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During system startup, the Open Firmware support code in the Macintosh ROM creates a device tree, as described in Startup and System Configuration When Mac OS is launched, it extracts device information from the device tree in the following steps:
Connections between name entries are formed when the entries are added to the Registry. The connections have direction and point from an existing entry to the new one.
The Expansion Bus Manager places most of the name entries in the Registry during system startup. However, some hardware provides standard ways to probe for devices and return information describing them. In this case, the low-level expert responsible for that variety of hardware finds the devices and adds their names to the Registry. The low-level expert attaches descriptive information for each device to the name entry as properties. Low-level experts are described in Terminology. In a few cases, drivers may enter names and properties in the Registry directly.
The software entity that creates a name entry owns it, whether it is the Expansion Bus Manager, a low-level expert, or a device driver. Only the owner should remove a name entry. Since most device drivers do not create entries in the Registry, most drivers never remove them.