Putting two OSX's on the one drive...

Question

I have just bought a macbook pro and still have my Powermac G5 and am now straddling the intel/powerpc fence.
I have an external firewire drive that I use as a diagnostics drive on which I have installed OSX and a couple of troubleshooting apps (diskwarrior and techtool pro primarily).
Now I think I'm going to need both intel and powermac installs of the OSX... What I'm wondering is.. can I do it without partitioning the drive?
Chris

Answer 1

Apparently, even though Apple doesn't say it is supported, Intel Macs can boot from an Apple Partition Map (APM) partition scheme. (This was discovered when some folks noticed Intel iMac DVD disks used the APM scheme.) PPC Macs cannot boot from a Partition Table (GPT) partition scheme. Some people have had success exploiting this 'dual boot' nature of Intel Macs to make a universal boot FireWire drive using the APM scheme.
This usually involves repartitioning the drive with two OS versions (Intel & PPC), each on its own partition. (Some ambitious souls have managed to make "universal" OS versions that avoid the two partition requirement, but this has some undesirable consequences, so avoid it if you can.)
The general idea is straightforward:
1. Use Disk Utility's "Partition" tab to format the Firewire drive in the APM scheme, creating two HFS+ partitions (the drive will be completely erased).
2. Boot from a PPC Mac & install 10.4.x on one partition, using a PPC install disk.
3. Reboot from an Intel Mac & install 10.4.x on the other partition, using an Intel install disk.
The "extraordinary measures" come in at step 3, because the Intel installer won't let you install the Intel version of the OS on an APM scheme drive. The workaround is to restore the Intel OS version to the partition using Disk Utility's "Restore" tab. Probably the best way to do this is to install a fresh copy of the OS to an internal partition of an Intel Mac (or to any GPT partition), make a disk image of it, & use that image as the restore source.
In theory, you should be able to use cloning software to copy your working Intel install to the second partition, but this doesn't seem to be an approach anybody has discussed much.
However you do it, you will have to select the correct version of the OS at startup (using the Option key, for instance) for each mac. If you try to start up an Intel Mac with the PPC version of the OS or visa versa, the Mac will crash. This doesn't harm anything (or so they say), but to keep things simple, name each volume with something distinctive (like "PPC Boot" & "Intel Boot"), since your startup choices won't necessarily tell you which is which.
Note that I haven't personally tried this, only read about it (since I will someday want the same capability). Mention of the technique first appeared about a year ago but I have seen nothing since to suggest it still isn't viable. To be on the safe side, check your Intel DVD disks to see if they are APM, which should be a good indication that your Intel Mac will boot from the hybrid FireWire drive. (In Disk Utility, select it & its partition scheme will be shown at the bottom of the window.)
You can read more about this technique at (for example) rentzsch.com: Intel-based Mac Boot Incompatibility or Macs on Intel: Boot Issues. An interesting variation on the universal OS approach can be found at macosxhints.com - 10.4: Create a single Universal binary bootable disk.