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1537crumtualiztion1 Mechanisms HIScheduling2 Police
noosingwhichprocess to run
mechanisms at once
TunNprocesseswhile Os maintains
controlsecurity protection
robustness
efficiently
steps
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TBoot Start up
Os runs first establishcontrol
of machine
setsIgeminds to handlevarious service requests
e.ggead a file
app issues a systemcall
Dissuatrapspecial inst
key thing on trapApp SOS
switch motesfrom user kernel
non
privileged privilegedwhen done
refyfromTime line
YET Meat
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osl ti t
How to run many processesat once
Pa PB Pa P
time sharingHood problem
A Process may run
for a long time
Q how to OS regaincontrol Pu
A timer interruptboot set this up
interrupt the CPU
every 1 milliseconds
If I PB7 ter r
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intisaverestate offalots
restore stateof PB
context switch
OS responsibilitytractor each process State
RunningReady not running
could be
what if Process does
something slow
disk I o
Pa readtrap
CPU dOS
g
manyU milliseconds
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Hdesire diskswitch to some other process
when I 0 is issued
mark Pa as Blocked
CuaitingtonI10
switch to PB
Ilo completesmark Pa as Ready
Empletesdesched
schedule
ning Blockedissue
OS Cpu an Ilo
scheduler
U
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ossify queue
FFisionthanks
I É
ight intro to
I É
FileSchedler mem
yqsystemchoosing of
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simplifyingAssumptions about workload
set Tfprocessesprofit that Os needs
to run
Assumptionstart all jobsarrive once
just use CPU no I10
fixed length runs for time T
time is known
metric turnaround time
T T completes Tarrives
Algorithm IT FI FOIF CFS
A B C arrive to
run time I
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Avg TurnaroundActs assuming FIFO
AIME
TA L TB Tc 31
Relax Assumption 3
A B C10 100 10
f EffectAE
T.toTang 80
Newisfestjohti
TAVG
All jobs don't arrive at once
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A 100
rumB
É
B arrives
B 1
Shortest time to CompletionFirst STC F