How to Run Leopard OS X on G4 PowerPC Macs

The G4 was Apple’s first serious pro computer after Steve Jobs became iCEO. Classified as munitions and under export restrictions because of its power, the G4 offered twice the performance of the G3 and three times the power of a Pentium 3 at the same clock speed.  When it came out in 1999, the government considered it by definition, a supercomputer.  Tiger (10.4.X), is the latest supported Mac OS for all G4s. Unfortunately, there’s not too much you can do with 10.4.  But, here’s an easy way to get G4s to run Leopard.  

First, make sure your firmware is up to date.  The latest firmware update is 4.2.8 for PPC G4s.  If you don’t have 4.2.8 installed, you need to install Mac OS 9 (9.1 to 9.2.2 will work) on a writable partition and boot to it.  Download the firmware, run the application and follow the onscreen instructions to reboot in service mode.

Second, 512 MB Ram is the minimum requirement for Leopard. Using less would be a painfully noticeable difference, so make sure you at least meet the minimum.  

Third, insert your Leopard OS X Install disc and shut down the machine.

Fourth, turn on your machine and immediately hold CMD + OPTION + O + F   until you get a black screen with white text.  This is open firmware, similar to bios in PC computers.  Leopard checks system information and if your processor is clocked under 867MHz, you WILL get a kernel panic error, which might be the scariest looking thing in the world.  Type these simple lines in Open Firmware and you can trick leopard in thinking you meet the processor requirements.

Single CPU G4s, use:

  • dev /cpus/PowerPC,G4@0
  • d# 8967000000 encode-int “ clock-frequency” property
  • boot cd;,\\:tbxi

Dual CPU Gr4s, use:

  • dev /cpus/ PowerPC,G4@0
  • d# 8967000000 encode-int “ clock-frequency” property
  • dev /cpus/ PowerPC,G4@1
  • d# 8967000000 encode-int “ clock-frequency” property
  • boot cd;,\\:tbxi

**Pay special attention to spacing.

**Hit “enter” and Open Firmware will display “ok” after each accepted line.