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 setup.
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.
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 10, Windows 8,Windows 7, Windows Vista, and Windows XP, product keys are of the 5×5 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.
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.