INT 21 - DOS 3.2+ - IOCTL - SET LOGICAL DRIVE MAP
AX = 440Fh
BL = physical drive number (00h=default,01h=A:,etc))
Return: CF set on error
AX = error code (01h,0Fh) (see AH=59h)
CF clear if successful
drive now responds to next logical drive number
Note:   maps logical drives to physical drives, similar to DOS's treatment of
a single physical floppy drive as both A: and B:
SeeAlso: INT 2F/AX=122Bh

See also: 21440E

21440F - DOS 3.2+ - IOCTL - SET LOGICAL DRIVE MAP