the page fault rate, defined as the ratio of number of page faults to the number of memory accesses is _____________.
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Answer: 0.6
To find the page fault rate, we trace the Least Recently Used (LRU) page replacement policy with 4 initially empty page frames.
The step-by-step memory state transition for the reference string is shown below:
| Access | 7 | 2 | 7 | 3 | 2 | 5 | 3 | 4 | 6 | 7 | 7 | 1 | 5 | 6 | 1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frame 1 | 7 | 7 | 7 | 7 | 7 | 7 | 7 | 4 | 4 | 4 | 4 | 4 | 5 | 5 | 5 |
| Frame 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| Frame 3 | 3 | 3 | 3 | 3 | 3 | 3 | 7 | 7 | 7 | 7 | 7 | 7 | |||
| Frame 4 | 5 | 5 | 5 | 5 | 5 | 5 | 1 | 1 | 1 | 1 | |||||
| Fault? | F | F | H | F | H | F | H | F | F | F | H | F | F | H | H |
From the trace:
- Total number of memory accesses =
- Total number of page faults (F) =
The page fault rate is calculated as:
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