Here is the Question :

The hit ratio is the percentage of times that a page number is found in the Translation look-aside buffer (TLB). An 80% hit ratio means that we find the desired page number in the TLB 80% of the time. Suppose we have a hit ratio of 70% and 40 ns is needed for TLB, where main memory access time is 80 ns. Calculate the EAT (effective access time)

I found many formula I'm kinda lost with this Question

The first formula

EAT = (Hit ratio * Hit time) + (Miss ratio * Miss penalty)

the second formula EAT = TLB + (2 – hit ratio) * main memory access

the third formula

EAT = Hit Ratio* TLB Access Time + Miss Ratio* (TLB Access Time + Main Memory Access Time)

I appreciate the help for guide thought the correct one


1 Answer 1


Assume that you perform 100 accesses. 70 of them will take 40 ns and 30 of them 40+80 ns. On average 64 ns.

Can you derive the formula from this ? (Or compare to the results with the given formulas.)


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