Question

If a cache memory has a hit rate of 75 percent, memory request take l2ns to complete if they hit in the cache and memory request that miss in the cache take 100 ns to complete, what is the average access time of cache? ​

Answer 1

Answer:

given the main memory access time when the cache miss is =100ns

cache access time=10ns

and hit rate is =75%=0.75

there are 2 ways to find out memory access time

case1 : both cache and memory accessed simultaneously

then avg memory access time= (hit rate*cache access time)+(miss rate*main memory access time)

=(0.75*10)+((1-0.75)*100)=32.5ns

case 2: both cache and memory accessed serially

then avg memory access time=(hit rate*cache access time)+(miss rate*(cache access time+main memory access time)

=(0.75*10)+(0.25*(10+100))

=35ns