Mac OS 8.6 for Unsupported Systems

Apple released the early G4s, Yikes and Sawtooth, with special, updated versions of Mac OS 8.6. I’m not sure if people are aware, but @LightBulbFun did some excellent work here to produce a modified version of the Mac OS ROM file, that goes in the System Folder, to enable this special version of 8.6 to be booted on unsupported machines including the Pismo, Gigabit Ethernet G4, some DA G4s, perhaps some extra iMacs that are not usually supported, some iBooks, probably the Cube and perhaps some early PowerBook G4s? The requirements are that the machine needs to have an old enough processor and be similar to an officially supported machine. Machines with the G4 7450 processor and newer are not immediately supported without some further fiddling in OpenFirmware.

Issue 1 – 20240221

Note – a bug in issue 1 prevented the Restore functionality from working.

I decided to take this modified ROM file and wrap it up in a modified version of the Mac OS 8.6 installer CD. I’m not going to lie, while most of it was easy, getting the Installer application on the CD to actually install the modified file was way more tricky than I expected. Yes I tried replacing the file in the two tomes it appeared in. That lost me about 5 hours of my day. Yes I tried editing the install scripts, it wasn’t possible to convert them between their compiled state and editible state easily, given my poor knowledge of the Apple Installer SDK. Right. Anyway.

Make sure your computer is running the most up to date firmware. I forgot to and it caused me issues on my GigE G4.

Features of my CD image :

This CD should boot most supported unsupported machines, by holding the ‘C’ key.
The firmware updates you might need are included on the CD.
An Apple made Machine ID spoofer Control Panel is included in utilities in case you need it.
The installer works and provides a system with the modified Mac OS ROM file.
The restore application works and restores an image including the modified Mac OS ROM file.

Unintentional features :

For some reason, sometimes Pismos (perhaps other similar machines) power off when they start loading the desktop from a CD. Installed systems work just fine, but you might need to boot from another disc while you install.

Things I did :

I modified the restore image to add the Mac OS ROM file.
I modified the CD System Folder to add the Mac OS ROM file.
I added the Machine ID control panel in Utilities (but not the System Folder, I probably should have).
I removed the machine specific white-list from the installer program so it will launch on absolutely any machine, regardless of whether it is appropriate or not.
I made a new installer script, and tagged it on the end of the 8.6 update in the Installer, so that it silently swaps in the modified Mac OS ROM file without bothering the user.
I added a load of firmware updaters in a folder.
I added some ReadMes for clarity.
I messed up the order of the icons on the CD by accidentally clicking “Clean Up” when I didn’t mean to.

I have tested on a Pismo and on a GigaE G4, but would appreciate feedback on what other machines this disc works with. This disc isn’t a magic bullet – this will not work on a G5, or a Plus, see the thread linked above for OpenFirmware hacks to get 8.6 running on a QuickSilver or MDD, but that won’t work right out the box, so really only play with this if you have a Pismo, early TiBook, G3 iBook, Graphite G4, G3 iMac or Cube.

Issue 2 – 20240222

Following on from the above, I decided to make a few small changes. In addition to the above, I…

Added an updated (from Mac OS 9.2.2) version of the ATI drivers to the Installer and Restore Image.
Ensured that a newer version of the FireWire and Iomega Zip extensions (again from Mac OS 9.2.2) are installed if the selected option includes them.
Ensured that the updated extensions which the original installer only installs for the “PowerPC G4” are always installed, for example on a Pismo.
Deleted the Power Mac G4 ReadMe from the Restore Image.
Added a date to the top level of the CD, to assist with comparing versions.
Fixed the restore image by running the “Scan Image for ASR” script on it.

https://elephantandchicken.co.uk/downloads/CDImages/Mac_OS_8.6_Unsupported_G3_G4-iss2.zip

My hosting service isn’t great sorry. People in the Americas might find the connection drops. All I can say is sorry, but if you keep trying it eventually should complete. The download is approximately 425MB compressed.

Consider the software to be experimental. It might not work, but if it does, that is excellent news.

Notes on Compatibility

LightBulbFun and others have noted some compatibility issues.

To boot from the CD, the Macintosh must have a G3, 7400 or 7410 processor. Some newer G4 based systems can be booted, but require the cpu-pvr property is overwritten to spoof a 7400 processor. See details below.
Best results are generally achieved with an ATI card with a full ROM including an NDVR for classic Mac OS. This potentially excludes Snow iBooks and iMacs from compatibility.
When spoofing cpu-pvr, this CD still will not work with FW800 G4 MDDs.
On some machines, only the ATA66 bus will be recognised.
Ensure your Macintosh’s firmware is up to date.
Sometimes on the Pismo it is not possible to fully boot from the CD and the computer powers down when it tries to load the desktop.

Running Mac OS 8.6 on Unsupported Processors

To boot a late model Digital Audio, QuickSilver, or FW400 MDD G4, power on your computer while holding Cmd+Opt+P+R on the keyboard. When you see a black on white command prompt, enter the following commands :

dev /cpus/PowerPC,G4
.properties
000c0207 encode-int " cpu-version" property
mac-boot

If you are intending to boot from the CD, substitute “boot cd:,\\:tbxi” instead of “mac-boot”.

Compatibility Matrix

The Unsupported Mac OS 8.6 disc image has been tested on the following machines, with results as shown.

Macintosh Model	CD Image Version	Installer Compatibility	Restore Compatibility	Comments
Power Macintosh G4 “Gigabit Ethernet” 500MP	Issue 2	Yes	Yes
PowerBook G3 “Pismo” 400MHz	Issue 2	Yes	Yes	Unexpected shutdown when booting from CD once
iBook G4 800MHz	Issue 2	No	No	Can’t boot, even with patches to model, compatible and cpu-pvr