Open Firmware

Open Firmware was a bootloader used on PowerPC Macintoshes. It is not actively used anymore.

Boot in OpenFirmware Prompt
Hold command-option-o-f during boot to get the Open Firmware prompt.

List Hardware
List hardware with memory addresses: dev / ls

List aliases of devices: devalias

For example, if this list may define a shortcut "hd" (hard disk) for the following hardware address: hd    /pci@f2000000/mac-io@17/ata-4@1f000/disk@0

List File System
dir hd:5,\

Lists the files of partition 5 of the "hd" device.

dir hd:\

Lists the files of the default partition of the "hd" device.

To eject a CD:

eject cd

Boot
Boot with the default settings (as stored in the boot-device NVRAM setting): mac-boot

Boot with the file yaboot, on partition 5 of the "hd" device: boot-device hd:5,yaboot

Boot with the file with TYPE code "tbxi" in the root folder of the default partition of the "hd" device (this is the default): boot-device hd:,\\:tbxi

NVRAM parameters
Display all NVRAM settings: printenv

Change an NVRAM setting: setenv boot-device mac-io/ata-4@1f000/@0:2,\System\Library\CoreServices\BootX

More information:
 * Fundamentals of Open Firmware, Part I: The User Interface
 * Booting Mac OS X. Excellent overview at kernelthread.com
 * Technical Note TN2001: Running files from a hard drive in Open Firmware. Slightly off-topic, but interesting nonetheless.
 * Open Firmware Quick Reference. Formal description of a few commands.