Question

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

Process	Execution time	Arrival time
P1 P2 P3 P4	20 25 10 15	0 15 30 45

What is the total waiting time for process P2?

• A. 40
• B. 5
• C. 15
• D. 55

Answer 1

The correct option is C 15

Process Execution Time Arrival Time

$P_1$ 20 0 $P_2$ 25 15 $P_3$ 10 30 $P_4$ 15 45

The Gantt chart for SRT Scheduling algorithm is

$P_1$

$P_2$

$P_3$

$P_2$

$P_4$

0 20 30 40 55 70
So the waiting time for

$P_2=(20-15)+(40-30)=5+10=15$