co cache memory

Question

if there is a miss in cache and hit in mm what is access time 60ns or 60+20=80ns.

how is the statement " reference started again" related to the  meaning of the question?

Comments

"Reference started again" simply means that the data will be again accessed next time and thus, for the Miss penalty time, we need to take into account only till the data is moved into the cache from main memory.

Answer 1

Since nothing is mentioned, I would assume Hierarchical access.

T_avg = H₁T₁ + (1-H₁)H₂(T₁+T₂) + (1-H₁)(1-H₂)(T₁+T₂+T₃)

Since there are 3 levels. 

This formula can be interpreted as

[(Hit in Level 1) * (Time to access in level 1)] + [(Miss in Level 1) *  (Hit in Level 2) * (Time to access Level 1 memory + Time to access Level 2 memory)] + [(Miss in Level 1) * (Miss in Level 2) * (Time to access Level 1 memory + Time to access Level 2 memory + Time to access Level 3 memory)]

In the last term, H₃ is assumed to be 1 as the word has to be there in the last level memory.

Thus in this case,

H₁ = 0.9

H₂ = 0.6

T₁ = 20

T₂ = 60

T₃ = 12 * 10⁶ ns

So, Tavg = 480,026 ns