A memory cache, sometimes called a cache store or RAM cache, is a portion of mem

Question

A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.

Consider two alternate caches, each with four sectors holding one block per sector and one 32-bit word per block. One cache is direct mapped, and the other is fully associative with least recently used (LRU) replacement policy. The machine is byte addressed on word boundaries and uses write allocation with write back.

What would the overall miss ratio be for the following address stream on the direct mapped cache? Assume the cache starts out completely invalidated.

read 0x00
read 0x04
write 0x08
read 0x10
read 0x08
write 0x00

Explanation / Answer

To calculate cache miss ratio, we first calculate cache hit ratio

HIT Ratio=( No. of hits/Total accesses)*100

=(2/6)*100

=100/3

=33.33

Miss ratio=( No. of miss/Total accesses)*100

=(4/6)*100

=66.66

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