I get a lot of questions about Windows product keys, probably because some of my most popular content revolves around finding lost Windows product keys. You can't reinstall Windows without a valid, unique product key so it's no wonder that so many people put so much effort into finding their Windows key code.
I put together this FAQ to help answer some of the more common questions I receive about Windows product keys.
"I heard that a working Windows product key is included somewhere on the Windows CD/DVD. Is that true?"
No, it is not... with a small exception.
If you have a retail copy of Windows, be it Windows 7, Windows Vista, or Windows XP, there will be no product key stored anywhere on the CD/DVD.
If, however, you have a restore CD/DVD from your major computer manufacturer there might be a product key stored in a file on the disc but it will not work when reinstalling Windows.
This product key, if it exists, is the generic product key that Microsoft allowed your PC builder to use when mass producing computers. In other words, everyone's disc has the same product key. Your unique key for use when reinstalling Windows will be the one on the sticker on your computer.
Windows activation will fail if you use this product key to install Windows. If you've already made this mistake, just change the product key to the one on your product key sticker and then try activating Windows again.
"Can I use the same product key to install Windows on more than one computer?"
Yes and no. Technically, you can use the same product key to install Windows on as many PCs as you want but it's not legal and you won't be able to activate Windows on more than one computer at a time.
After a certain period of time, activating Windows is necessary to continue using the operating system, especially in more recent versions of Windows.
"Can I use the product key from one version of Windows to install a different version of Windows?"
No, you can not. Windows product keys are exclusively associated with a particular version of Windows.
For example, you can not install Windows 7 Home Premium with a Windows 7 Professional product key, nor can you install Windows Vista Business with a Windows 7 Ultimate product key. You can only use your product key for the specific Windows operating system version for which it is coded.
"Can I use someone else's Windows CD/DVD to install Windows on my PC as long as I use my original product key?"
Yes, you can. Windows product keys are not tied to specific CDs or DVDs, only to specific versions of Windows (see the question above).
In other words, you're welcome to use a friend's retail copy of Windows 7 Home Premium to reinstall Windows on your computer as long as you use your unique Windows 7 Home Premium product key.