Question

An operating system uses shortest remaining time (SRT) scheduling algorithm. Consider the arrival times and execution time for the following processes:

Proces	Arrival Time	Execution Time
P1	0	20
P2	15	25
P3	30	10
P4	45	15

What is total waiting time for process P2?

1. 5
2. 15
3. 40
4. 55

Answer 1

Correct Answer - Option 2 : 15

Shortest remaining time (SRT)  is pre-emptive algorithms

Gantt chart:

P1

P2

P3

P2

P4

0      20      30      40     55      70

Process Table:

Process	Arrival Time	Execution Time (Burst Time)	Completion Time	Turnaround time	Waiting time
P1	0	20
P2	15	25	55	40	15
P3	30	10
P4	45	15

 

Explanation:

Completion time For P2 =55

Turn around time (TAT) = Completion time - Arrival time = 55 -15 = 40

Waiting Time for P2  = TAT-Execution Time = 40- 25 =15

Therefore waiting time P2 is 15 unit: