Some devices are self-identifying--the device itself provides information to the system so that it can identify the device driver that needs to be used. The device usually provides additional information to the system in the form of name-value (name=value) pairs that can be retrieved using the property interfaces. See "Properties" for more information on properties.
SBus and PCI local bus devices are examples of self-identifying devices. On SBus, the information is usually derived from a small Forth program stored in the FCode PROM on the device. PCI devices provide a configuration space containing device configuration information. See sbus(4) and pci(4) for more information.