What is ....

[Collins Richey]

One common use of bit maps is in the maintenance of a cache or storage
pages.  The presence or absence of a cache or storage page is easily
calculated by the byte+bit distance into the bit map, and the use of
pages is turned on/off by logical operations on the appropriate byte
or bytes.

--
Collins Richey
      Debugging is twice as hard as writing the code ... If you write
      the code as cleverly as possible, you are, by definition, not
      smart enough to debug it.
             -Brian Kernighan