CHAPTER9VirtualMemoryPracticeExercises
9.1Underwhatcircumstancesdopagefaultsoccur?Describe
theactionstakenbytheoperatingsystemwhenapagefault
occurs.
Answer:
Apagefaultoccurswhenanaccesstoapagethathasnot
been
broughtintomainmemorytakesplace.Theoperating
systemveri?es
thememoryaccess,abortingtheprogramifitisinvalid.Ifit
isvalid,afreeframeislocatedandI/Oisrequestedtoreadthe
neededpageintothefreeframe.UponcompletionofI/O,the
processtableandpagetableareupdatedandtheinstructionis
restarted.
9.2Assumethatyouhaveareferencestringfora
processwithmframes(initiallyallempty).Thereference
stringhaslengthp;
ndistinctpagenumbersoccurinit.Answerthesequestions
foranyreplacementalgorithms:
a.Whatisalowerboundonthenumberofpagefaults?
b.Whatisanupperboundonthenumberofpagefaults?
Answer:
a.n
b.p
9.3ConsiderthepagetableshowninFigure9.30forasystem
with12-bitvirtualandphysicaladdressesandwith256-byte
pages.Thelistoffree
pageframesisD,E,F(thatis,Disattheheadofthelist,Eis
second,andFislast).
Convertthefollowingvirtualaddressestotheirequivalent
physicaladdressesinhexadecimal.Allnumbersaregivenin
hexadecimal.(Adashforapageframeindicatesthatthepageis
notinmemory.)
9EF
111
2930Chapter9VirtualMemory
700
0FF
Answer:
9EF-0EF
111-211
700-D00
0FF-EFF
9.4Considerthefollowingreplacementalgorithms.
Rankthesealgorithmsona?ve-pointscalefrom“bad”to
“pe
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