Let the page fault service time be 10 milliseconds(ms) in a computer with…
2011
Let the page fault service time be 10 milliseconds(ms) in a computer with average memory access time being 20 nanoseconds (ns). If one page fault is generated every 10^6 memory accesses, what is the effective access time for memory?
Answer: B. 30 ns — Key idea: compute the effective access time by weighting the normal memory access time and the page-fault service time by their probabilities. Step 1: Fault…
- A.
21 ns
- B.
30 ns
- C.
23 ns
- D.
35 ns
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Correct answer: B
Key idea: compute the effective access time by weighting the normal memory access time and the page-fault service time by their probabilities.
Step 1: Fault rate p = 1 / 1,000,000 = 1e-6.
Step 2: Convert page-fault service time to nanoseconds: 10 ms = 10 × 10^6 ns = 10,000,000 ns.
Step 3: Use the formula EAT = (1 − p) × memory_access_time + p × page_fault_service_time.
Step 4: Plug in values: EAT = (1 − 1e-6) × 20 ns + 1e-6 × 10,000,000 ns = 20 − 0.00002 + 10 = 29.99998 ns.
Conclusion: The effective access time is approximately 30 ns.
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