcode.Whataretypicalnamesforthese
modes?Howdothesemodesdifferfromeachother?
6. Togetfromthemodewhereuserapplicationsnormallyexecutetothemodewherethekernel
codeisexecutedisusuallydonewithaspecialinstructionassociatedwiththeparticularsystem
architecturebeingused.Identifyatleastoneinstructionthatcanaccomplishthistransitiononthe
Intelx86architectureandonetheARMarchitecture.
7. What’sthedifferencebetweenapparentconcurrencyandrealconcurrency?Giveaspecific
exampleofeachofthese.
8. Xinudevelopmentlinksallapplicationcodetogetherwiththeoperatingsystemcodeandlibrary
codetoproducea“monolithic”executablefile.Thisfileisloadedonce,afterwhichloadingof
additionalcodeisnotrequired.However,theremaybeavariablenumberofprocessesin
execution,evengiventhisfixedcollectionofcode.Howisthatpossible?
9. We’veseenthatXinuhasaparticularlyefficientimplementationforqueuesandlistsofprocesses.
Whataretwothingsintheimplementationthatmaketheimplementationefficient(bothin
memoryutilizationandinexecutiontime)?
10. Summarizethemajordifferencesbetweenport-mappedI/Oandmemory-mappedI/O.Lookatthe
devicedrivercodefortheconsole/serialportinXinuandidentifywhichtypeofI/Oisusedonthe
Galileo.
11. Give,inanorderedlist,thestepsinvolvedatthehardwarelevelwhenafunctionisinvokedand
returns.Forthebodyofthefunction’sexecution,justsay“thefunctionexecuteshere.”Butprecede
andfollowingthiswiththestepsrequiredtoenterthefunction(passingasetofarguments,etc.)
andthestepstakentoleavethefunction(returningaone-wordresult,etc.).
12. What’sthedifferencebetween“polledI/O”and“interrupt-drivenI/O?”Whichofthesedoyou
expecttheMS-DOSoperatingsystemused?Whichwouldbeusedduringearlystagesofsystem
startuptodisplaymessages?Briefly,whataretheadvantagesanddisadvantagesofinterruptdrivenI/OoverpolledI/O?
13. Evenwheninterruptsareusedtoannouncesignificantevents,therearetwomajortechniques
usedtotransfermulti-byte“chunks”ofdatabetweenmemoryandI/Odevices(likenetwork
adaptersanddiskcontrollers).Brieflydescribethese,andindicatewhichislikelytobemore
complexandefficient.
14. DescribethebasiclayoutofmemoryforaCprogram.Indicatethebasiccharacteristicsyou’d
expecttobeassociatedwith“part”ofthememoryassociatedwithaprocessduringitsexecution.
15. What’stheprimaryruleXinuusestodeterminewhichprocessisrunning(orshouldberunning)?
Whichpieceofcode(function)isprimarilyresponsibleforchecking/enforcingthisrule?
16. Provideshortdefinitionsforthetraditionalinterpretationsofthetermsthreadandheavyweight
process.
17. Whereisitlikelythatthemajorityofuser-accessibleregistercontentswillbesavedwhena
processismovedfromtherunning/currentstatetothereadystate?Whereelsemightsomeother
registercontentsbesaved?UseXinuontheGalileoasaspecificcase.
18. Thethreecharacteristicprocessstates(ready,running,andblocked)areextendedsomewhatin
Xinu.Howaretheseextended?Givenamesfortheextendedstatesandbriefdescriptionsofthem.
19. Xinuprovidesamechanismtodeferreschedulingdecisions.Giveanexampleofacasewherethis
deferringofschedulingisappropriate.
20. Thecodetoimplementacontextswitchisoneofthefewrequiredfunctionsinanoperating
systemthatarealmostalwayswritteninassemblylanguage.Whyisthisthecase?
21. Xinuhastwodifferentmemorymanagement“levels”–high-levelandlow-level.Whyarethere
twolevels?Brieflyindicatethemajordifferencesbetweenthemechanismsusedtoallocateand
deallocatememoryateachlevel.
22. Virtualmemorysystemsalwaystrytomaintaina“slushfund”(aswe’vecalleditinclass)of
unused–oratleastavailable–pageframes.Whatalgorithmisused–andwhenitisused–toadd
pageframestothiscollectionofpageframes?Don’tidentifyaspecificalgorithm,butinstead
identifythegeneralnameassociatedwiththeclassofalgorithmsusedforthispurpose.
23. Weoftentalkaboutthetwohalvesofadevicedriver,eventhoughthesepartsarenotofequal
size.Butbothpartsareimportant.Brieflyidentifythemajorfunctionsofeachhalfofthedevice
driverfortheXinu“tty”device.Whichhalfcontainstheinterrupthandler?
24. HowdomostoperatingsystemsavoidhavingtoperformaO(N)searchforworktobedonewhen
theclockticks?Whatisthecomputationalcomplexityassociatedwiththeidentificationoftasks
waitingforaparticulartimetoarrive?
25. Somesystemcallscanbeguaranteedtocompletequickly,likegetpid.Othersystemcallsmay
requireaprocesstobeblockedforsomeperiodoftime,likegetcorreceive.Insomecases,
applicationsmaywishtoabandonsuchasystemcallifittakestoolong.Howcanthisbehandled
bysystems,ingeneral?HowisithandledinXinu.Giveaspecificexample.