Booting Mac OS X

Booting Mac OS X:

"This page contains a brief description of the Mac's firmware (analogous to the PC BIOS in many respects), the bootloader, and the typical Mac OS X boot up sequence. There are significant differences between how older (68k, 'Old World' PowerMacs) and newer (everything currently, but essentially 'New World' machines with Open Firmware 3.x that load ROM from a file) boot. The discussion here applies to the newer systems."
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An Open Firmware implementation is based on the Forth programming language, i particular, the FCode dialect (FCode is an ANS Forth compliant dialect that support compilation of FCode source to bytecode). Apple and Sun are two prominent compute system makers that use implementations of Open Firmware in their systems (Sun' trademark is called OpenBoot). The Open Firmware Working Group's home page is hosted at various places, including Apple and Sun.
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Even though this Forth "shell" supports reasonable (for a BIOS) command line editin (you can use ctrl-a to go to the beginning of a line, ctrl-e to go to the end, ctrl-u to erase a line, the up-arrow key for history, etc.), you would find it more convenient (particularly if you are trying to write any code in the firmware) to access a Mac's Open Firmware from another (arbitrary) computer, over the network.