The GATE Grind

GATE 2018 CS – Question 20

Operating System · Memory Management and Virtual Memory · 1 mark · Multiple choice

Consider a process executing on an operating system that uses demand paging. The average time for a memory access in the system 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?

  1. $(D-M)/(X-M)$
  2. $(X-M)/(D-M)$
  3. $(D-X)/(D-M)$
  4. $(X-M)/(D-X)$

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Correct answer: (B) $(X-M)/(D-M)$

Explanation

With page fault rate $p$, $X=(1-p)M+pD=M+p(D-M)$, so $p=\frac{X-M}{D-M}$.