Typically each system has a unique 25 digit product key on its COA which is that systems license or right to run that particular version of Windows. This Product Key is usually present as a backup for Microsoft Product Activation in some rare cases and in general System Locked Preinstallation is used.
You may have noticed that the product key you obtained from your Alienware System after Clean Installation with a Windows 7 Reinstallation DVD or at Factory Settings is not the same as the unique 25 digit product key affixed to your system via its Code of Authenticity. This is because for Windows 7 OEMs such as Alienware use system locked preinstallation (SLP) keys.
The installation media inputs these keys and automatically activates Windows 7 if and only if a valid system BIOS is detected. In the case of the keys listed, a valid Alienware BIOS is required with the correct attached COA.
The reason for SLP Activation was to prevent the need for Alienware and every Alienware user from calling Microsoft to Activate or Reactivate their Windows Product.