How to activate Win10? How does Win10 judge the user equipment to meet the free upgrade conditions?

According to Microsoft's policy, all Windows Insiders test users and genuine Windows 7/8.1 users can upgrade freely after the official release of Windows 10. Prior to this, Microsoft has made it clear that as long as the user equipment has been installed with Win10, it will be unimpeded whenever it is installed again.

There is a problem. In the case of completely reinstalling the system, how does Windows 10 determine whether the user's device meets the "free upgrade" condition?

Gabriel Aul, the person in charge of Windows Insiders, explained that Windows 10 has an "Activation Service" that detects whether the user's original device contains genuine license information for Windows 7/8.1. Windows 10 is automatically installed and activated, and the entire process requires no user intervention and no need to re-enter the previous Windows 7/8.1 activation code.