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
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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