Wondering how much Windows 10 will set you back? In most cases, nothing. Microsoft has announced that the new operating system will be a free upgrade in the first year for everyone using Windows 7, Windows 8.1 or Windows Phone 8.1. The company sees Windows as a service rather than a product, Terry Myerson explains. Yes, Microsoft is partly following in Apple's footsteps (OS X upgrades have been free since Mavericks), but it's hard to complain about getting a big update for free.