ITPEC FE Morning October 2021 Question 17
ITPEC FE Morning October 2021 — Question 17 of 80
Round Robin Scheduling — calculate average waiting time with a fixed time quantum.
Given processes P1=10, P2=23, P3=7, P4=3 with time quantum=10 ms, all arriving at time 0:
Simulation:
- 0–10: P1 runs 10 → done
- 10–20: P2 runs 10 → 13 left
- 20–27: P3 runs 7 → done
- 27–30: P4 runs 3 → done
- 30–40: P2 runs 10 → 3 left
- 40–43: P2 runs 3 → done
Waiting time = completion − arrival − CPU time:
- P1: 10 − 0 − 10 = 0
- P2: 43 − 0 − 23 = 20
- P3: 27 − 0 − 7 = 20
- P4: 30 − 0 − 3 = 27
Average = (0 + 20 + 20 + 27) / 4 = 67 / 4 = 16.75
Why not others:
- (a) 10.75 — underestimates waiting for later processes
- (b) 14.25 — likely a miscalculation of queue order
- (c) 15.00 — does not match the simulation
Key rule: Waiting time = completion_time − arrival_time − CPU_execution_time. Simulate each quantum step carefully; processes finishing early release CPU immediately.
AI-generated — may contain errors
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