Super late reply to your question, but when you add Windows and punch in the key it links to the motherboard of the PC (laptop or desktop, doesn’t matter). Once you sign in to your Microsoft account, the key and mobo serial gets stored there. If you bought a new PC and with it a new motherboard you can find your key in your account or use the one on the back of your old laptop and delink it from your old device so that you can reuse it on your new one. It moves with your account.