#OS #MULTILEVEL FEEDBACK QUEUE

Question

Consider a system which has a CPU bound process,which require the burst time of 40 seconds.The multilevel Feed Back Queue scheduling algorithm is used and the queue time quantum '2' seconds and in each level it is incremented by '5' seconds.Then how many times the process will be interrupted and on which queue the process will terminate the execution?

(a) 5,4  (b) 4,5 (c) 3,4  (d) 4,3

Answer 1

Process P needs 40 Seconds for total execution. 
Multilevel Feedback queue:
Queue1 = 2
Queue2 = 7  (2+5)
Queue3 = 12 (7+5)
Queue4 = 17 (12+5)
Queue5 = 2  (left time)

hence you can see process is interrupted 4 times, and on 5th qeueue 
process completed its execution.
Hence, (b) is correct option

 

Answer 2

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Comments

your level 2 should be level 1 and so on

Answer 3

level 1==> 40-2=38(interrupted)

level 2==> 38-(2+5)=31(interrupted)

level 3==> 31-(2+5+5)=19(interrupted)

level 4==>19-(2+5+5+5)=2(interrupted)

level 5==>2<(2+5+5+5+5) so terminate successfully.

so total interrupt=4 ,and process will terminate at 5th queue

Answer 4

l1     TQ=2sec(2units of job done)

l2     TQ=(2+5=7sec)(2+7=9 units of job done)

l3     TQ=(7+5=12sec)(9+12=21 units of job done)

l4     TQ=(12+5=17sec)(21+17=38 units of job done)

l5     TQ=(17+5=22sec)(38+22=60 units of job can be done but we are remaining with 2 units of job hence it will run only for 2sec)

no. of interrupts =4

ie. from l1 to l2 =1

     from l2 to l3 =2

     from l3 to l4 =3

     from l4 to l5 =4