We have a system which supports 2 level of hierarchical memory organization and has the following specification:

Find out the average access time.

(A) 120 ns
(B) 124 ns
(C) 126 ns
(D) 130 ns


Answer: (D)

Explanation: L₁ access time T₁ = 10ns
L₂ access time T₂ = 50 * 6 = 300(Because block size is 6 word)
Miss ratio for L₁ is 40 %
I.e.Complementary H₁ = 0.6
Miss ratio for highest level is always 0.
I.e Complementary H₂ = 1
T_Avg = H₁T₁ + (1 -H₁) * H₂ *(T₁ + T₂)
= 0.6 * 10 + 0.4 * 1 * ( 10 + 300 )
= 6 + 124
= 130 ns
Option (D) is correct.


Quiz of this Question