Question 8835 – Process-Scheduling

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

Correct Answer: C

Question 3 Explanation:

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 the 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 the ready queue after P1. So at t=4, again P1 is executed then P3 is executed for the first time at t=6.
RR2: P1, P3, P2
So option C.

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

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

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

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

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