What is the average access time for a system which supports 2 level of hierarchical memory organization and has the following specification.



Given access time per word.
(A) 120 ns
(B) 124 ns
(C) 126 ns
(D) 130 ns


Answer: (D)

Explanation: L₁ access time T₁ = 10 ns
L₂ access time = 50
L₂ access time T₂ = 50*6 (given block is 6 word) = 300 ns.

Now, hit ratio of L₁

= 100% - 40% 
= 60% 
= 0.6 

And, miss ratio for highest level is always 0. Hit ratio of L₂

= 100% - 0% 
= 100% 
= 1 

Therefore, T_Avg

= H1T1 + (1 -H1) * H2 *(T1 + T2)
= 0.6 * 10 + 0.4 * 1 * (10 + 300)
= 6 + 124
= 130 ns 

So, option (D) is correct.


Quiz of this Question