Source : Free On-Line Dictionary of Computing

sector mapping
     
        In this scheme the memory and {cache} are divided into blocks
        of 2^m bytes (the {cache line} size).  A sector consists of
        2^n consecutive blocks.
     
        When a block is cached, it is read into the correct position
        in any sector of the cache, given by discarding the bottom m
        address bits and taking the next n as the block number within
        the sector.
     
        That whole sector is then tagged with the remaining upper
        address bits and the other blocks in the sector are marked as
        invalid.  This scheme takes advantage of locality of reference
        to consecutive blocks and needs fewer tags thus reducing the
        cost of associative access to the tags.