Non-preemptive Shortest Job First Scheduling Algorithm
Q3. Explain Non-preemptive Shortest Job First Scheduling with example.
Ans. Once CPU is given to the process it cannot be preempted until completes its CPU burst.
Let’s take four processes that arrive at the same time in this order:
Process CPU Time Needed (ms)
P1 6
P2 8
P3 7
P4 3
Gantt Chart:
P4 | P1 | P3 | P2 |
0 3 9 16 24
P1’ waiting time=3
P2’s waiting time=16
P3’s waiting time=9
P4’s waiting time=0
Average Waiting Time
=(3+16+9+0)/4
=28/4
=7 milliseconds
Turnaround Time
Turnaround Time = Burst Time + Waiting Time
Process Turnaround Time
P1 6+3=9
P2 8+16=24
P3 7+9=16
P4 3+0=3
Average Turnaround Time
=(9+24+16+3)/4
=13 milliseconds