Function 30h (48)        Get DOS Version Number
 
    Returns the major and minor version numbers of DOS.
 
       On entry:      AH         30h
 
       Returns:       AL         Major version number
                      AH         Minor version number
 
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       Example:       If this call were used under DOS 2.11, AL would
                      return 02h, and AH would return 0Bh (11 decimal).
 
       Notes:         DOS 1.x returns 00h in AL.