With the advent of Windows 8.1, the very first rumors about the next major Windows wave emerged, and that time, Mary Jo Foley made reference to a major update planned for the spring of 2015.

Now, the ZDNet journalist got more information about the roadmap, finding that the project is code-named “Threshold’, the upcoming versions of Windows OS for PCs, smartphones and Xbox.

The sources — familiar with the company’s matters — confirmed that Terry Myerson, Vice President of Operating Systems, cited the codename “Threshold” in an email sent to employees.

If all goes as planned, Threshold will include updates for all platforms, namely Windows, Windows Phone and Xbox One, introducing many elements in common. And then, the update is referred to a single operating system, nor will be the likely merger between Windows Phone and Windows RT.

For a quick note, Xbox One OS, Windows 8.x and Windows Phone 8 share the Windows NT core. In addition to a single digital store for applications and the development of similar tools for the three platforms that allow you to achieve the common app, Microsoft has plans to add more functionality shared between the Windows operating systems, likely to arrive spring 2015.

Recently, Julie Larson-Green, Executive Vice President of Devices and Studios, said in an interview, “We aren’t going to have three different versions of Windows.” Earlier we also reported that Microsoft is merging its app hubs for Windows RT and Window Phone into a single digital app store, which is a sheer indication of unification of Windows ecosystem, following Apple footsteps.

Moreover, Windows 8.1 Update 1 is also expected, known as “spring 2014 GDR,” and Windows Phone 8.1 could debut early next year.