Microsoft has announced that it will be possible to upgrade Windows 7, Windows 8 or Windows 8.1, to the new Windows 10 (to be released), and that the users who will make this upgrade, are going to be able to use Windows 10 for free, as long as they own a Windows 7/8/8.1 key.
But not only for a year, the user who will make the upgrade will be able to use the new operating system as long as he wants, unless the OS needs to be reinstalled because of any reason, like the hard drive will crash or your PC might get a nasty virus.
The only condition to make this upgrade is to do it in the first twelve months since the official release of Windows 10.
As it looks, Microsoft is trying to allow users to test Windows 10, like a demo, so they will decide if they want to stick with this operating system, or they just like the old versions more, Windows 7, 8 or 8.1.