Int 2F Fn 4680  U - MS Windows V3.0 - Installation Check                   [W]

   AX = 4680h

Return: AX = 0000h MS Windows 3.0 running in real (/R) or standard (/S) mode,
          or DOS 5 DOSSHELL active
      nonzero  no Windows, Windows prior to 3.0, or Windows3 in enhanced
           mode

Note:  Windows 3.1 finally provides an installation check which works in all
     modes (see AX=160Ah)

See Also: AX=1600h,AX=160Ah