GATE | GATE CS 2012 | Question 65

Consider the 3 processes, P1, P2 and P3 shown in the table.

Process           Arrival time         Time Units Required
   P1                0                         5
   P2                1                         7
   P3                3                         4

The completion order of the 3 processes under the policies FCFS and RR2 (round robin scheduling with CPU quantum of 2 time units) are
(A)

FCFS: P1, P2, P3
 RR2: P1, P2, P3

(B)

 FCFS: P1, P3, P2
 RR2: P1, P3, P2

(C)

FCFS: P1, P2, P3
 RR2: P1, P3, P2

(D)

FCFS: P1, P3, P2 
RR2: P1, P2, P3

Answer: (C)

Explanation:

FCFS is clear.  

In RR, time slot is of 2 units.  

Processes are assigned in following order
p1, p2, p1, p3, p2, p1, p3, p2, p2

This question involves the concept of ready queue. At t=2, p2 starts and p1 is sent to the ready queue and at t=3 p3 arrives so then the job p3 is queued in ready queue after p1. So at t=4, again p1 is executed then p3 is executed for first time at t=6.

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