Microsoft currently has three different versions of Windows running on mobile devices. But Microsoft is working to reduce that number, Julie Larson-Green, Executive Vice President of Devices and Studios, confirmed in an interview last week.
At present, Microsoft offer plain-old Windows for Intel-based PCs and tablets. There's Windows RT for ARM-based PCs and tablets. And there's the Windows Phone OS for Windows Phones.
I reported earlier this year that one of my sources said Microsoft is planning to whittle this down to two versions, though possibly not until the spring of 2015.
Read more at: Microsoft: We aren't going to have three different versions of Windows | ZDNet