Windows operating system including Windows XP, Windows Vista, Windows 7, Windows Server 2003, Windows Server 2008 and their R2 variants have 3 major distribution channels, namely retail (RTL), OEM (original equipment manufacturer), and volume licensing (VOL).

Within OEM distribution channel, which most end-users receive the license and product key for Windows when buying new PCs, things are not as straight forward as it seems. There are various different types of OEM license available. Although any OEM license with its product key will activate Windows operating system with the same features set for the installed edition, different OEM license types allow different way of activation methods.

Generally, OEM editions, which are distributed and supported by an OEM but not Microsoft, can be divided into following three kinds of product keys according to the license type:

  1. OEM:SLP (System Locked Pre-installation): OEM SLP keys are preinstalled by the OEM on the machine. End-users normally does not get to see the product key, unless when using product key viewers to retrieve the key manually. Data embedded in the BIOS (in SLIC table), together with the digitally signed certificate (OEM cert), is used to validate the product key. SLP keys will work with any OEM SLP system, regardless of the OEM system’s brand, i.e. not brand specific.

    OEM SLP product keys are the only keys that are able to perform offline activation instantly and locally, without going online or connecting to Microsoft server. OEM SLP keys are only issued to big manufacturers such as Dell, Asus, Sony, etc.

  2. OEM:NONSLP (Non System Locked Pre-installation): Similar to retail product key, but distributed and supported by an OEM. Non-SLP product key is also not brand specific. End-users are required to perform activation by phone or activate online.
  3. OEM:COA (Certificate of Authentication): The OEM:COA is normally provided via a COA sticker pasted on the casing (side or bottom body) of new desktop, notebook, laptop, netbook or nettop PC, which has already been activated with a pre-installed OEM:SLP key by OEM.

    Contrary to popular belief, the product key printed on the COA sticker is not used to activate the Windows, it’s master SLP royalty key that does the job. COA product key is provided as it would be required if a reinstallation of Windows is needed, unless users backup OEM activation beforehand. End-users are required to perform activation by phone or activate online.

Each product key for all editions of Windows in a distribution channel from Microsoft is associated with a same Group ID or Crypto ID. For Windows Vista, all retail and volume licensing product keys (RTL and VLK) belongs to Group ID 142, while OEM:COA is group 144, and OEM:SLP and OEM:Non-SLP belongs to group 146. In Windows 7, OEM:COA product keys belong to group 178, while OEM:SLP and OEM:Non-SLP belong to group 182.

After knowing different kind of product keys for OEM license available, how to check, identify and verify which license type a product key is belong to? Microsoft includes pidgenx.dll which used by WPA (Windows Product Activation) service to generate PID and determine the validity of a product key.

Basing on pidgenx.dll, a few programmers have written product key checker program for Windows. Download Product Key PIDX Checker for Windows 7.

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