Function 3306h          Get MS-DOS Version                           DOS 5.0+

    Returns the MS-DOS version number (unmodified by SETVER), revision
    number, and version flags.

        Entry   AX = 3306h

        Return  BL = Major version number
                BH = Minor version number (e.g. 02h for version 6.2)
                DL = Bits 0-2 = revision number
                     other bits reserved (0)
                DH = DOS version flags:
                     bit 3:  1=DOS runs in ROM, 0=DOS runs in RAM
                     bit 4:  1=DOS is in high memory area (HMA)
                             0=DOS is in conventional memory
                     other bits reserved (0)

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    This function returns the actual DOS version number rather than the
    version number set by the SETVER command, if any, for the program.