Operating Systems
Spot it
Spot the FCFS scheduling mistake
Can you spot the mistake in this FCFS waiting time answer?
Quick check · tap an answer to continue
Lesson notes
Key points
- Processes run in arrival order: P1, then P2, then P3.
- P1 waits 0 ms, P2 waits 3 ms, P3 waits 6 ms.
- Total waiting time is 0 plus 24 plus 27, which is 51 ms.
- Average waiting time is 51 divided by 3, which is 17 ms.
Takeaway: In FCFS, each wait equals the sum of earlier bursts.
Quick check: Which step is wrong?
- Step 1
- Step 2
- Step 3
P2 must wait for all of P1's 24 ms burst, not P3's burst; waits are not 3 and 6.
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