Compatibility: 5.0+
Expects: AX    3306H
                                                                  
Returns: BL    major version number
BH    minor version number (note: binary value -- x.20 is 14H)
DL    revision number in low two bits (i.e., 00H to 03H)
DH    version flags:  bit 3 (08H)  DOS runs in ROM
bit 4 (10H)  DOS is in the HMA
                                                                  
Info: Returns information about the active version of DOS.  The return
value is not modified by Setver.

See Also: Fn 30H (get DOS version)
DOS Versions (overview and history)
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DOS Fn 3306H: Get DOS Version Info