ISRO | ISRO CS 2016 | Question 19

Let the page fault service time be 10 ms in a computer with average memory access time being 20 ns. If one page fault is generated for every
10⁶ memory accesses, what is the effective access time for the memory?
(A) 21.4 ns
(B) 29.9 ns
(C) 23.5 ns
(D) 35.1 ns

Answer: (B)
Explanation: page fault service time, PFST = 10 ms = 10⁷ ns
page fault frequency, PFF = 1/(10⁶) = 10^-6
memory access time, tm = 20 ns
effective access time = PFF * PFST + (1-PFF) * tm = 10^-6 * 10 + (0.999999) * 20 = 29.9 ns
So, option (B) is correct.
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