Even more confusing than a bunch of tiles: There are several versions of Windows 8. Most importantly, Windows RT, which comes built-in on the Surface RT tablet and other devices, is far less capable than Windows 8 and Windows 8 Pro. For more details on the difference, read our overview and Wired's review of the Surface RT tablet. In short, Microsoft will need to clearly explain that Windows RT is a mobile OS that shares the same skin as Windows 8, but is not a fully capable PC. It cannot run the same desktop programs as full Windows 8, only apps downloaded from the Windows Store.