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We do not know a lot yet about the operating system after Windows 8. Heck, we even do not know if it will be named Windows 9 or if Microsoft will give it a different name. Everything is possible at this point in time.
A leaked roadmap suggests that we might be able to play around with the next but one Windows earlier than everyone thought. The roadmap suggests that we may see a developer preview of Windows 9 at the Build 2013 conference which should takes place in the middle of the year.
The developer preview is then followed by the first Windows 9 Beta release during the January CES 2014 and a release candidate release during the MIX 2014 conference in April. The Windows 9 RTM would then be released during Build 2014 along with Internet Explorer 12.
The final version of Windows 9 will be released in November 2014 along with Windows 9 Mobile and Kinect HP2. Microsoft would release another operating system only two years after the release of Windows 8, which is expected to be released in 2012.