Consider a paging system where translation look aside buffer (TLB) a special…
2019
Consider a paging system where translation look aside buffer (TLB) a special type of associative memory is used with hit ratio of 80%.
Assume that memory reference takes 80 nanoseconds and reference time to TLB is 20 nanoseconds. What will be the effective memory access time given 80% hit ratio?
- A.
110 nanoseconds
- B.
116 nanoseconds
- C.
200 nanoseconds
- D.
100 nanoseconds
Attempted by 130 students.
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Correct answer: B
Solution summary: compute the effective memory access time using TLB hit and miss scenarios.
Given: TLB hit ratio = 0.8, TLB access time = 20 ns, memory access time = 80 ns.
On a TLB hit: time = TLB access + one memory access = 20 + 80 = 100 ns.
On a TLB miss: time = TLB access + memory access to read page table + memory access to read data = 20 + 2×80 = 180 ns.
Effective memory access time = (hit ratio)×(hit time) + (miss ratio)×(miss time) = 0.8×100 + 0.2×180 = 116 ns.
Answer: 116 nanoseconds
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