When Microsoft announced in 2011 it would create a version of Windows for devices running ARM processors, it seemed like a good idea. But Windows RT turned out to be a mess. Its most egregious sin is that it includes a semblance of the traditional desktop OS, but you can't install any desktop apps on it. The desktop portion just sits there -- a barren tundra on which a few lonely Office apps and built-in system functions go about their business. Windows RT's fail overshadows a secondary one: Microsoft didn't properly explain the differences between Windows RT and Windows 8 to the world. This is not how you launch a successful tablet OS in the age of turn-key iPads and Kindles.