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Operating Systems
Memory Management
GATE 2018
Medium

Consider a process executing on an operating system that uses demand paging. The average time for a memory access is M units if the corresponding memory page is available in memory, and D units if the memory access causes a page fault. It has been experimentally measured that the average time taken for a memory access in the process is X units. Which one of the following is the correct expression for the page fault rate experienced by the process?

  • A(D − M) / (X − M)
  • (X − M) / (D − M)
  • C(D − X) / (D − M)
  • D(X − M) / (D − X)

Explanation

Let p be the page-fault rate. The average access time is a weighted average: X = (1−p)·M + p·D = M + p(D−M). Solving for p: p = (X−M)/(D−M).

Source: GATE CS 2018 (2018)

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