Definition: Windows Product Activation
The method used to activate Windows for single-user licenses starting with Windows XP and Windows Server 2003. Bulk licenses to companies do not contain Windows Product Activation (WPA).
When Windows is installed, WPA combines the product ID with the identification data and serial numbers of the components in the machine (processor, drives, network adapter, etc.). This unique number, called the "Hardware ID" (HWID), must be transmitted to Microsoft within 30 days, whereby Microsoft returns an authorization code that is stored in the operating system. If more than six hardware components are replaced, the activation must be done again.