Windows Pro, Windows RT, Windows Phone — it's all very confusing, isn't it? Microsoft thinks so, too.

But pretty soon, you won't have to worry about what version of Windows your device is running, because they will all be the same.

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At least that's what CEO Satya Nadella said to analysts during the company's quarterly earnings call on Tuesday. All signs were already pointing in this direction — the different versions of Windows share the same code, and one executive publicly commented that there were too many OSes — but this is the first confirmation that Microsoft is working to truly unify its core software.

"We will streamline the next version of Windows from three operating systems into one single converged operating system for screens of all sizes," Nadella said.

Nadella added that the work will be done "in the year ahead," putting Windows' grand unification on schedule with the arrival of Windows 9, due in 2015 at the earliest. When that happens, it would mean phones, tablets, desktop machines and even the Xbox would all run the same operating system, and the lines between Windows Phone and full Windows will be permanently removed. Windows software would simply adapt to whatever device is running it, similar in concept to responsive design.

That's not to say there won't be different ways the software is packaged for different customers. Presumably, Microsoft would still sell basic and "Pro" versions of Windows, and still offer special tools and custom modifications for enterprise customers. But ultimately, the software will be the same and able to run the same apps — something Microsoft has already enabled to a certain extent through Universal Windows Apps, which allow developers to design an app once and know that the app will run across all devices.

How will OS unity work on Xbox? And does it mean Windows Phones will get a desktop? A single team within Microsoft is working to answer those questions and many more over the next year. Unifying the design and engineering teams is another consequence of this move, and it dovetails with Nadella's recent announcement of streamlining internal processes at Microsoft and changing the culture.

With the move, Microsoft would be the first major platform creator to unify operating systems across devices. Apple and Google both have separate OSes for mobile devices (smartphones/tablets) and mouse-and-keyboard machines.