System Locked Pre-installation, often abbreviated as SLP, is a procedure used by major OEM computer-manufacturers in order to pre-activateMicrosoft Windows before mass distribution. SLP comes in five different versions:
SLP (commonly referred to as SLP 1.0)
These versions roughly coincide with versions of Windows NT (see table below). 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 OEM BIOS files, the system prompts the user to activate his or her copy as normal. SLP 2.0 and SLP 2.1 work 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 except motherboard, a procedure that would normally trigger re-activation in retail copies of Windows.
SLP installations still require a product key, which is unique to the specific edition of Windows, such as Home (XP), Starter, Home Basic, Home Premium, Professional, Ultimate, 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. On February 28, 2005, Microsoft attempted to reduce software piracy by invalidating those keys for normal activation, but this 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 (see below) will allow the user to avoid activation upon re-installation. However, since SLP 2.0 was introduced, hackers have been able to create modified bootloaders based on the Linux bootloader grldr; these are capable of emulating a SLP text string (such as one for Dell, Acer, and so on), so it appears to be present in the BIOS. This combined with an OEM certificate and OEM product key can instantly activate a Windows Vista/7 installation illegally but also be very hard to notice. This method can also be integrated into a Windows installation disk to activate on initial boot. Another method consists of modding the BIOS to insert the SLP 2.1 table, which can be used to replace blacklisted keys, or to add the SLP table to motherboards that do not have it (such as Gigabyte). Some brand-name computers such as Dell, already have the SLP table in their BIOS, which means that using software readily available on the Internet, a pirated retail installation can be converted to OEM, and the appropriate certificate installed into the OS, which results in Windows becoming genuine. Pirates refer to copies of Windows activated in this way as Pirated Genuine Microsoft Software.
Microsoft released the following generic product keys that users can enter to avoid product activation on any SLP-enabled computer using the corresponding version of Windows XP: (Please note that the following keys are notvolume license keys (VLK). 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. SLP-enabled installation CDs usually supply the needed key automatically, without the user having to enter one.)