Booting your Intel Mac to an APM-formatted drive

Here's a very handy article that explains how to boot an Intel-based Mac off an APM formatted drive.

Why would you want to do this?

Well, it's a very useful troubleshooting tool in Macintosh-land that you can boot a Mac off an external FireWire hard drive. This means that if the Mac you're looking at on your desk has a FireWire port, I can boot it off the copy of 10.4 on my external hard drive and run any and all necessary diagnostic and repair utilities to get it back up and running. I made good use of this recently when the HDD in my PowerBook crapped itself and I ran for a few days booting off a FireWire drive until the new hard drive arrived.

Anyway, back to the matter at hand.

Once the new-fangled Intel-based Macs arrived, along with their new firmware, the Extensible Firmware Interface (aka EFI) came a new disk partition format. Not a filesystem format, but a new method of laying out the partition table at the start of the disk.

Apple never updated the firmware in PowerPC-based Macs to recognise the new GUID Partition Table (GPT) for booting off the new partition format, and the OS X installer will not let you install OS X on an Intel-based Mac if it's using an Apple Partition Map (APM). You can't have two partition table types on the one disk, so this initially looks like a bit of a problem.

Enter M. Christopher Stevens, at Other World Computing who, with the assistance of a bit too much cough syrup, has found a way around it.

The short of it is that you get a FireWire hard drive and make two partitions. Then, install a system on a PPC machine, and then clone over an existing system from an Intel machine onto the second partition. Finally, bless the system on the Intel side, just to be sure and you should be right to go.

If you want to take it one step further, it may also be possible to create a single, universal partition that will boot either system, by following the steps in this Mac OS X Hints Article.

Let me know if you get it working =)