Ah, the elusive method of booting on a PowerPC Mac: USB. For far too long it’s been said it’s not doable, or the results have been hit-or-miss, or the answer hasn’t been straightforward at all. Well today, there’s a surefire way to boot USB on PowerPC Macs – all thanks to DistroHopper39B from MacRumors. While there are a few guides and even YouTube videos on how to do this – when this precise question is answered on the internet, the answer isn’t always affirmative. This article covers every single “NewWorld” Mac from 1999 onward!

Digging into Open Firmware

After DristroHopper39B spent time digging into Open Firmware, he discovered a way to get OF to boot off of USB. This method doesn’t rely on having a USB drive that “happens to play well with OF” or any sort of external hub like other methods would. Instead, this method probes the USB ports after boot. All you need is a PowerPC Mac with a PowerPC OS (Can be Mac OS X, BSD, even linux!!) installed on it.

• Note: Only certain versions of Mac OS X are cable of booting cleanly from USB drives for some reason. Based on the MacRumors user’s testing, Leopard can boot reliably on every machine they tested, however, Tiger works on some machines while also not working on others. This is OS related.

The Process

You’re going to need a couple pieces of very important information in order to execute this task: USB Port ID, and the specific partition number. The partition number is rather easy to get, it’s available in: Disk Utility > USB partition > Info > Partition number. For most Mac OS X USB flash drives, the correct partition is usually 3.

Finding the Port ID is a bit more tricky, there are a few steps involved in this process. Credit for this process and information contained in this article all goes to DristroHopper39B.

• 1: Disconnect all USB devices from your Mac.
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• 2: Connect a USB keyboard to your Mac. If it has a hub, make sure nothing’s plugged into it.
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• 3: Boot to Open Firmware by holding Command-Option-O-F at startup.
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• 4: At the 0 > prompt, type:
  • dev usb0
    ls
    .
• 5: If there are any keyboard@X values, stop here. The number after usb is your port ID. If not, type dev usb1 and ls and keep incrementing that number until you find some. If you’re on a laptop, make sure there are no mouse@X values, since the internal keyboard and touchpad are sometimes connected via USB.
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• 6: Now, shut down your Mac by typing shut-down at the prompt. Unplug the USB keyboard and connect the USB drive you want to boot from to the same port you just had the keyboard connected to. If you’re on a desktop, reconnect the keyboard to a different port, and boot the computer back into Open Firmware.
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• 7: It’s now time to actually boot the Mac from USB. To do this, you need to issue this command:
  • probe-usb boot usb<port ID>/disk:<partition number>,\\:tbxi
    .
    
• 8: An example of this command with a port ID of 1 and a partition number of 3:
  • probe-usb boot usb1/disk:3,\\:tbxi

If all goes well, you should now be able to boot your OS of choice off of USB!

Online Resources

Link to original MacRumors Thead.