11 types Windows CE, Windows 3.x, Windows 95, Windows 98, Windows 98 SE, Windows ME ,Windows NT, Windows 2000, Windows XP, Windows Vista and Windows 7. Hope I helped
If you are referring to Microsoft Windows, do you want to know about currently supported versions or how many through its history? If you mean how many different operating systems use a windowed graphical interface, that may be impossible to answer accurately. I believe there are 7 currently supported versions of MS-Windows: Windows 2000, Windows XP, Windows Server 2003, Windows XP Professional x64 Edition, Windows Vista, Windows Home Server and Windows Server 2008. If you consider XP Home Edition, XP Professional, XP Media Center Edition, etc. To be different versions, the count goes up (ditto for Vista Home Basic / Home Premium / Business / Ultimate / etc., and moreso if you consider the 64-bit versions too). Also, Windows 7 is available as a release candidate, though the official release is not scheduled until later this year. If you want to go back to the 1985 release of Windows 1.01, there have been about 25 versions (again not counting Home / Pro / etc. Or Service Packs as separate versions). If you're interested in a count of all windowing operating systems ... I wish you luck. Just counting Linux distributions with windowing interfaces is a daunting task, and then there are Apple OSes, DEC OpenVMS versions, ... 8-}
