Old World ROM

Old World ROM computers are the Macintosh (Mac) models that use a Macintosh Toolbox read-only memory (ROM) chip, usually in a socket (but soldered to the motherboard in some models). All Macs prior to the iMac, the iBook, the Blue and White Power Mac G3 and the Bronze Keyboard PowerBook G3 use Old World ROM, while said models, as well as all subsequent models until the introduction of the Intel-based EFI Models, are New World ROM machines. In particular, the Beige Power Mac G3 and all other beige and platinum-colored Power Macs are Old World ROM machines. In common use, the "Old World" designation usually applies to the early generations of PCI-based "beige" Power Macs (and sometimes the very first NuBus-equipped models), but not the older Motorola 68000-based Macs; however, the Toolbox runs the same way on all three types of machines.

PCI Power Macs with an Old World ROM contain an Open Firmware implementation, and a copy of the Macintosh Toolbox as an Open Firmware device. These machines are set to boot from this device by default, thus starting the normal Macintosh startup procedure. This can be changed, just as on New World ROM Macs, but with limitations placed on what devices and formats can be used; on these machines, particularly the early machines like the Power Macintosh 9500, the Open Firmware implementation was just enough to enumerate PCI devices and load the Toolbox ROM, and these Open Firmware revisions have several bugs which must be worked around by boot loaders or nvramrc patches. The Open Firmware environment can be entered by holding the key combination ⌘ Cmd+⌥ Option+O+F while booting.

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