Source : Free On-Line Dictionary of Computing

set associative cache
     
         A compromise between a {direct mapped cache}
        and a {fully associative cache} where each address is mapped
        to a certain set of cache locations.  The address space is
        divided into blocks of 2^m bytes (the {cache line} size),
        discarding the bottom m address bits.  An "n-way set
        associative" cache with S sets has n cache locations in each
        set.  Block b is mapped to set "b mod S" and may be stored in
        any of the n locations in that set with its upper address bits
        as a tag.  To determine whether block b is in the cache, set
        "b mod S" is searched associatively for the tag.
     
        A direct mapped cache could be described as "one-way set
        associative", i.e. one location in each set whereas a fully
        associative cache is N-way associative (where N is the total
        number of blocks in the cache).  Performance studies have
        shown that it is generally more effective to increase the
        number of entries rathethe r than associativity and that 2- to
        16-way set associative caches perform almost as well as fully
        associative caches at little extra cost over direct mapping.
     
        (2002-02-09)