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Name entries can be associated with many different things, including real devices and virtual devices. A virtual device is represented by a name entry for which there is no hardware. Any piece of software can add a virtual device just by creating a new entry in the Devices section of the Name Registry. It can mimic hardware to any degree by its selection of properties and its location in the tree topology. For example, a virtual device might enter only a logical address, using an AAPL,address property, or it might enter a full set of properties to mimic the behavior of a real device such as a SCSI controller.
Future versions of Mac OS will use the Name Registry to store information about many kinds of system components besides devices.