UGC NET CSE | August 2016 | Part 2 | Question: 40

Question

Consider three CPU intensive processes $P1, P2, P3$ which require $20, 10$ and $30$ units of time, arrive at times $1, 3$ and $7$ respectively. Suppose operating system is implementing Shortest Remaining Time first (preemptive scheduling) algorithm, then _____ context switches are required (suppose context switch at the beginning of Ready queue and at the end of Ready queue are not counted).

• A. $3$ 
• B. $2$
• C. $4$
• D. $5$

Answer 1

p1 ,p2, p3 are three process  

Arrival time of p1 is 1 so we made to run p1 at time 1

now p1 is run for 2 units ( upto 3) new process arrived with less B.T ,so switch happens to p2 ----- (1)

p2 run till completion since there are no shorter jobs available ,then switch happens to p1---- (2)

again p1 is run since it has burst time ( 18 ) < burst time of p3 ( 30 )

completion of p1, switch happens to p3  run till completion.                                               ----- (3)

Answer 2

ANS IS C

CHECK EXPLANATION ON  :http://internetnotes.in/cbse-net-computer-science-august-2016-paper-2-re-test-part-4/

Answer 3

If we consider .and start from 0 then c.s is 4 in question not mention ..so default start from 0 is it correct or wrong plz .look