What is OEM Windows? How It’s Different From Retail Version Of Windows?
[…]The OEM Windows has its product key tied to a particular device. While the retail product key also works on one machine, it can be transferred to another one. Earlier, in the case of laptops, the OEM product key was written on the bottom part of the device. Nowadays, it’s embedded directly into firmware (BIOS or UEFI) of a device and used by Windows when required.[…]
https://fossbytes.com/what-is-oem-windows-vs-retail-windows/
Firmware Security 