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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 experimental 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?

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 experimental 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? Correct Answer (X - M) / (D - M)

Let P be the page fault rate.

Average memory access time = ( 1 - page fault rate) × memory access time when no page fault  +  Page fault rate × Memory access time when page fault.

X = (1 - P) × M + P × D

∴X = M - PM + PD

X - M = P(D - M )

P = (X - M)/( D - M)

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