GATE CS 2021 Set 1 — Question 35
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Operating System → Process Scheduling → FCFS & SJF
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Question
Three processes arrive at time zero with CPU bursts of 16, 20 and 10 milliseconds. If the scheduler has prior knowledge about the length of the CPU bursts, the minimum achievable average waiting time for these three processes in a non-preemptive scheduler (rounded to nearest integer) is ________ milliseconds.
Correct answer
12 to 12
Solution
To minimize the average waiting time in a non-preemptive scheduler, the Shortest Job First (SJF) scheduling algorithm is optimal.Given CPU bursts: ms, ms, ms.Order of execution (SJF):
1. (10 ms)
2. (16 ms)
3. (20 ms)
Waiting times:- starts at 0. Waiting time ms.
- starts after finishes (at 10). Waiting time ms.
- starts after finishes (at ). Waiting time ms.
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