Genuine win7/8.1 User Reload Win10 how to activate?

Under Microsoft's policy, all Windows insiders test users and genuine Windows 7/8.1 users can be upgraded free of charge after the official version of Windows 10 is released. So the question is, in the case of a thorough reload of the system, how does Windows 10 determine if a user's device meets the "free upgrade" condition?

Windows 10 has an "activation service" that detects whether a user's original device contains the genuine licensing information for Windows 7/8.1 once the test passes, Windows insiders owner Gabriel Aul explains. 10 is automatically installed and activated, and the entire process requires no user intervention and no need to re-enter the Windows 7/8.1 Activation code.

In other words, genuine Win7 and Win8 users, the reload system does not need to worry about activation issues.