Booting your Intel Mac to an APM-formatted drive
by M. Christopher Stevens

When the new Intel Macs were released, those of us who keep all our tools on a separate hard drive, found a nasty surprise - you can't boot an Intel-based Mac from an OS disk for a PowerPC Mac. That shouldn't be a problem, though. Just pop in the install disk for the Intel Mac, select your external hard drive and...

"You cannot install Mac OS X on this volume. Mac OS X cannot start up from this volume."

Well, that's not good...

Alphabet Soup

In the past, we could take a nice FireWire hard drive formatted on one machine, loaded up with an OS and some requisite tools, and use it to boot and troubleshoot another machine. All was warm and fuzzy in the world, until the new Intel-based Macs came by. All of a sudden, our trusty Emergency Drives were unable to boot.

What the heck is going on? It turns out that, along with the processor switch, Apple decided to change around some things in the whole boot-sequence realm.

In the days of the PowerPC chips (PPC). Mac-formatted drives used a formatting scheme called Apple Partition Map (APM) to format its hard drives. Open Firmware (OF) would recognize this volume type, and be able to boot to it. With the new Intel Machines, Apple scrapped the Open Firmware approach and went with Intel's Extensible Firmware Interface (EFI) to match the new chip. Along with EFI, there came a new partition scheme, the GUID Partition Table (GPT).

The OF of the PPC's (G3, G4, & G5) do not recognize GPT drives as bootable, meaning they can only boot to APM drives and the OS X for Intel installer insinuates the EFI of the Intel Macs will only work with GPT drives. This, along with the fact that there are two builds of OS X for PPC and Intel (8H14 and 8H1619, respectively), should mean that trying to use the same drive to boot both PPC and Intel macs will find you SOL.

In plain English, Apple wants you to believe that, just as, older Macs will only boot to the older, APM-formatted drives, the new Intel Macs will only boot to GPT-formatted drives. Fortunately, that's not necessarily the case.

A loophole

Interestingly enough, although the Intel Mac installation DVDs will only install the OS on GPT-formatted drives, it is possible to boot an Intel-based Mac to an APM-formatted drive. How do we know this? The installer DVD, itself, is APM-formatted. So where is the problem? To be truthful, we don't quite know. It is possible Apple implemented this to avoid problems installing the Intel version of Tiger on a PPC machine, or there may be another reason. But the possibility exists, we just need to get around the problem of the Installer preventing this process.

Why would you want to do this in the first place?

Before we get into the nitty-gritty of the whole process, you may want to consider why you would need to boot your Intel Mac to an APM drive, rather than just reformatting the drive into an Intel-specific GPT. While my main reasoning to try this less a matter of practicality than just the effects of large amounts of cough syrup and a dare, the main use most people will have for this would be using it to troubleshoot both Intel and PPC Macs. It becomes much more convenient to only carry one drive around, rather than two. It becomes even easier to transport such a troubleshooting drive around when it's a high-capacity OWC Mercury On-The-Go: One drive, two machine types, in your pocket. You can't get much more convenient than that, save for never having to use it in the first place.

Gather your materials.

The first thing to do is get all your pieces together. You will need:

  • A copy of OS X for PPC, and a Mac to run it on.
  • An Intel-based Mac, and its installation DVD
  • A nice, high-capacity FireWire hard drive.
  • Installers for your favorite diagnostic and utility software.
  • A good chunk of time and a little patience.

You don't need to worry about any special software to set up the drive itself, as everything you need to set up the drive is right in the OS.

Enough already! Get to it!

The first thing to do is prepare the drive. If you already have a troubleshooting drive set up, you have a couple choices. You can either clone the drive to a disk image using your favorite method and clone it back later (or just clone it directly to the drive, if you're setting up a brand new drive), or you can just start from scratch. Cloning the drive over is not covered here, as I have previously discussed various methods of cloning a drive in another article.

Once you have any data that was previously on your soon-to-be-dual-booting drive backed up or have otherwise accounted for it's loss, it's time to actually format the drive.

Formatting the drive.

Formatting the drive is as simple as a quick trip to Disk Utility. Simply attach your drive to a PPC machine and open Disk Utility.

Disk Utility

Once Disk Utility is opened, select the hard drive from the list of drives on the left. Then, since OS X has two versions (one for Intel & PPC), we will need to make two partitions. Simply go to the Partition tab, and select "2 Partitions" from the Volume Scheme menu.

Give each partition a name by clicking on the partition and then typing a name in the "Name" field to the right. I found that naming one "PPC" and one "Intel" differentiates them in a manner that will make them easy to recognize. You should also make sure that they are set to be formatted as "Mac OS Extended (Journaled)." Click the "Partition" button and wait a few moments. you now have two empty partitions.

Set up your PPC volume.

Now that we have the drive ready to have the OS installed on it, let's get the PPC side set up. If you already have another recovery drive (or cloned it to a disk image before reformatting your hard drive), you can clone it over (or back) to the PPC partition, and be done with it.

Otherwise, you will want to install a very pared-down OS onto the drive (turn off all the extra options in everything in the Customize menu except for "BSD Subsystyem" for older systems) and let it install.

Once you have the OS set up for use, install any of the tools you use when troubleshooting or fixing a system. Every person has their favorites, so your setup may be a bit different than mine. Spend a little time putting it together just how you like it. Once you have it done and are sure you can boot, its off to set up the Intel side.

Clone over the Intel volume.

This part is a little trickier. Since the OS X for Intel installer won't allow you to install onto an APM drive, we will need to clone it over from an existing install, namely from one of your Intel Macs. While it is most preferable to clone from a brand new install, as there are fewer added files, you can do this with any installation on your Intel Mac.

Boot the Intel Mac into Target Disk Mode by starting it up while holding down the "t" key. This will trick it into thinking it's just a really expensive FireWire drive. Connect the Intel Mac to your PPC computer via FireWire. The Intel's hard drive should show on the desktop. Now, it's time to copy. Normally, this would be a simple clone job, but all the clone tools I tried didn't work, causing the system to hang at startup. The only method that seems to work consistently is to use Apple Software Restore from the Terminal.

Copying in Terminal

Open up the Terminal program, and type in the following command, replacing the italicized names with the actual names of the appropriate hard drives:

sudo asr -source /Volumes/Intel Mac's drive name -target /Volumes/Intel partition name

Keep in mind that any spaces in a drive's name here needs to be preceded by a backslash ( \ ) in order to be recognized properly, so a drive named "Macintosh HD" would appear as " /Volumes/Macintosh\ HD " in the command.

Once you've entered this command, you will be prompted for an Administrator password. Once a valid password is entered, it will then copy the contents of your Intel Mac's hard drive to the Intel Partition. This can take a while. My 32GB installation (with apps and such) from my Intel to my external partition took over an hour to copy via FireWire, though your mileage may vary. You will get a message, though, when you have finished.

Once the data is copied, you may need to "bless" the system you just transferred over. This is done with another Terminal command. In the Terminal window that you just used to copy over the system data, type in the following command:

sudo bless -folder /Volumes/Intel partition name/System/Library/CoreServices

Once again, the same "backslash" issue described above applies here, as well. You may also be prompted to enter your admin password again. Once you do, you're all done with the Terminal.

It's ALIVE!!!!

At this point, you have a drive that is capable of booting your Intel Mac. Don't believe me? Try it. Hook the drive up to the Intel Mac and restart, holding down the Option key. You should see Intel partition listed as a bootable drive. Select that drive and watch as your Intel Mac boots to an APM-formatted drive!

Startup Disk

Or, if you prefer, boot to the Intel Mac normally, then open up the Startup Disk Preference Pane, and reboot from there.

Clean it up.

While booting from the APM-formatted drive is a fun little novelty, you will most likely want to make this drive useful and not just a trick to show at parties.

In all likeliness, your copy of OSX for Intel that was cloned over from your original Intel machine has a lot of extra applications that you probably will not need in a troubleshooting disk. Safari, iTunes, the World Book Encyclopedia, etc. are all nice to have, but they really won't help you determine what's ailing your computer, so you can take them out of your cloned system's Applications folder and chuck 'em into the Trash. We can do the same for your Documents - this is a troubleshooting disk, so you probably don't need Aunt Mildred's recipe for fig bars. Basically, the key here is to get rid of any apps you don't need that aren't part of the OS itself.

Import the importantMigration Assistant

Remember when we set up the PPC partition to have all our favorite tools and such? You spent quite a bit of time getting it how you like it, right? Fortunately, the time you spent on the PPC side can be applied to the Intel side, too. Once you've gotten rid of a lot of the "extra" stuff from your Intel partition (you're still booted to that one, right?), open up the Applications>Utilities folder and open the Migration Assistant.

Follow the steps in the Migration Assistant, importing everything from the PPC drive. Once you do, you should be able to set the transferred file as the default account in the Accounts Preference Pane. You'll get the layout from the old User folder and import all the Applications, as well.

Double trouble(shooting)

Provided that all your utility applications have been updated to Universal Binaries and/or are able to be used on an Intel Mac under Rosetta, you now will have a single hard drive unit capable of booting to either a PPC Mac or an Intel Mac and running any diagnostic software that may be needed.

How cool is that? :>)