If a cache hit retrieves a value in 5ns, and retrieving a value from main memory requires 25ns, what is the average effective access time for this cache, assuming that all memory accesses exhibit the same hit rate of 0.8 and assuming the system uses a) A non-overlapped (sequential) access strategy

10 ns

Explanation:

Determine the average effective access time for the Cache

Average effective access time for Non-overlapped access strategy

= ( Hit Rate * Cache Hit Time) + ( 1 - Hit Rate ) * ( Main Memory Access Time + Cache Hit Time )   ( 1 )

Given that : Hit Rate = 0.8 , Cache Hit time = 5ns , Main Memory access time = 25ns ,  

Equation 1 becomes

= ( 0.8 * 5 ) + ( 1 - 0.8 ) * (25 + 5)

= 4 + 0.2 * 30 =  4 + 6 = 10ns