Booting an Intel iMac from an External Drive
GPT replaces Apple Partition Map (APM) as the boot partition scheme for Intel-based Macs. And therein lies the rub. Intel-based Macs can’t boot from older APM drives, and PowerPC-based Macs can’t boot from newer GPT drives. This appears to be a permanent situation—each scheme makes incompatible assumptions about the layout of physical block 1 on the disk. While GPT was designed to be compatible with Master Block Record (MBR, the PC’s old partition scheme), it doesn’t play nicely with APM.
The main reason I haven’t switched over to using the iMac Core Duo as my main machine is that my DiskWarrior CD can’t boot it, and DiskWarrior can’t repair the internal drive using Target Disk Mode because of the new partitioning.
