I own two Macs, a 13″ 2GHz Core 2 Duo Macbook that’s my main machine and an old 500MHz G4 PowerMac with 512Mb of RAM that I rescued from a skip last year sometime. Obviously the Macbook would be fine but I wasn’t so sure about the G4 so when I finally went down to the Apple Store on Regent’s Street in London I asked one of the clerks in the store who assured me it would be fine (having asked how much RAM I have in it). So based on the clerk’s recommendation I bought a family pack (allows up to 5 machines) only to find out when I got home that Leopard has an artificial floor of 867MHz for the processor.  My emotions ran through a journey of being pissed at Apple to pissed at the clerk from the Apple Store to determined to make the damned thing work.

I did some checking on my own but couldn’t find the file responsible for the limits, thankfully I found a collection of sites with some helpful info:

Forums on Macrumours.com
Installing Leopard on an Unsupported G4
Installing Leopard to an external firewire drive

Unfortunately neither method exactly fit my situation so using info from there and some general knowledge I did the following…

1. Rip an Image of the Leopard Install Disk, make sure you pick Read/Write.
2. Mount the Image.
3. Make a folder on the Desktop called OSInstall.
4. Open Terminal (make sure you have full permissions, might be worth elevating to root temporarily).
5. Type: “cd Desktop”, then press enter.
6. Type: “cd OSInstall”, then press enter.
7. Type: “xar -x -v -f /Volumes/”Mac OS X Install DVD”/System/Installation/Packages/OSInstall.mpkg”, then press enter (this empties the contents of the package to the current folder).
8. Use TextEdit to open the “Distribution” file (don’t quit Terminal yet).
9. On line 15 change the “var minRm = 512;”  to whatever value of RAM you need (e.g. “var minRm = 256;”).
10. On line 39 change the beginning of “866000000″ to match your processor (e.g. ”400000000″ for 400MHz).
11. Save the file and quit TextEdit.
12. Back in Terminal type: “xar -c ./ -v -f /Volumes/”Mac OS X Install DVD”/System/Installation/Packages/OSInstall.mpkg” (this rebuilds the package including the file you just edited), you can quit Terminal now.
13. If you have dual-layer DVDs you can skip the next part and just burn a disk directly form that and skip the next steps, otherwise secure yourself an external firewire or USB drive.
14. Use Disk Utility to create a partition of 10GB on the external drive, make sure you use the Apple Partition Map if the disk is to be used with a PowerPC Mac.
15. Use Carbon Copy Cloner to restore your image to the 10GB partition (Disk Utility might work but for me it gave me loads of errors).
16. Boot from the drive (hold Option / Alt during boot to select the boot disk).
17. Install Leopard!

Well, the install launches and it’s taken ages so far and still says there’s 30 minutes to go but once it’s done and I’ve got some use out of the system I’ll let you know how it runs.