Develop a Gantt Chart, Average Waiting time, FCFS, SJF, RR

RGPV 2020 CPU Scheduling Algorithm

Consider the following set of processes.

Process

Burst Time

Arrival Time

P1

3

0

P2

5

1

P3

2

2

P4

5

3

P5

5

4

Develop a Gantt-chart and calculate the average waiting time using:
i) FCFS
ii) SJF
iii) Round Robin (q = 1)
Solution:

i) FCFS
Gantt Chart for FCFS

From above Gantt Chart waiting time for each process:
Waiting time = Turnaround time – Burst time

Process

Waiting time

P1

3-3=0

P2

7-5=2

P3

8-2=6

P4

12-5=7

P5

16-5=11

Average waiting time = Sum of waiting time / Number of processes
Average waiting time = (0+2+6+7+11)/5 = 5.2
ii) SJF
Gantt Chart SJF

From above Gantt Chart waiting time for each process:
Waiting time = Turnaround time – Burst time

Process 

Waiting time 

P1 

3-3=0 

P2 

9-5=4 

P3 

3-2=1 

P4 

12-5=7 

P5 

16-5=11 

Average waiting time = Sum of waiting time / Number of processes
Average waiting time = (0+4+1+7+11)/5 = 4.6
iii) Round Robin (q = 1)
Gantt Chart RR

From above Gantt Chart waiting time for each process:
Waiting time = Turnaround time – Burst time

Process 

Waiting time 

P1 

11-3=8 

P2 

17-5=12 

P3 

6-2=4 

P4 

16-5=11 

P5 

16-5=11 

Average waiting time = Sum of waiting time / Number of processes
Average waiting time = (8+12+4+11+11)/5 = 9.2