Determine Access time of system

Question

If Cache access time is 10 ns . main memory access time is 150 ns. Cache hit rate is 99%.

Determine effective access time of system.

Answer 1

Cache access time is 10 ns

main memory access time is 150 ns.

Cache hit rate is 99% i.e 0.99

To Determine effective access time of system: first we see in cache if it is not found in cache then we look in main memory.

Effective memory access time=0.99*10+0.01*(10+150)=9.9+1.6=11.5 ns

Answer 2

By default cache access is hierarchical

so EMAT $= 10 + 0,01 *150 = 11.5ns$

If we assume its simultaneous access

EMAT $= 0.99*10 + 0.01 * 150 = 11.4ns $