Microsoft has begun saving the Windows 10 activation status for a device online. This means that once you’ve activated Windows 10 successfully, all future activations will be done automatically without the need for a product key.
The move makes clean installing Windows on a PC a much easier task, which previously required a product key for every installation. Microsoft ties every Windows activation to a specific device using a unique ID.
With Windows 7 and Windows 8, Microsoft used a hashed value that was recorded in its activation database alongside the product key. Later, reinstalling the same version of Windows on the same hardware with the same product key then automatically activated the software.
With Windows 10, the company stores a digital entitlement (Windows 10 license certificate) alongside the device ID if the install is detected as genuine. When a user reinstalls Windows 10, you don’t need to enter a product key to activate since the digital license is now tied to your hardware.
Long story short, once your Windows 10 install gets activated, you can now wipe your hard disk boot from Windows 10 installation media to have a squeaky clean PC. While the setup does ask you to enter the product key, it can be skipped.
If you reinstall with the same version of Windows 10 on the same hardware you should find yourself automatically activated. Just keep in mind that trying to install a copy of Windows that came preinstalled with a device you bought from an OEM on another PC will not work.
Still confused? Head here