DOS Fn 3306H: Get DOS Version Info

                                                         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 Function Index - by DOS Version
          DOS Versions (overview and history)
          System Information Functions
          DOS Functions