Open Firmware USB Booting for PowerPC Macs

This guide explains how to boot a PowerPC Mac from a USB installer using Open Firmware.

Setup

Prerequisites

A USB installer drive created with macUSB is required to ensure reliable booting on PowerPC Macs.

Single-DVD and Multi-DVD editions are supported.

Boot Entry

Enter Open Firmware

  1. Insert the USB drive into your Mac.
  2. Power on the Mac and immediately press and hold: Command (⌘) + Option (⌥) + O + F.
  3. Release the keys when you see the white screen with the Open Firmware prompt.
Device Discovery

Identify the USB Disk Node

Find the Open Firmware USB alias that maps to your installer drive.

  1. Type dev usb0 and press Enter.
  2. Type ls and press Enter to list connected devices.
  3. Look for a disk entry in the output (typically disk@1, disk@2, etc.).
    • Note: If no disk entry appears, check other ports by typing dev usb1, dev usb2, etc., followed by ls, until you locate the disk.
Path Resolution

Resolve the Hardware Path

  1. Select the disk using the identifier found in the previous step (e.g., dev disk@1) and press Enter.
  2. Type pwd and press Enter.
  3. The screen will display the full hardware path (e.g., /ht@0,f2000000/pci@2/usb@b/disk@1). Note this path exactly as it appears.
Boot Invocation

Execute the Boot Command

Build the boot command from the hardware path obtained in Step 2 and the loader path. In most cases, the OS X loader (BootX) is located on partition 3. 

boot [your_hardware_path]:3,\System\Library\CoreServices\BootX

Example:

boot /ht@0,f2000000/pci@2/usb@b/disk@1:3,\System\Library\CoreServices\BootX
HARDWARE LIMITATIONS

Compatibility

USB booting capability is strictly dependent on the Open Firmware version and specific hardware architecture. This procedure may not be supported on all systems, particularly legacy PowerPC models.

Field Test Results:

  • iMac G5: Successfully tested; system boots correctly.
  • iBook G4: Open Firmware identifies the USB media, but is unable to initiate the installer.