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Startup Sequence

This section defines the startup sequence for Power Macintosh computers built prior to the iMac. The iMac and all Macintosh computers built after the introduction of the iMac are designed to support the NewWorld architecture. The startup sequence for NewWorld based computer models differs from that of previous Macintosh computers. And, it does so at no loss of software compatibility with well behaved applications. See Startup Sequence in the NewWorld Architecture for a high-level description of the NewWorld startup sequence.

Although the startup sequence for PCI-based Power Macintosh computers is different for each model, a typical sequence for a Power Macintosh computer running Mac OS can be summarized as follows, starting with the power coming on:

1. System-specific firmware performs initialization and self-testing on memory and other hardware systems.
2. The startup firmware in the Power Macintosh ROM probes each PCI bus, generates a device tree node for each device, and when it finds a device executes the FCode (if any) found in each PCI card's expansion ROM.
3. The startup firmware in the Power Macintosh ROM finds an operating system in ROM or on a mass storage device; it loads it into RAM and transfers processor control to it.
4. Mac OS completes the startup sequence.

The rest of this section describes these steps in more detail.

Initializing the Hardware

Running Open Firmware

Starting the Operating System