In a paging system, it takes 30 ns to search translation Look-a-side buffer (TLB) and 90 ns to access the main memory. If the TLB hit ratio is 70%, the…
In a paging system, it takes 30 ns to search translation Look-a-side buffer (TLB) and 90 ns to access the main memory. If the TLB hit ratio is 70%, the effective memory access time is :
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Correct answer: (B) 147ns
Explanation
TLB hit ratio 70%, TLB search 30 ns, memory access 90 ns. On a hit, the page is found in the TLB (30 ns); on a miss, the TLB is searched and the page table read from memory (30 + 90 ns); then 90 ns to access the data. Total = (0.7 × 30) + (0.3 × (90 + 30)) + 90 = 21 + 36 + 90 = 147 ns