Source : Free On-Line Dictionary of Computing

direct mapped cache
     
         A {cache} where the cache location for a given
        address is determined from the middle address bits.  If the
        {cache line} size is 2^n then the bottom n address bits
        correspond to an offset within a cache entry.  If the cache
        can hold 2^m entries then the next m address bits give the
        cache location.  The remaining top address bits are stored as
        a "tag" along with the entry.
     
        In this scheme, there is no choice of which block to flush on
        a cache miss since there is only one place for any block to
        go.  This simple scheme has the disadvantage that if the
        program alternately accesses different addresses which map to
        the same cache location then it will suffer a cache miss on
        every access to these locations.  This kind of {cache
        conflict} is quite likely on a multi-processor.  See also
        {fully associative cache}, {set associative cache}.