Windows Product Activation - technical definition

The method used to activate Windows XP for single-user licenses. Bulk licenses to companies do not contain Windows Product Activation (WPA). When XP is installed, WPA combines the XP product ID with identification data from the hardware components it finds in the machine (display, SCSI, IDE and network adapters, hard drive serial number, processor type and serial number, etc.). This combined ID (the HWID) must be transmitted to Microsoft within 30 days, whereby Microsoft returns an internal authorization that is stored in the operating system, making it valid. If more than six hardware components are replaced, the activation must be done again. See HWID.