cluster
                                                     
A cluster, as used in the DOS file system, is a group
of sequential sectors on disk.

Each cluster represents a power-of-2 count of sectors.
Common cluster sizes are 2, 4, 8, and 16 sectors.
                                                     
  DOS allocates disk data in clusters in the FAT.
  DOS fn 1cH returns cluster size for a disk.
  A disk Boot sector contains the cluster size.

qCluster