We had an inkling that Microsoft would at least offer two versions of their next operating system (one for ARM devices and one for x86), Windows 8 when it finally launches in the middle of this year. The Redmond firm has officially announced three – Windows RT for ARM devices, Windows 8 and Windows 8 Pro. Like previous SKUs before it, Windows 8 is the basic package for the next-generation system, with add-ons provided for Windows 8 Pro users like Microsoft’s Media Center and the like. Windows RT meanwhile, will include touch-optimized desktop versions of the new Microsoft Word, Excel, PowerPoint, and OneNote.
Source: Microsoft