7.4a Average Memory Access Time

Average Memory Access Time

The Average (Expected) Memory Access Time is the average time it takes to access a memory location, considering both cache hits and cache misses. It is given by the formula:
${\text{AMAT}}_i=T_{H_i}+M_i\cdot {\text{AMAT}}_{i+1},$
where for the $i$-th cache level s.t. $i\in \{1,2,\cdots ,n\}$, $T_{H_i}$ is its hit time (the time it takes to check the cache), and $M_i$ is its miss rate. Then, ${\text{AMAT}}_{i+1}$ can be regarded as the miss penalty for cache $i$, where ${\text{AMAT}}_{n+1}$ is the time it takes to access memory after the $n$-th cache performs a miss.

Intuition