A paging scheme uses a Translation Look-aside Buffer (TLB). A TLB-access takes…
2008
A paging scheme uses a Translation Look-aside Buffer (TLB). A TLB-access takes 10 ns and a main memory access takes 50 ns. What is the effective access time(in ns) if the TLB hit ratio is 90% and there is no page-fault?
- A.
54
- B.
60
- C.
65
- D.
75
Attempted by 204 students.
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Correct answer: C
Solution: compute the effective access time (EAT) using hit and miss costs.
TLB access time = 10 ns; main memory access = 50 ns.
Time on TLB hit = TLB access + one memory access = 10 + 50 = 60 ns.
Time on TLB miss (no page fault) = TLB access + memory access for page table + memory access for data = 10 + 50 + 50 = 110 ns.
Hit ratio = 0.9, miss ratio = 0.1. EAT = 0.9 * 60 + 0.1 * 110 = 54 + 11 = 65 ns.
Answer: 65 ns.