Suppose for a process 𝑃, reference to pages in order are 1,2,4,5,2,1,2,4.…

2018

Suppose for a process 𝑃, reference to pages in order are 1,2,4,5,2,1,2,4. Assume that main memory can accomodate 3 pages and the main memory has already 1 and 2 in the order 1 – first, 2 – second. At this moment, assume FIFO Page Replacement Algorithm is used then the number of page faults that occur to complete the execution of process 𝑃 is

  1. A.

    4

  2. B.

    3

  3. C.

    5

  4. D.

    6

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Correct answer: C

Solution: Simulate the FIFO algorithm with three frames. Initial frames: page 1 (oldest), page 2 (second), and one empty frame.

  1. Reference 1: Hit (page 1 is already in memory). Frames: [1, 2, empty]. Faults so far: 0.

  2. Reference 2: Hit (page 2 is in memory). Frames unchanged: [1, 2, empty]. Faults so far: 0.

  3. Reference 4: Miss. Load into the empty frame. Frames: [1, 2, 4]. Faults so far: 1.

  4. Reference 5: Miss. FIFO evicts the oldest loaded page (page 1). Replace it with 5. Frames: [5, 2, 4]. Faults so far: 2.

  5. Reference 2: Hit (page 2 is present). Frames unchanged: [5, 2, 4]. Faults so far: 2.

  6. Reference 1: Miss. FIFO evicts the oldest remaining page (page 2). Replace it with 1. Frames: [5, 1, 4]. Faults so far: 3.

  7. Reference 2: Miss. FIFO evicts the oldest page (page 4). Replace it with 2. Frames: [5, 1, 2]. Faults so far: 4.

  8. Reference 4: Miss. FIFO evicts the oldest page (page 5). Replace it with 4. Frames: [4, 1, 2]. Faults so far: 5.

Total page faults: 5

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