What is a Product Key?

Product Keys, How They're Formatted, and Why You Might Need to Find Yours

Image of a Windows 8 Certificate of Authenticity
Windows 8 Certificate of Authenticity. © Microsoft

The product key is a usually unique, alphanumeric code of any length required by many software programs during installation.

Product keys are also sometimes called CD keys, key codes, product codes, or installation keys.

Most software, including some operating systems and programs from most popular software makers, require product keys. As a general rule these days, if you pay for a program, then it probably requires a product key during install.

Unique product keys help software manufacturers ensure that each copy of their software was legally purchased.

In addition to product keys, some software makers, including Microsoft, often require product activation to help further ensure that software is obtained legally.

Microsoft Product Keys

All Microsoft Windows operating system versions require the entry of unique product keys during the installation process, as do all versions of Microsoft Office and most other Microsoft retail programs.

Microsoft product keys are often located on a product key sticker, an example of which you can see on this page.

In most versions of Windows and other Microsoft software, product keys are 25-characters in length and contain both letters and numbers.

In all versions of Windows since Windows 98, including Windows 10Windows 8, Windows 7, Windows Vista, and Windows XP, product keys are of the 5x5 set (25-character) form as in xxxxx-xxxxx-xxxxx-xxxxx-xxxxx.

Older versions of Windows, like Windows NT and Windows 95, had 20-character product keys that took the form of xxxxx-xxx-xxxxxxx-xxxxx.

See my Windows Product Key FAQ for more information about Windows product keys.

Locating Product Keys

Since product keys are required during installation, finding that you've lost a product key could be a serious problem if you need to reinstall a program.

The unique product key entered for an operating system or a software program is typically stored in an encrypted format in the Windows Registry, at least in Windows. This makes finding one very difficult without some help.

Luckily, there are special programs called product key finders that will locate these keys, so long as the program or operating system hasn't already been erased.

See my Free Key Finder Programs list for updated reviews of the best of these tools.

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