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This chapter describes the Open Firmware startup process by which Power Macintosh computers recognize and configure peripheral devices connected to the PCI expansion card bus. The Open Firmware process provides flexibility in system software to match the flexibility that the PCI bus provides for expansion hardware.
The PCI bus architecture described in the PCI standard supports the autoconfiguration concept of system configuration, because it includes mechanisms for configuring devices during system startup and defines expansion ROMs for plug-in expansion cards. The two code types currently defined for PCI expansion card ROMs are an Intel-compatible BIOS (Basic Input and Output System) code type and the Open Firmware type. Apple has chosen the Open Firmware type because it allows Power Macintosh computers to run nearly any operating system.
The iMac and computers introduced after the iMac implement the NewWorld system architecture. The NewWorld architecture relies explicitly on the Open Firmware startup boot process for devices attached to the PCI bus and other I/O buses. Peripheral devices that need to participate in the boot process at startup time in NewWorld computers must support Open Firmware as described in this chapter. An introduction to the details of the NewWorld architecture is provided in Introduction to the NewWorld Architecture.