What is a prediction How the OS scheduler can predict the CP

What is a prediction? How the OS scheduler can predict the CPU burst in Shortest-Job-First scheduling method?

Solution

Prediction:
Prediction is a statement given about what will happen or might happen in future.
There are different scheduling methods to predict a CPU burst and one of the best method is SJF
Given below how OS scheduler can predict CPU burst by SJF Scheduling
Shortest Job First(SJF) scheduling:

2

in SJF scheduling shortest path is first executed
Hence the GANTT chart will be the following:

0                             2                             5                              11                            32

Now the average time will be=(0+2+5+11)/4=4.5ms

in preemptive SJF,jobs are put into ready queue when they arrived,but a process with shortest burst time arrives,

the existing process is preempited

hence the GANTT chart will be the following:

0                  1                    3                   5                   6                   12                 32

the average time will be: ((5-3)+(6-2)+12-1))/4=4.25ms
the average waiting time for preemptive SJF is less than non preemptive SJF