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.