Microsoft tried to make Windows’ activation process simpler with the release of Windows 10. For the first year after release, through July of 2016, Microsoft is giving away Windows 10 to any user with an activated copy of Windows 7 or Windows 8.1 (excluding Enterprise version of Windows). All you have to do is either download the Windows 10 ISO, or use the Get Windows 10 app which will show up automatically in your Windows 7 or Windows 8.1 system tray, and then install. Your hardware signature is then registered with Microsoft, and your Windows 10 upgrade is activated without the need for a new Windows 10 product key. Reinstalling Windows 10 at a later time from “bare metal” isn’t a problem, because Microsoft will recognize the hardware signature from your previously-activated Windows 10, and allow you activate again without providing a product key.
But what you those of us purists who prefer to start with a clean slate and install Windows 10 bare metal in the first place? Microsoft has listened, and with the first big update to Windows 10 dubbed “Threshold 2,” your existing Windows 7, Windows 8.0, or Windows 8.1 product key will allow you to activate Windows 10 the first time you install. The big update to Windows 10 is expected to launch sometime in November of 2015. Read more here.