Windows 10 is a free upgrade for all 7 and 8.1 users (update: RT too)
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.
Update: During a Q&A session after the event, Myerson promised that Windows RT users would get an upgrade to 10 as well. Your Surface 2 won't be left high and dry!
http://www.engadget.com/2015/01/21/w...-free-upgrade/
