Alternatively referred to as an activation code, Product Key, product id, registration key, and serial key, a CD-KEY is a group of numbers or letters that helps prevent software piracy. Software that requires a CD-KEY cannot be installed on a computer until a valid number is entered.
Above is an example of the Microsoft Windows XP Home Edition Product Key that can be found on the side or bottom of an OEM computer. In this example, the last four sets of letters and numbers have been hidden to protect the unique key. After Windows has been installed on a computer, it will prompt you for an activation key to verify your computer has a legitimate copy of Windows. Below, are the formats of the Microsoft Windows Product keys.
Windows 7, Server 2008, Vista, Server 2003, XP, 2000, ME, and 98
Product Key: xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
Windows 95 and NT
Product Key: xxxxx-xxx-xxxxxxx-xxxxx
Where do I find the CD-Key, Product Key, or unique number?
As mentioned above if you have an OEM PC (e.g. Dell or Hewlett-Packard) the Windows Product Key is found on the side or bottom of the computer. If you are looking for the CD-Key or another unique number to install a software program or game, that number is found on the CD sleeve, CD Jewel case, or the documentation included with the CD.
Windows 10 upgrade users
If you have installed the free Windows 10 upgrade the unique key is associated with your Microsoft account and can be re-activated after re-installing Windows 10.