Operating Systems · Question 14 · Hard
Operating Systems question 14
A TLB lookup takes 20 ns and a main-memory access takes 100 ns. On a TLB miss, one extra memory access is needed to read the page table. If the TLB hit ratio is 80%, what is the effective memory access time?
- 140 ns
- 120 ns
- 160 ns
- 136 ns
Answer and explanation
Answer: A. 140 ns
Explanation: A hit costs 20 + 100 = 120 ns and a miss costs 20 + 100 + 100 = 220 ns. EAT = 0.8 × 120 + 0.2 × 220 = 96 + 44 = 140 ns.
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