When running with Windows 95, MS-DOS – based applications can check the operating system version by using Get MS-DOS Version Number (Interrupt 21h, Function 30h). For Windows 95, this function returns 7 as the major version number and 0 as the minor version number.
If you need to know that the system is running MS-DOS version 7.0, you must use Interrupt 2Fh Function 4A33h. This function returns zero in the AX register for MS-DOS version 7.0 or higher and returns a nonzero value in AX for any other versions of the disk operating system. In addition to the AX register, this function uses the DS, SI, DX, and BX registers.