This is the PCI device ID of the user's graphics card. Together with SystemInfo.graphicsDeviceVendorID,
this number uniquely identifies a particular graphics card model. The number is the same across operating
systems and driver versions.
Note that device IDs are only implemented on PC (Windows/Mac/Linux) platforms; on other platforms you'll have to do name-based detection if needed.
See pci-ids.ucw.cz for a list of device IDs.
See Also: SystemInfo.graphicsDeviceVendorID, SystemInfo.graphicsDeviceName.