Jonathan Rentzsch: 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 … Continue reading Booting an Intel iMac from an External Drive