The line size must be a power of two. If the line is four words, bits 2 through 7 of the memory address specify the cache line. A computer has a cache, main memory, and a disk used for virtual memory. The cache-hit ratio is 0.9 and the main memory hit ratio is 0.6. Cache reference is 20 ns.
Weighted average is sum of category percentage times category value.
The disk access time dominates this system. Need to up the main memory hit rate.