DOCUMENT ID:  1328-02

SYNOPSIS:     A description of Cache & Cache Hit Rate

OS RELEASE:   2.4

PRODUCT:      Solaris

KEYWORDS:     cache hit rate memory


DESCRIPTION:

Description of Cache & Cache Hit Rate


                        CACHE & CACHE HIT RATE


Cache:

  Cache is not used as the exclusive memory on the system because:

 * It is expensive.

 * It takes up more physical space.

 * It consumes more power.

 * There is a "point of diminishing returns".

The density (amount of data that can be stored on the chip) of SRAM is
much less.  The amount of current drawn by the chip is greater than that
necessary to power DRAM chips.


Cache Hit Rate:

The cache hit rate is the percentage of memory accesses that result in
finding the data in cache. 

The cache hit rate depends on:

 * Size of cache

 * Fetch rate

 * Locality of reference


The fetch rate is the number of bits in cache for each memory access.


DATE APPROVED: 05/08/95