Consider three CPU-intensive processes, which require 10,20 and 30 time units…
2006
Consider three CPU-intensive processes, which require 10,20 and 30 time units and arrive at times 0,2 and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end.
- A.
1
- B.
2
- C.
3
- D.
4
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Correct answer: B
Under Shortest Remaining Time First (SRTF) scheduling, we track the remaining time of each process.
1. T=0: P1 arrives (10 units). Runs. 2. T=2: P2 arrives (20 units). P1 rem 8 < P2 rem 20. P1 continues. 3. T=6: P3 arrives (30 units). P1 rem 4 < P3 rem 30. P1 continues. 4. T=10: P1 finishes. Switch to P2 (Switch 1). 5. T=30: P2 finishes (ran for 20 units). Switch to P3 (Switch 2). 6. T=60: P3 finishes.
Excluding start and end, total context switches = 2.
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