partition number, and 'part2' and 'part3' are both zero.
As another example, if a disk is partitioned first into DOS partitions, and
then one of those DOS partitions is subdivided into several BSD partitions
using BSD's "disklabel" strategy, then 'part1' contains the DOS partition
number, 'part2' contains the BSD sub-partition within that DOS partition,
and 'part3' is 0xFF.<P>

DOS extended partitions are indicated as partition numbers starting from 4
and increasing, rather than as nested sub-partitions, ev