: For older laptops or desktop towers, the product key is often on a Certificate of Authenticity (COA) sticker attached to the chassis.

If you have already purchased Windows 8.1 or have a computer that came pre-installed with it, you may already have a key without needing to download a new one:

: Using unauthorized keys violates Microsoft’s licensing terms and may prevent you from receiving critical security updates. Official Ways to Get a Key

A product key for Windows 8.1 is a used to activate the operating system and verify that your copy is genuine. While many users search for "free download" keys, it is important to understand how activation works and the risks associated with unauthorized keys. How to Locate Your Windows 8.1 Product Key