Associative Caches

Associative Caches

-Increased associativity decrease miss rate but with diminishing returns


Spectrum of associativity

Type of associative

1. Fully Associative
--In a fully associative scheme, any slot can store the cache line. The hardware for finding whether the desired data is in the cache requires comparing the tag bits of the address to the tag bits of every slot (in parallel), and making sure the valid bit is set.

2. Set associative
--A set-associative cache scheme is a combination of fully associative and direct mapped schemes. You group slots into sets. You find the appropriate set for a given address (which is like the direct mapped scheme), and within the set you find the appropriate slot (which is like the fully associative scheme).

Example

--Compare 4-blocks caches with block access sequence: 0,8,0,6,8