• Windows 7 uses a device identification string and device setup class to properly install a new device.
• Device identification strings: A device often reports multiple device identification strings. Hardware ID is the most specific device identification string. Multiple hardware IDs allow the best available driver to be installed. Compatible IDs are another device identification string that is used to find appropriate drivers.




Read more about device identification strings at:
http://msdn.microsoft.com/en-us/library/ff541224(VS.85).aspx.

• Device setup classes: Device setup classes are used during the installation process for a new device to describe how the installation should be performed. Device setup classes identify a generic type of device rather than a specific make or model. Each device setup class is identified by a globally unique identifier (GUID).
• Some devices have multiple GUIDs defined if they are a multifunction device such as a scanner/fax/printer device. The parent device (overall device) has one GUID, and other functions (scanner, fax, printer) each have their own GUID.

Read more about device setup classes at:
http://www.osronline.com/ddkx/install/setup-cls_1wpz.htm.