Mac OS X Leopard on a First Generation iMac G4

Officially, this is not supported. Mac OS X Leopard will only install on a PowerPC G4 system that is approximately 867 MHz or faster. However, I recently came into an iMac G4 that is 700 MHz, so it would seem I’m cut off. Right?

Nope!

I managed to install Leopard on my iMac G4 and it runs just as smoothly as the latest version of Tiger. How did I do it? I found a list of steps elsewhere on the internets that I’ve refined and will share here.

Step 1: Create a Leopard DVD Disk Image

I imaged my retail copy of Leopard using Apple’s own Disk Utility that comes with OS X. I had read to do this, and I did it, but I suspect you may get away with skipping this step. If you want to be safe, go ahead and create an image.

Step 2: Find a USB Stick

If you have a USB stick, great. My iMac G4 only has a CD-ROM drive, so I can’t use the Leopard DVD. In fact, like the previous step, you may be able to skip this if your computer has a DVD-ROM. However, these are the steps I took, and it’s pretty cool to boot off a USB, so you can still do this if only for the fun of it.

What you’ll want to do is format your USB stick and make sure you put an Apple Partition Map on it by going into the formatting options. Presumably this enables the USB stick to boot.

Step 3: The Terminal

After I formatted my USB stick, I was then instructed to enable owners on it. I’m not entirely sure this is necessary, but it’s painless to do. Better safe than sorry.

Open the Terminal and enter the following command: sudo vsdbutil -a /Volumes/device

You may be required to enter a root password.

Step 4: The Clone!

Again, if your computer has a DVD-ROM and you have a copy of Leopard, these steps up until now may not be neccesary. Otherwise, the next step here is to clone that image you made (or clone the DVD directly) onto the USB stick.

I was made aware of some software called Carbon Copy Cloner which is free to use. It’s also pretty straightforward to use. Just make sure you check the option to erase destination files on the USB stick before cloning.

Step 5: The Moment of Truth

Whatever your intended method has been so far, this is where it all comes together. Put your DVD in your DVD-ROM, or your USB stick in a port, and reboot your Mac. Keep the Control+Option+O+F keys all firmly pressed until you enter the Open Firmware screen.

The point here is to trick Leopard’s installer into thinking your computer is a 867 MHz or faster machine. Also, if booting from USB, it’s entirely possible that your Mac doesn’t natively boot from USB… but it is capable.

These are the commands I entered:

dev /cpus/PowerPC,G4@0
d# 867000000 encode-int ” clock-frequency” property
boot usb1/disk:3,\\:tbxi

If you’re going to attempt booting from a DVD, you won’t need to enter that third command. That just forces the Mac to boot from USB… you won’t want that. usb1 may not work for you, either. It depends on which USB port you’re booting from. It could be usb0, usb2, etc. Keep that in mind.

With any luck, the machine will boot the installer, and it will be none the wiser. The only problem you may encounter is the slow speed at which it installs. On my 700 MHz iMac G4, it took just under 4 hours. Worth it, though!