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