Consider a set of 5 processes whose arrival time. CPU time needed and the priority are given below
| Process Priority | Arrival Time (in ms) | CPU Time Needed (in ms) | Priority |
| P1 | 0 | 10 | 5 |
| P2 | 0 | 5 | 2 |
| P3 | 2 | 3 | 1 |
| P4 | 5 | 20 | 4 |
| P5 | 10 | 2 | 3 |
smaller the number, higher the priority.
If the CPU scheduling policy is priority sche duling with pre-emption, the average waiting time will be
| A. | 19 ms |
| B. | 7.6 ms |
| C. | 6.8 ms |
| D. | none of these |
Answer : B Explanation : Here the process which will start at the initial millisecond will be P2 as it has more priority that P1. ms Process 0 to 2 P2 (P2 completed 2 ms here) 2 to 5 P3 (No wait for P3) 5 to 8 P2 (P2 had to wait 3 ms to get executed ) 8 to 10 P4 (P4 had to wait 3 ms to get started) 10 to 12 P5 (No wait for P5) 12 to 30 P4 (P4 had to wait 2 ms to complete its remaining) 30 to 40 P1 (Was waiting for 30 ms) So, waiting time---- P1 -30 P2 -3 P3 -0 P4 -5 P5 -0 Average---- (30+3+0+5+0)/5= 7.6 ms . |
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Option: A Explanation : Explanation will come here. Explanation will come here. Explanation will come here. Explanation will come here. Explanation will come here. |
