Those of you who have paid Microsoft a license to have Windows legally know what a product key means.
If at some point you want to move Windows to a new computer and do not intend to use the old one, you do not have to pay for another operating system.
If your license is not OEM but Retail you can enable the old copy of Windows on your new computer.
The easiest way to turn on Windows 10 is to sign in to your Microsoft account. In case you did not know, the Windows license is linked to your company account. To validate the product key, the operating system sends some information to Microsoft servers. This data is unique to your computer (processor and motherboard information). So if you change hardware on your computer, ie a new CPU or motherboard, the Windows you are running will probably shut down.
So if you can't activate your operating system by logging in to your company account, you'll need to use the Windows 10 product key. Some computers (OEMs) probably have the key on a sticker. If it is indistinguishable there is ShowKeyPlus.
ShowKeyPlus is a free tool that finds your Windows product key. Run the program and it will show you the operating system name, product ID, version and key. It also shows you if your license is OEM.
Click save and ShowKeyPlus will save the license data in a text file. You may find this information useful in the future.