Function 440Fh (68-15)   IOCTL: Set Logical Drive                   . DOS 3.2

    Sets the drive letter used most recently to refer to a device that has
    more than one drive letter.

       On entry:      AH         44h
                      AL         0Fh
                      BL         Drive number (0=default, 1=A, etc.)

       Returns:       AL         00h of only one letter is assigned to the
                                          block device
                                 Highest letter assigned to block device
                                          (1 = A, 2 = B, etc.)
                      AX         Error code if CF is set

  --------------------------------------------------------------------------

    Some block devices use more than one drive letter to refer to the same
    device.  For example, the floppy disk drive on a system with only one
    floppy disk drive can be referred to as either A: or B:.  This
    function sets the drive letter used most recently to refer to a drive.

       Notes:         Function 440Eh can be used to get the most recent
                      drive letter used to refer to a device.

                      If you issue an I/O operation using a drive letter
                      other than the most recently used drive letter, DOS
                      will issue a message "Insert diskette for...".  You
                      can avoid this message by changing the current drive
                      letter before issuing any I/O function calls.