What about 9? Windows 8 must have been so bad that they're just skipping ahead to 10.

The goal with Windows 10, Belfiore stressed, is to "find UI approaches that use the same mouse and keyboard experience evolving from Windows 7 so the touch users get something natural."

Belfiore, during his demo, offered insight into what went wrong with Windows 8. The goal of that OS was based on "the effect that two-in-one's can have for the productivity of Windows to help people get things done," Belfiore said. Two-in-one devices can shape-shift from laptop to tablet, and Microsoft has hoped that Windows can dominate that dual form factor in a way that competitor Apple cannot, with its separate iPad and laptop lines.

"Windows 8's focus on touch, the large start screen, the notion of apps running full-screen as they do on tablet devices...that was to salute the idea that this would be more productivity," Belfiore added. "But we didn't get it right. With Windows 10, we think we got it right."
Some cool new things added too.