If the disk was formatted by DOS 4.0 or later, use INT 21: AX=6900 gets
 the serial number; AX=6901 sets it. (The disk serial number doesn't
 exist if the disk was formatted with an earlier version of DOS, or with
 some third-party formatters.) See Ralf Brown's interrupt list (<Q:02.03>
 [What and where is Ralf Brown's interrupt list?]), or PC Magazine July
 1992 (xi:13) page 496, for details.

 INT 21 AH=69 also gets and sets the volume label in the boot record,
 which is not necessarily the same as "the" volume label displayed by the
 DIR, VOL, and LABEL commands. For that volume label, see <Q:05.12> [How
 can I read, create, change, or delete the volume label?]

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