Given memory access time as p nanoseconds and additional q nanoseconds for…
2021
Given memory access time as p nanoseconds and additional q nanoseconds for handling the page fault. What is the effective memory access time if a page fault occurs once for every 100 instructions? [
- A.
\(P + \frac {q} {100}\) - B.
\(\frac {p+q} {100}\) - C.
\(p + q\) - D.
\(\frac {p} {100} + q\)
Attempted by 190 students.
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Correct answer: A
Key insight: page fault probability = 1/100; when no fault time = p; when fault time = p + q.
Probability of a page fault per instruction = 1/100. Probability of no page fault = 99/100.
If no page fault occurs, memory access time = p.
If a page fault occurs, memory access time = p + q.
Expected (effective) memory access time = (99/100)*p + (1/100)*(p + q) = p + q/100.
Final answer: Effective memory access time = p + q/100 nanoseconds.
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