Windows Product Activation

Windows Product Activation (WPA) is to ensure that Windows Vista is installed on only a limited number of computers .
Several Identifiers are used
Hardware ID : information generated from a computer hardware configuration
Product ID : A 25- character unique key supplied with the installation media
Installation ID : An identifier that Windows creates from the Hardware ID and Product ID.


During WPA Product ID and Hardware ID are sent to Microsoft. A single Product ID can't be tied to more than one Hardware ID. If the activation check finds that the Product ID has not been activated and tied to a Hardware ID, both ID are recorded and installation is activated. If the activation check finds the product ID is tied to a different hardware ID, the activation is failed.