Consider main memory of size 32GB and blocks of size 32KB. If the propagation delay of comparator is 10T ns (T is the number of tag bits) and the propagation delay of OR gate is 10 ns. What will be the Hit Latency in ns. ?

Answer hidden

Habib Mohammad Khan @habibkhan
8 Dec 2016 07:08 pm

First of all we find no of tag bits which is given by :

Main memory size / Block size  = 32 GB / 32 KB  =  220 ..As no mapping constraint is given we have assumed that main memory block may go to any of the cache line and hence fully associative assumption..

So no of tag bits = log2 220   =  20 bits

So delay due to tag comparator  = 10T = 200 ns 

And propogation delay of OR gate = 10 ns

Hence hit latency  = 200 + 10  = 210 ns

Hence 210 is the correct answer..

PratikS @pratikshende
9 Dec 2016 02:57 pm

for associate mapping we doesnt use any mux .so why we are adding propogation delay of or gate .correct ans has to be 200ns . in case of set associate we use mux ..