Most of the Apple G4 models dropped support for natively booting Mac OS 9 and only support Mac OS X. Through a lot of hard work the folks at MacOS9Lives.com have been able to get Mac OS 9 booting on most of these systems. Below is a compiled list of tutorials from my own experiences, and the others from MacOS9Lives.

Unsupported Mac OS 9 Install Disc Image

There are a number of disc images available for multiple models at MacOS9Lives.com. I recommend burning these CDs with an application such as Toast Titanium.

Models known to work

  • Mac Mini - All models
  • PowerBook G4
    Best Models: [5,1], [5,2], [5,3], [5,4]
  • eMac G4 (1.25Ghz)
  • Power Macintosh G4 Mirror Drive Doors (1.25Ghz FW800)
  • iMac G4

Hardware Support

Most of these machines have newer hardware that was never available for Mac OS 9, therefore there are missing drivers and system components - not all devices will work. The most common issues are with unsupported sound cards, video cards, Bluetooth, and Airport cards. The most success has been achieved with machines that have an ATI Graphics card/chipset.

Preparation

Before you install Mac OS 9 on your machine, your Hard Drive must have the Mac OS9 disk drivers installed. You can do this with either of the following methods:

  • Boot from an OSX install CD, open ‘Disk Utility’ and partition/erase your HD with the ‘Mac OS Extended’ format. Ensure the option ‘Install Mac OS 9 Drivers is ticked!
  • Connect the Hard Drive into a computer already running Mac OS 9 and re-partition/format it with the application ‘Drive Setup’

Booting into Mac OS 9

This is achieved by performing some modifications in Open Firmware, and tricking your machine into thinking it has an different CPU version (This does not effect performance in OSX).

  1. Boot into Open Firmware by holding Command + Option + O + F when turning on or restarting your machine.
  2. Once Open Firmware has loaded you will need to open the NVRAM editor by typing nvedit, and then press Enter.
  3. Open the CPU device by typing the following:
    dev /cpus/PowerPC,G4@0 then press Enter
  4. Make the following modification to the cpu-version property:
    80010201 encode-int " cpu-version" property
  5. Enter device-end to close the CPU device.
  6. Press Control + C to close the NVRAM editor.

Performing the above will only offer a temporary method of booting into Mac OS 9. These commands need to be stored in the NVRAM so they persist between boots. Running the commands below will store this information in the NVRAM and restart the machine.

nvstore
setenv use-nvramrc? true
reset all

Your machine will restart and you should now be able to boot from the Mac OS 9 For Unsupported G4’s CD from MacOS9Lives.com.

Any data stored in the NVRAM will be erased if the machine loses power (e.g. is pulled out from the wall socket/power adapter, or has a flat battery. Since this is a lot to type each time this happens, a better way of performing the above is to write everything into a script, and tell Open Firmware to run it at boot. Now if you lose power you only need to remember one line to enter into Open Firmware.

Writing an Open Firmware Script

Open Firmware Scripts can be created with the application ‘SimpleText’, or a text editor that will allow you to save .txt files without any rich text (e.g. Sublime Text). Open SimpleText and add the following to your new document.

\ comment
cr
dev /cpus/PowerPC,G4@0
80010201 encode-int " cpu-version" property
device-end
boot hd:,\\:tbxi

The beginning of the script must contain an Open Firmware \ comment, followed by a carriage return cr.

The last line sets the boot device to the default HD so the machine continues to boot after running the script.

Save the file to the root of your hard drive and call it ‘bootscript’.

If you're worried about high hardware temperatures under Mac OS 9, see the post Controlling System Fans with Open Firmware. You can combine both scripts to make things easier.

Some PowerBooks have incompatible soundcards and will crash or refuse to boot OS9 after the above steps have been taken. If this happens try adding the following to your NVRAM, or script.

dev /pci@F2000000/mac-io/i2s/i2s-a
" screamer" encode-string " compatible" property
device-end

An example of this would look like the below:

\ comment
cr
dev /cpus/PowerPC,G4@0
80010201 encode-int " cpu-version" property
device-end
dev /pci@F2000000/mac-io/i2s/i2s-a
" screamer" encode-string " compatible" property
device-end
boot hd:,\\:tbxi

Installing from a CD

After booting successfully into Mac OS 9 you will need to install the system onto your hard drive. It’s a good idea to erase your HD with ‘Drive Setup’ if you don’t have anything important on it already.

If you install from one of the MacOS 9 Lives CD images start the restore process and follow the instructions. Once the restore process has completed DO NOT restart your machine. Open the ‘System Folder’, then ‘Extensions’ and remove the ‘Multi Processing’ folder. Move this to your desktop or delete it. This extension causes some incompatibilites and will freeze the system during boot.

If you install from any other CD/image the same step is reccommended.

Once the system is installed and you have removed the ‘Multi Processing’ folder, restart the machine. Once booted your machine may be stuck in a small screen resolution. If this happens open the ‘Monitors’ control panel and adjust the monitor arrangement.

If your machine has an ATI Graphics chipset it is highly reccommended that you add this driver modified by darthnVader from Mac OS 9 Lives. This adds better compatibility with more resolutions and color depths. Expand the file with Stuffit Expander and move the extension to your ‘Extenstions’ folder, which is located in the System Folder.