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Function 4400h (68-0)    IOCTL: Get Device Information

    Sets device information.

       On entry:      AH         44h
                      AL         00h
                      BX         Device or file handle

       Returns:       AX         Error code,if CF is set
                      DX         Device information

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    Subfunction 00h returns device information in DX. Bit 7 of DX is 1 if
    the channel is a character device, and 0 if the channel is a block
    device (disk file).

  DX for Character Device (Bit 7 = 1)

            Bit         Description
             0          Set if standard console input device
             1          Set if standard console output device
             2          Set if this is a null device
             3          Set if the device is a clock
             4          Reserved
             5          Set for binary mode, 0 for ASCII mode
             6          0 if end of file (EOF) on input
             7          Set to indicate a device (and not a file)
           8-13         Reserved
            14          Set if this device can process control strings via
                        subfunctions 02h, 03h, 04h, and 05h.
            15          Reserved

  DX for Disk File (Bit 7 = 0)

            Bit         Description
            0-5         Block device number (A = 0, B = 1, etc.)
             6          Set if the channel has been written
             7          0 to indicate a block device
           8-13         Reserved
            14          Set if this device can process control strings via
                        subfunctions 02h, 03h, 04h, and 05h.
            15          Reserved