Question

Let the page fault service time be 10 ms in a computer with average memory access time being 20ns. If one page fault is generated for every ${10}^6$ memory accesses, what is the effective access time for the memory?

• A. 30 ns
• B. 21 ns
• C. 23 ns
• D. 35 ns

Answer 1

The correct option is A 30 ns

Effective access time = [(1 - p)* access time when no page fault +p* access time during page fault]

$=[1-\left(\frac{1}{{10}^6}\right)]\ast 20ns+\left(\frac{1}{{10}^6}\right)\ast 10$ ms
$=\left(\frac{{10}^6-1}{{10}^6}\right)\ast 20ns+\left(\frac{1}{{10}^6}\right)\ast 10\ast {10}^{6}ns\approx 30$ ns