Determine the number of page faults when references to pages occur in the…

2016

Determine the number of page faults when references to pages occur in the following order: 1, 2, 4, 5, 2, 1, 2, 4 Assume that the main memory can accommodate 3 pages and the main memory already has the pages 1 and 2, with page one having brought earlier than page 2. (LRU page replacement algorithm is used)

  1. A.

    3

  2. B.

    5

  3. C.

    4

  4. D.

    None of these

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Correct answer: C

We simulate the LRU page replacement algorithm with 3 frames.

Initial state: Memory contains pages 1 and 2. Page 1 is older than Page 2. One frame is empty.

Reference 1: Hit (already in memory). Memory state updates to [2, 1].

Reference 2: Hit (already in memory). Memory state updates to [1, 2].

Reference 4: Page Fault (empty frame available). Memory state becomes [1, 2, 4]. Total faults: 1.

Reference 5: Page Fault (replace LRU page 1). Memory state becomes [2, 4, 5]. Total faults: 2.

Reference 2: Hit (already in memory). Memory state updates to [4, 5, 2].

Reference 1: Page Fault (replace LRU page 4). Memory state becomes [5, 2, 1]. Total faults: 3.

Reference 2: Hit (already in memory). Memory state updates to [5, 1, 2].

Reference 4: Page Fault (replace LRU page 5). Memory state becomes [1, 2, 4]. Total faults: 4.

Total page faults: 4.

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