Microsoft had a reason for doing it, though the validity of that reason is... up for debate. They looked at the data for mobile devices (tablets mainly) and realized that people are using them to accomplish more of their traditional PC goals, like streaming video and music, browsing websites, and doing some light productivity stuff (email, notes). On the consumer software development side, developers and consumers seem to be more excited about mobile apps which are becoming more powerful and enabling people to do more. If you look at where Apple is going, their "post-PC" mobile devices are at the center of the operation. iMacs exist for people to store and stream local data and, crucially, develop apps for iOS (which can only be done on MacOS). Mac Pro's are for actual professionals who process the raw material that supports or becomes the content that eventually reaches us. Finally, there's the fact that Microsoft missed the boat altogether with the iPhone and modern smartphones, and they've had to spend a lot of time and money playing catch-up. This would not be an experience they want to repeat. So you take all of this into account and look at the problem of tablets. Microsoft *could* do exactly what they did with Windows Phone: develop a black hole for money that has to fight tooth-and-nail for a percentage of a percentage of marketshare (though it's more respectable now). Or they could get into this very important market by leveraging their most powerful piece of software: Windows. Microsoft couldn't compete with the iPad by developing a competing piece of ARM-based software (see: Windows RT), but if they could simply turn the tablet [i]into[/i] a PC, they could take it out of Apple's hands altogether. That notion probably gave Steve Ballmer a semi. Thus, Windows 8 (and RT) was born. It's an attempt to take over tablets by encasing them in a sexy coating of PC. Look at Microsoft's ultimate Windows 8 hardware, the Surface: at first glance, it's a tablet, but if you flip open the kickstand and flip down the keyboard (that's in every commercial!) it's a bona-fide miniature desktop. It has the full windowed environment, it has a USB port for your PC peripherals, it has a stylus to navigate the Desktop precisely... it's a PC. The problem that arises, which we are all familiar with, is what to do with actual desktop users. Laptop users can suck it up and get a new one with a touchscreen. Actual mouse-and-keyboard users can go cry in a corner.