Install Mac OS X Leopard on a G4 800mhz Quicksilver

If you have an old G4 sitting around that’s at the 800mhz mark, you probably should try installing Leopard, because most people agree it actually runs FASTER than Mac OS X 10.4 Tiger. Weird, huh? I guess they’ve optimized the code pretty well.
However, when you try to install the operating system, you are warned that Leopard cannot be installed on your G4. There are a few reasons for this:
1) Leopard requires 512MB of RAM – you have RAM, right?
2) Leopard requires over 867mhz processor

We can fix number 1 by simply getting more RAM. I find Craigslist to be of great use here. Number two is a bit more difficult as G4 processor upgrades are ridiculously expensive once you consider the cost of a Mac Mini, and also requires a bit of tech savvy under the hood as you’d be swapping CPUs.
Not to worry, though. Here’s a way to convince OpenFirmware that your CPU is 867mhz, and allow the installer to boot, install, and get you off and running:
Boot into Open Firmware, I have covered this extensively here:
Once in OpenFirmware, issue the following commands (for single CPU):
dev /cpus/PowerPC,G4@0
d# 867000000 encode-int " clock-frequency" property
boot cd:,\\:tbxi

For dual CPU:
dev /cpus/PowerPC,G4@0
d# 867000000 encode-int " clock-frequency" property
dev /cpus/PowerPC,G4@1
d# 867000000 encode-int " clock-frequency" property
boot cd:,\\:tbxi

Note that all we are doing is over-writing the CPU clock-frequency (speed) property for each CPU installed, at boot time.
Also, if you need to boot another device, try:
printenv boot-device
This will return a list of boot devices to use when booting the installer. I used this in order to boot a Firewire device that had had a disc image (DMG) restored to it, making things a bit easy and faster.

Good luck!

10 thoughts on “Install Mac OS X Leopard on a G4 800mhz Quicksilver

  1. yes this worked first time for me after inserting disk and rebooting from hard drive when i reached the point where it told me it could not be installed on my machine

  2. Thanks! On my ancient G4 tower, this worked, but note that “clock-frequency” worked;
    ” clock-frequency” did not.

  3. this would be great for me, i “NEED” leopard, but i’m about 76mhz to slow..
    i just want to confirm that this will work fine with no problems..
    has anyone besides these two people done this?

  4. ok, can someone help me? I tried but got an error for the last, command. I got, “load-size is too small”. Am i doing this right? there are 3 seperate commands you have to type in? first being dev, second being d# and third being boot? Thats how i tried it and everything was fine for the first 2, got “ok”‘s. but for the last, it said the load size was too small? how do i get around that/fix it?

  5. Are you trying to install from DVDROM? Do you have multiple disc drives?
    TBXI needs to be on CD in or der to run “boot cd:,\\:tbxi”
    This means:
    1) boot
    2) boot tbxi
    3) find it on the root “\\” of the device “cd”

  6. I tried to boot this off of the dvd by using “boot dvd:,\\:tbxi” and I got the gray screen with a circle with a line through it (like in a no smoking and no parking sign)

    I restarted the computer and got the same OS X cannot be installed on this computer…


  7. Load Size too small– solved for me. I also received the “load size too small” error on submitting the final command line. My problem was that I had typed a space after the comma and before the \\. By removing the space everything went smoothly. Also in regards to another comment above about spacing– on my machine ” clock-frequency” (preceding space) worked but omitting the space didn’t work. (i-Mac- the one that looks like a desk lamp)


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