Question

Let the page fault service time be 10 millisecond(ms) in a computer with average memory access time being 20 nanosecond(ns). If one page fault is generated for every 106 memory accesses, what is the effective access time for memory ?
(A) 21 ns
(B) 23 ns
(C) 30 ns
(D) 35 ns

Answer 1

Answer on Question#38079 – Math - Other

Let $r$ be the page fault rate, $t$ be the page fault service time, $\tau$ be the memory access time.

Then the effective memory access time:

$$M = r \cdot t + (1 - r) \cdot \tau = \frac {1}{10^{6}} \cdot 10 \cdot 10^{-3} \cdot 10^{9} \text{ ns} + \left(1 - \frac {1}{10^{6}}\right) \cdot 20 \text{ ns} \approx 10 \text{ ns} + 20 \text{ ns} = 30 \text{ ns}$$

Answer: (C) 30 ns.