Round Robin scheduling Exercise with solution

By: Prof. Dr. Fazal Rehman | Last updated: July 28, 2024

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.

Steps to Solve

1. Construct the Gantt Chart:
   • Process the tasks in order of their arrival and given burst times.
2. 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

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

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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.

Steps to Solve

1. Construct the Gantt Chart:
   • Process the tasks in order of their arrival and given burst times.
2. 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

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