I’m a proud owner of both an Intel iMac and MacBook, while my girlfriend is still quite fond of her iBook G4 12″, and plans on keeping it for awhile. I previously owned a 14″ iBook, and when the Intel iMac arrived, one of the first questions I had was “Can I boot both PPC and Intel machines from a multiple-partition drive?”

I was wondering if I could still use the external drive which had multiple partitions and served as my backup drive. I use SuperDuper!, and would make regular backups to the drive from the 3 PPC machines we had.

When I sold my G4 Mac Mini in favor of an upgrade to an Intel-based iMac, it ushered not only my first desktop Mac into the house, but also a new puzzle: Intel Macs use the newer GUID partitioning format, which is built upon Intel’s EFI subsystem. PPC Macs use the older Apple Partition Map (APM) format.

A new persistent hiccup in my weekly backups followed. Uh-oh.

Originally intended to replace the aging and unloved Basic Input Output System (BIOS), EFI now heads up the boot procedure of the new Macs, taking over from Open Firmware in PowerPC-based Macs.

So wait- let me check… can I boot the Intel Mac from a PPC formatted backup?

I did some quick research, and the answer came back cloudy: No you can’t… well, sort of, yes. But really, no. Apple doesn’t want you to, it seems.

Huh?

I’m sure you’re a bit confused, as I was. But not to worry, because I’m about to walk you through the easiest, fastest, and surefire way to backup both a PPC Mac and an Intel Mac to a single drive with multiple partitions that will boot accordingly to both types- and the best part is that you’ll never have to wade through the terminal, or advanced features of Apple’s Disk Utility as others would have you believe.

Solutions for creating a Universal architectural deployment of Mac OS X won’t be available until 10.5 Leopard. When it arrives, users will be able to boot a external installation of Mac Os X on either architecture. Enterprise IT specialists have found a way using a variety of tools to create a Universal 10.4, but for the average user it’s not necessary to compile such a solution.

So let’s get started.

A One-Way Street

Since Intel Macs use the GUID partition format, and PPC Macs use the APM partition format, building your dual backup external drive is a one-way street: It must be partitioned using APM, and you’ll be using both the PPC and the Intel backups with the APM formatted drive.

I know what you’re thinking: “I thought Intel Macs couldn’t boot from APM drives…”

They can’t, if the installation of OS X on the APM partition is PowerPC-based. But they can, if it’s Intel.

The Mac OS X Installation Disc 10.4.6 included with new Intel iMacs, Mac Minis, MacBooks and MacBook Pros was actually formatted using APM. So despite the confusion about the two different architectures, the different partition formats, and the different boot firmware, there is enough in common among the PPC and Intel systems to make ourselves a nice bootable external drive that we can use to backup both our PowerPC and Intel-based Macintoshes.

First, using a PPC-based Mac we’ll partition our external drive using Disc Utility (Applications/Utilities/Disc Utility). Open Disk Utility, and plug in your external FireWire drive. Wait for it to appear in the left pane within Disk Utility. If this is the first time you’ve used the drive, it may need to be initialized.

When it appears, select the drive, and then select the partition tab within the Disk Utility. Select the volume scheme drop-down, and choose ‘2 partitions’.

Select the first partition, and call it whatever you like, same with the second.

In my example I’ll name one partition ‘PPC’, and the other ‘Intel’.

Select Mac OS X Extended (Journalled) as the format, and adjust the partition sizes accordingly using the slider.

When ready, select the partition button, and your external disk will be formatted.

Now, once the drive is formatted, close Disc utility, and close all your open programs, saving your work. Next, open SuperDuper! and backup your drive in it’s entirety to the partition called ‘PPC’ (or whatever you called it). When it’s complete, eject your external drive and plug it into your Intel-based Mac.

Open SuperDuper! on your Intel Mac, and do a full backup to the partition called ‘Intel’ (or whatever you called it).

That’s it, you’re done! You now have a drive that can boot the PPC partitioned backups for your PPC computers, and your Intel backups to your Intel-based Macs.

*Important notes: Firstly, you cannot boot the PPC partition on the Intel Mac, or vice versa. Secondly, make sure you’ve installed the most recent Universal version of SuperDuper! on both computers before attempting this.

This method has been personally tested and verified to work with SuperDuper!. I have not tested CarbonCopyCloner, as it is not yet a universal binary application.