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GATE 2011 CS (CS1) – Question 30

Operating System · Memory Management and Virtual Memory · 1 mark · Multiple choice

Page-fault service time is 10 ms; normal memory access is 20 ns. One fault occurs per 10⁶ accesses. Find effective access time.

  1. 21 ns
  2. 30 ns
  3. 23 ns
  4. 35 ns

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Show answer and explanation

Correct answer: (B) 30 ns

Explanation

Fault probability is 10⁻⁶. The extra mean fault cost is 10⁻⁶×10 ms=10 ns. Adding ordinary 20 ns gives approximately 30 ns, B. Weighting the ordinary access by 1−10⁻⁶ changes only a negligible fraction of a nanosecond.

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