The only way to know if you like Windows 10 or not, of course, is to upgrade your system and give it a try. (Some 14 million people did just that in the first 24 hours of availability, Microsoft reported.) However, if you want to go back to your old OS, it appears that you're on a timer: Microsoft confirmed to Tom's Hardware that users will have only one month to decide if they want to continue with Windows 10 or not.
A Month To Decide On Windows 10?
A moderator on Tom's Hardware (darkbreeze) first discovered this issue, and when we reached out to Microsoft for more information, the answers we received raised some troubling potential issues.
Our initial thought was that this "one month" business simply meant you couldn't revert directly back to an old OS from Windows 10, but what about rolling back by simply performing a clean installation of your old OS? When we asked about that specifically, Microsoft dodged the question.
At this point, then, we aren't certain if you can return to your old OS by using a clean install, because it is possible that Microsoft will invalidate old activation codes after that first month. This would seem in some way to align with Microsoft's upgrade deal, as you can only get your free Windows 10 by upgrading from your old OS; you can't use an old activation code...