We have
Ts = average (system) access time
T1 = access time of M1 (e.g. cache)
T2 = access time of M2 (e.g. main memory)
T3 = access time of M3 (e.g. disk)
H1 = hit ratio, fraction of time reference is found in M1
H2 = hit ratio, fraction of time reference is found in M2
The average time to access an item in case the item in cache is:
Select one of the following: