System Locked Pre-installation

System Locked Preinstallation, often abbreviated as SLP, is a procedure used by major OEM computer manufacturers in order to preactivate Microsoft's operating systems Windows XP, Windows Server 2003 and Windows Vista before mass distribution. There are two different versions of SLP; 2.0 is used for Windows Vista and Server 2008 while SLP, which is now commonly referred to as SLP 1.0 to avoid confusion, for Windows XP and Server 2003. Operating systems that use SLP 1.0 check for a particular text string in a computer's BIOS upon booting. If the text string does not match the information stored in the particular installation's OEMBIOS files, the user is prompted to activate his or her copy as normal. SLP 2.0 works in a similar manner. This effectively "locks" the operating system to the qualified motherboard. In addition, if an end user feels the need to perform a "clean install" of Windows, and if the manufacturer supplies the user with an installation disc (not a "System Recovery" disc that is a hard drive image), the user will not be prompted to activate the copy, given that the installation is performed on the same motherboard. Furthermore, because the check only involves the BIOS and not hardware, a user is allowed to change virtually all hardware components within the machine, a procedure that would normally trigger re-activation in retail XP/Server 2003 copies.

It is important to note that SLP installations still require a product key, which are unique to the specific version of Windows (Home, Professional, Server, etc...). The product key printed on the Certificate of Authenticity affixed to an OEM assembled is sometimes said to suffice, but this is not necessarily the case. As of February 28, 2005[1], those keys were invalidated for normal activation by Microsoft in an effort to further reduce software piracy, but does not apply to SLP. If the COA product key is lost, then product key finders, readily available on the Internet, can decrypt the key from a local installation. Keys from either source will allow the user to avoid activation upon reinstallation. Also, Microsoft released the following generic product keys that can be used to avoid product activation on any SLP-enabled computer using the corresponding version of Windows XP:

(Please note that the following keys are not volume license keys. The installation source must also be SLP-enabled by the manufacturer. Microsoft has not publicly released an SLP key for Windows XP Home Edition, but the actual key from any SLP-activated installation of XP Home can be used on any other, regardless of brand.))

Windows XP Professional (32-bit)	MVF4D-W774K-MC4VM-QY6XY-R38TB
Windows XP Professional (64-bit)	FM634-HJ3QK-6QVTY-RJY4R-XCR9J
Windows XP Tablet PC Edition	XT67V-GY7FW-GR6FR-WDK2C-8T97J

Source: http://technet.microsoft.com/en-us/library/bb457078(TechNet.10).aspx