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Shortest Remaining Time First

An operating system uses Shortest Remaining Time First(SRT) process scheduling algo.Consider the arrival times and execution times for the following processes:

       Process                  Execution Time                  Arrival Time

        P1                                20                                     0

        P2                                25                                    15

        P3                                10                                    30

        P4                                15                                    45

What is the total waiting time for process P2?

Answer

SRT- which process have shorted execution time take CPU first with respect to arrival time.

P1(0-20) P2(20-30) P3(30-40) P2(40-55) P4(55-70

 waiting time(P2)=Compilation Time - Arrival Time - CPU Burst

                          = 55-15-25

                          =15

1Comment
Mohit Lalwani @monty12
27 Jun 2016 09:30 pm

Gantt Chart;

|_p1__|__p1__|__p2___|___p3___|___p2____|______p4_______|
0       15         20           30            40               55                           70  

find waiting time of p2;

Waiting time =completion time-execution time-arrival time;
                      =  55-25-15;
                      =  15