qCluster

                       cluster
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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.
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■ 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.