GATE - 2012 | OS | Consider the 3 processes, P1, P2 and P3 shown in the table.

GATE - 2012 [Operating System]

Question:

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

     

Solution:

Option (C) is Correct.

FCFS is - P1, P2, P3

FCFS is clear.

RR Queue: In RR queue time slot is of 2 units.

Processes are assigned in following order
P1, P2, P1, P3, P2, P1, P3, P2, P2

This question used ready queue concept. 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.

RR2: P1, P3, P2 So option C.

Thank You