Adam's Apple

Installing Mac OS 9 on the Mirrored Drive Doors Power Mac G4

Adam Rosen - 2011.03.21 (updated) - Tip Jar

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The Power Mac G4 MDD (Mirrored Drive Doors) was Apple's last Mac capable of dual-booting into both Mac OS 9 and OS X. The last of the G4 towers, this model was originally introduced in 2002, briefly evolved into an OS X-only configuration with FireWire 800 in 2003, then returned to the original design for another year.

Power Mac G4 MDD Due to the need for some customers to run Mac OS 9 for several years after the introduction of OS X, Apple continued to sell this configuration online in parallel with the Power Mac G5 for over a year. Apple never pushed this option at the Apple Store, but it was a consistently strong seller.

Note that the only MDD models that can boot OS 9 are ones without FireWire 800. Models with FireWire 800 must use OS X.

These machines came set from the factory to boot into Mac OS X - with OS 9 also loaded on the hard drive. No OS 9 installer was provided; that was available as part of the Software Restore CDs bundled with the Mac. The MDD uses a model-specific version of Mac OS 9.2.2, newer than what was included on the last retail OS 9 installer. You need the bundled discs if you want to reinstall a bootable OS 9 on this machine.

Recently I was contacted by a client who was looking for just this. He had a dual 1.25 GHz MDD with some older ProTools hardware and preferred to run the software in OS 9 rather than OS X. The problem was that his installation of OS 9 had become unstable, so he was looking for the original installer. Did I have a copy of this rare item?

Off-the-shelf I did not, but fortunately I knew what he meant and where to get one. My last job before running Oakbog full time was as IT Manager for a recording studio, and we ran ProTools hardware and software on these very Mac models. We had about five of those systems at one point, so I suspected there were plenty of CDs still buried deep in drawers. Fortunately there were. I contacted my colleagues at the studio and arranged to get a set of the install discs.

My client didn't need Mac OS X, nor was he interested in first installing OS X 10.2.1 on his tower before restoring the OS 9 image. He just needed a bootable OS 9 System Folder. I suspected this was included on the set of four CDs somewhere, but it isn't a Finder-visible file.

A bit of sleuthing in Terminal helped find the mystery location. The OS 9 software is in a hidden directory called .images on the first disc.* Inside there several files including OS9General.dmg - I was able to mount (open) this disk image to the desktop via the following Terminal command:

%> open /Volumes/Restore\ CD/.images/OS9General.dmg

That takes a few minutes, then mounts a volume called OS 9 Content onto the desktop. Inside it are our old friends Applications (Mac OS 9) and System Folder, just as we know and love.

To test that this worked before sending it to my client, I copied the two folders to an external FireWire drive (formatted with OS 9 drivers), then connected the drive to my MDD running Mac OS X 10.4 Tiger. The Startup Disk Preference Pane showed the external drive with Mac OS 9 as a valid boot choice. I restarted - a few screen flickers later, and voilà! Welcome to Mac OS 9.2.2 appeared on the screen.

Mission accomplished. I now have a valid boot system for Mac OS 9 on an MDD, along with the disc image. My client was thrilled to hear the good news, and I sent him a copy on CD the next day.

Note: My install CD is Apple part number 691-4078-A (Power Mac G4 Software Restore, disc 1 of 4). Only MDDs with FireWire 400 ports can boot into OS 9; models with FireWire 800 ports require Mac OS X.

This article was originally published on Adam's Oakbog website. It has been adapted and reprinted here with his permission.

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Adam operates Oakbog Professional Services and The Vintage Mac Museum. He publishes The Vintage Mac Museum Blog. If you find Adam's articles helpful, please consider making a donation to his tip jar.

Recent Adam's Apple Columns

Mac OS 9 Isn't Dead Yet, 2011.05.16. In some areas, the need to run Classic Mac software or the cost of upgrading apps to OS X keeps people using Mac OS 9.
Vintage Mac Workhorse: Power Mac G4 Cube with Mac OS X 10.4.11, 2011.03.03. The G4 Cube has plenty of power and runs OS X 10.4 Tiger very comfortably, letting it act as a server accessible by new Macs and old.
Vintage Mac Workhorse: WallStreet PowerBook G3 with Mac OS 9.2.2, 2011.02.23. G3 Macs are ideal for the Classic Mac OS, and SCSI, ADB, and serial ports make the WallStreet PowerBook a great bridge computer.
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