Round Robin scheduling Exercise with solution

Question 1:

Given the following processes with their arrival times and burst times, calculate the turnaround time and waiting time for each process using – Round Robin scheduling with a time quantum of 3 units.

Process ID	Arrival Time	Burst Time
P1	0	5
P2	1	4
P3	2	6
P4	3	2

Steps to Solve

Construct the Gantt Chart:
- Process the tasks in order of their arrival and given burst times.
Track remaining times and process scheduling:
- P1: Remaining time 5
- P2: Remaining time 4
- P3: Remaining time 6
- P4: Remaining time 2

Gantt Chart Construction

Using a time quantum of 3 units:

Time 0-3: P1 runs for 3 units (remaining time 2)
Time 3-6: P2 runs for 3 units (remaining time 1)
Time 6-9: P3 runs for 3 units (remaining time 3)
Time 9-10: P4 runs for 2 units (remaining time 0, complete)
Time 10-12: P1 runs for 2 units (remaining time 0, complete)
Time 12-13: P2 runs for 1 unit (remaining time 0, complete)
Time 13-15: P3 runs for 3 units (remaining time 0, complete)

Calculate Turnaround and Waiting Times

Turnaround Time (TAT) = Completion Time – Arrival Time
Waiting Time (WT) = Turnaround Time – Burst Time

P1:

Completion Time = 12

Turnaround Time = 12 – 0 = 12

Waiting Time = 12 – 5 = 7

P2:

Completion Time = 13

Turnaround Time = 13 – 1 = 12

Waiting Time = 12 – 4 = 8

P3:

Completion Time = 15

Turnaround Time = 15 – 2 = 13

Waiting Time = 13 – 6 = 7

P4:

Completion Time = 10

Turnaround Time = 10 – 3 = 7

Waiting Time = 7 – 2 = 5

Summary

Process ID	Arrival Time	Burst Time	Completion Time	Turnaround Time	Waiting Time
P1	0	5	12	12	7
P2	1	4	13	12	8
P3	2	6	15	13	7
P4	3	2	10	7	5

Average Times

Average Turnaround Time = (12 + 12 + 13 + 7) / 4 = 44 / 4 = 11.0
Average Waiting Time = (7 + 8 + 7 + 5) / 4 = 27 / 4 = 6.75

Output

Process | Turnaround Time | Waiting Time
P1 | 12 | 7
P2 | 12 | 8
P3 | 13 | 7
P4 | 7 | 5

Average Waiting Time= 6.75
Average Turnaround Time = 11.0

Question 2:

Consider the following set of processes that arrive at different times. Calculate the average waiting time and average turnaround time using Round Robin scheduling with a time quantum of 4 units.

Process ID	Arrival Time	Burst Time
P1	0	7
P2	2	4
P3	4	1
P4	5	4
P5	6	6

Steps to Solve

Construct the Gantt Chart:
- Process the tasks in order of their arrival and given burst times.
Track remaining times and process scheduling:
- P1: Remaining time 7
- P2: Remaining time 4
- P3: Remaining time 1
- P4: Remaining time 4
- P5: Remaining time 6

Gantt Chart Construction

Using a time quantum of 4 units:

Time 0-4: P1 runs for 4 units (remaining time 3)
Time 4-8: P2 runs for 4 units (remaining time 0, complete)
Time 8-9: P3 runs for 1 unit (remaining time 0, complete)
Time 9-13: P4 runs for 4 units (remaining time 0, complete)
Time 13-17: P5 runs for 4 units (remaining time 2)
Time 17-20: P1 runs for 3 units (remaining time 0, complete)
Time 20-22: P5 runs for 2 units (remaining time 0, complete)

Calculate Turnaround and Waiting Times

Turnaround Time (TAT) = Completion Time – Arrival Time
Waiting Time (WT) = Turnaround Time – Burst Time

P1:

Completion Time = 20

Turnaround Time = 20 – 0 = 20

Waiting Time = 20 – 7 = 13

P2:

Completion Time = 8

Turnaround Time = 8 – 2 = 6

Waiting Time = 6 – 4 = 2

P3:

Completion Time = 9

Turnaround Time = 9 – 4 = 5

Waiting Time = 5 – 1 = 4

P4:

Completion Time = 13

Turnaround Time = 13 – 5 = 8

Waiting Time = 8 – 4 = 4

P5:

Completion Time = 22

Turnaround Time = 22 – 6 = 16

Waiting Time = 16 – 6 = 10

Summary

Process ID	Arrival Time	Burst Time	Completion Time	Turnaround Time	Waiting Time
P1	0	7	20	20	13
P2	2	4	8	6	2
P3	4	1	9	5	4
P4	5	4	13	8	4
P5	6	6	22	16	10

Average Times

Average Turnaround Time = (20 + 6 + 5 + 8 + 16) / 5 = 55 / 5 = 11.0
Average Waiting Time = (13 + 2 + 4 + 4 + 10) / 5 = 33 / 5 = 6.6

Output

Process | Turnaround Time | Waiting Time
P1      | 20              | 13
P2      | 6               | 2
P3      | 5               | 4
P4      | 8               | 4
P5      | 16              | 10

Average Waiting Time= 6.6
Average Turnaround Time = 11.0