Microsoft announced it some time ago : the major updates of Windows will now be much more regular. We must therefore expect updates every year, as was the case for Windows 8.1. Presumably a version 8.2 of Windows will be released in 2014. But according to Mary Jo Foley of ZDNet, the operating system might receive a major update in 2015.
According to the journalist from ZDNet, the code name adopted by Microsoft to define this new edition of Windows would be "Threshold". The Redmond company currently be working on this version which concern the desktop OS, but also devices running Windows Phone and Xbox One. In fact, Windows, Windows Phone and Xbox One OS already share a common heart under Windows RT. With Windows Threshold, the goal would be to create a more unified OS between the three platforms. And deliver at the same time a Windows Store common to all devices. Threshold is for the moment a code name and we do not know if the final version will be called "Windows 9" or not. For information, Threshold means a planet around which the first halo ring orbited in the original Halo game launched back in 2001.
Mary Jo Foley finally states that an update of Windows 8.1 is under development. It would not be Windows 8.2, but Windows 8.1 Update 1 (you got lost?). This version will be released at the same time as Windows Phone 8.1, in the spring of 2014.
