Reinstalling Mac OS 9 on a PowerMac G4 MDD

The PowerMac G4 MDD 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.

PowerMacG4-MDDDue 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 PowerMac G5 for over a year. They never pushed this option on the Apple Store but it was a consistently strong seller.

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, rather 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. (Note: only MDDs without FireWire 800 ports can boot into OS 9, models with FireWire 800 ports require OS X. The install CD I used is Apple part number 691-4078-A.)

Recently I was contacted by a client who was looking for just this. He had a dual 1.25GHz MDD with some older ProTools hardware, and preferred to run the software in OS 9 rather than OS X. The problem was his installation of OS 9 was 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 5 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 are 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 here are our old friends Applications (Mac OS 9) and System Folder, just as we know and love.

To test this worked before sending to my client, I copied the two folders to an external FireWire drive (formatted with OS 9 drivers), then connected this to my MDD running Tiger. The Startup Disk Preference Pane showed the external drive with Mac OS 9 as a valid boot choice. Restart, a few screen flickers later, and voila! Welcome to Mac OS 9.2 appears on the screen.

Mission accomplished. I now had 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.

The story continues: Mac OS 9 Isn’t Dead Yet…

Update June 2012:
Mac OS 9 for PowerMac G4 MDD has been made available for download via the Macintosh Garden.

14 responses to “Reinstalling Mac OS 9 on a PowerMac G4 MDD”

  1. Adam Rosen says:


    Anonymous said…
    Adam, would you have the cd’s available to purchase?
    Paul, Cambridge MA
    March 31, 2011 at 9:25 AM

    Adam Rosen said…
    Paul, please contact me at
    March 31, 2011 at 9:17 PM

    Jochen said…
    Hi Adam,
    thank you very much for this detailed Information.
    I managed to get me a D691-4409-A Disc which is a Restore disc for the 1,25 MDD Dual CPU (german). Unfortunately your instructions doesn’t seem to work. I do exactly as you wrote, extracted the folders from OS9General.img onto a OS9 formatted HDD. When I boot with the option key pressed, I don’t get to boot from the local hdd.
    You have a hint for me?
    July 8, 2011 at 8:27 AM

    Adam Rosen said…
    Try booting from an external FireWire drive with Mac OS X installed. Make sure you can you can see the internal disk on the desktop. If so, try using the Startup Disk Preference Pane to select the OS 9 system as the startup drive.
    July 8, 2011 at 9:41 AM

    Anonymous said…
    Hello Adam, I have a problem with the “sibling links” on my dual boot machine. I need to look at some files in OS9 on the old machine but can’t open them as “the program that created it cannot be found”. I’ve tried to find the files that you mention above (on the original CDs) in order to reinstall OS9 system, but can’t open any of the files for the reason above. I’m feeling this might be terminal. Do you have any hints please? Thanks, Alex
    May 14, 2012 at 12:27 PM

    Adam Rosen said…
    Hi Alex, your situation is probably not terminal but you need more software than you currently have. I can help you get a copy of the Mac OS 9 software or convert your existing files to modern readable formats. If you’d like to arrange for these services contact me directly by email (
    May 14, 2012 at 9:47 PM

    Yves said…
    Hi Adam!
    First of all; thanks for this blog! You’re a life saver :-) I managed to boot the MDD with an OS9.2.2 disk hanging on firewire by using the above procedure. One small issue though: when the machine booted OS9 for the first time; i came into the welcome screen, filled in everything and then i come into the desktop but… It has only a trash icon and my HD with OS9 present?? No Apple menu, no special menu and thus no possibilty to shut down (unless pressing power button long enough) Have I missed something here? I used the original restore disk 1 or can this be a hardware issue like PRAM battery or something? Many thanks in advance and greetings from Belgium!
    October 18, 2012 at 5:50 AM

    Adam Rosen said…
    Try zapping the PRAM (CMD-OPT-P-R) at startup, then rebuild the desktop (hold down CMD-OPT during boot until prompted to rebuild). If neither works you might try reformatting and installing again.
    October 18, 2012 at 8:37 AM

    Yves said…
    Thanks for the fast reply Adam! PRAM-reset I already performed to no avail but rebuilding the desktop did the trick! Thanks again and have a nice weekend. OS9 rules! ;-)
    October 19, 2012 at 9:46 AM

    BluePowder said…
    Thanks very much for those informations.
    I managed to retrieve the specific 9.2.2 os, format one of my drive with the os9 drivers, copied the foldes onto the drive, and it boots onto os9.
    I have a g4mdd, however i can’t seem to write on the disk, i don’t have the privileges.
    I almost know nothing about os9, any help would be really great!!
    March 12, 2013 at 10:47 AM

  2. skinnie says:

    Hi, downloaded your cds on macintosh garden, to install on my Gigabit Ethernet, it now detects an os9 system but when I try to boot to it, a floppy with a question mark appears and my hdd starts spinning, any idea?

    • Adam Rosen says:

      Try restarting and hold down the Option key after the chime, then at the select disk menu see if you can choose the Mac OS 9 disk. Sometimes it also helps to zap the PRAM before rebooting into OS9: hold down CMD-OPT-P-R at startup until the system chimes and reboots again.

  3. NIcola says:

    I have my old G4 MDD dual 1.25 and I have OS9General.dmg
    i try to burn it with Disk Utility and Toast, but it is not a BOOTABLE CD.
    I can only copy all folder and document on my hard disk and it work.


    thx a lot

    • Adam Rosen says:

      Nicola – Apple never released a bootable OS9 install CD for the G4 MDD. The only way to get the software was on the Software Restore CDs bundled with the computer; these booted into OS X and allowed you to reinstall OS 9 on the hard drive (extracted from OS9General.dmg). If you’re looking to install OS 9 on multiple MDDs or need an emergency disk, you may want to make up a FireWire drive containing OS 9 then boot from the external disk.

  4. chrisNova777 says:

    does anyone have the powermac g4 original restore disk for the 1.25ghz MDD 2003?? the disc im looking for is a DVD, and its part number is z691-4409-a – it includes 10.2.6 mac os x + mac os 9.22 as well as AHT 2.02. someone i spoke to online has the disc but he claims hes never been able to successfully copy it. is this a known issue to anyone else?
    i have the 1.25ghz mdd 2003 model and would like to get its specific original disc to restore it to factory settings!

  5. Hi Adam, how did you create the partition on the external firewire hard drive and use the Mac OS 9 HDD driver to boot off it, Did you run the disktools in Classic to create the external partition, or is just “Blessing” the hard drive enough to set it as the active partition to boot from? I also used OS9helper in classic to update a OS 9.04 system that I copied off my previous Beige G3 Mac to install OS 9.2.2 within classic and make it bootable on a 2002 G4 Quicksilver that I built from pieces that I bought on Ebay.

    Thank you for the help, and the article!
    Jose F. Medeiros

    • Adam Rosen says:

      To format the FireWire drive you can either use Drive Setup in Mac OS 9 (Classic) or Disk Utility in Mac OS X; if using Disk Utility, make sure to select the option to Install Mac OS 9 Drivers. Once you copy over the System Folder you can use Startup Disk Control Panel (OS 9) or Preference Pane (OS X) to select the startup disk, or reboot and hold down the Option key to select a disk.

  6. Jeff says:

    I have a G4 mirror. It had 1 hard drive. Another computer I had was running system 9.2.2 for my Scitex, and it died. I took the hard drive and put it into the 2nd drive spot and hooked it up in the g4 mirror. I can see everything on that drive and I can access all the files. When I go into the system preferences and go to the startup disk and select system 9 and restart, I get a ? folder. When I try to reinstall system 9.2.2 I get a message Quicktime is not compatible, please upgrade to QT 6.0.3. When I try to start Classic it says the same thing. I need to run system 9 to run my Scitex software, any ideas?

    • Adam Rosen says:

      Hi Jeff, I would download the copy of Mac OS 9 needed for the MDD towers, and use that for either Classic or to startup in OS 9. The link is at the bottom of the post.

  7. Rhian says:


    I found a G4 powermac (the one with oval bay doors – quick silver model I think?) in the dumpster. Anyhow, I put a spare blank hard drive in it and it booted right up. It gives me the “wheres the os” ?/finder icon in the middle of the gray screen. Unfortunately I don’t have a FW drive or any clones of previous ppc 9 installs from back in the day.

    * I want to install OS9 classic on it but how does one open up the cd tray to put the cd in?
    * I do have some backups of my white intel iMac and my 08 intel MBP. If I switch them to a FW drive, will they work even though they are for intel machines?

    I’m hoping I just stick my OS9.2.1 disc into the g4 PM, and it should install 123 like my old bondi blue g3. Any other tips? Thanks for your help!

    • Adam Rosen says:

      Hi Rhian, if you continuously hold down the mouse button when booting up the Mac the CD drive door should open, shortly after the chime. Early QuickSilver models could boot Mac OS 9.2.1 but later ones could not. The Mac OS 9.2.2 version linked from this page will work, it requires a manual install as described. Systems for Intel Macs will not boot PowerPC models.

  8. Chy says:

    Hi Adam

    Thanks for your site – lovely. I had a collection of old Macs starting with a couple SE’s, moving up through 10 Classics, Colour Classics, several pizza boxes (LC, LCII, 430,etc),630, 4400, 6 Grey G3’s and 4 G4 towers as well as a couple of ancient laptops, an Atari STE and 2 BBC micros. Most of these I gave away to an IT technician friend who was starting a computer museum in his garage. I still have over a dozen original install/software discs for OS 9 and OSX for PPC, iMac, iBook, etc and wondered if they were worth keeping/passing on. They range from the old orange disks up to 2005 Mac Pro disks.

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