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Shortest job next scheduling in operating system-computer world

 Shortest job next scheduling 

Shortest job Next Scheduling (SJN) is also known as shortest job first(SJF). In SJF Scheduling the processes which have the smallest execution time is chosen for the next execution. When the CPU is available, it is assigned to the process that has the smallest next CPU burst. If the next CPU burst of two processes is same then FCFS Scheduling is used to break the tie. SJF Scheduling gives the minimum average waiting time fir a given set of processes. Moving a short process before a long process the waiting time of short process more then it increase the waiting time of long process so the average waiting time decrease. 

Process.                                  Burst time

A1                                                 6

A2                                                 8

A3                                                 7

A4                                                 3

The waiting time for process A1 = 3 millisecond 

The waiting time for process A2 = 16 millisecond 

The waiting time for process A3= 9 millisecond 

The waiting time for process A4 = 0 millisecond 

Thus the average waiting time = (3+16+9+0)/4 =7 millisecond 


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