Cache placement policies

Cache placement policies are policies that determine where a particular memory block can be placed when it goes into a CPU cache. A block of memory cannot necessarily be placed at an arbitrary location in the cache; it may be restricted to a particular cache line or a set of cache lines by the cache's placement policy.

There are three different policies available for placement of a memory block in the cache: direct-mapped, fully associative, and set-associative. Originally this space of cache organizations was described using the term "congruence mapping".