Shortest job first scheduling

Shortest job first scheduling
Key concept of this algorithm is: “CPU is allocated to the process with least CPU-burst time.” Amongst the processes in the ready queue. CPU is always assigned to the process with least CPU burst requirement. If the two processes having the same length, next CPU burst, fcfs scheduling is used i.e. one which arrives first, will be taken up first by the CPU.

This algorithm can be preemptive or non-preemptive.

Let us consider, the following set of processes having their CPU burst time mentioned in millisecond and having arrived almost at the same time.

process CPU Burst Time
p1 10
p2 5
p3 2

The Gantt chart:

shortest job first scheduling

shortest job first scheduling

Waiting time for P3 = 0 millisecond
Waiting time for P2= 2 millisecond
Waiting time for P1 = 7 millisecond
Average waiting time= (0+2+7) /3 = 3 millisecond

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