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Function 440Fh          Set Logical Drive Map                        DOS 3.2+

    Sets the active drive number for a physical drive that has more
    than one logical drive number.

        Entry   AX = 440Fh
                BL = Drive number (0 = default, 1 = A, etc.)

        Return  AL = 0   Physical drive has only one drive number
                AL > 0   Active drive number for the corresponding
                         physical drive (1 = A, 2 = B, etc.)
                or
                AX = Error code, if CF is set
                     | 01h Invalid function
                     | 05h Access denied
                     | 0Fh Invalid drive

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    Programs that set the active drive prevent DOS from prompting the
    user with the message "Insert diskette for drive x: and press any
    key when ready."