As part of GSoC I need to get an easy tool to create boot able usb sticks from Intel Macs. This past week I've been investigating how Macs do boot. In the process I've wiped my partition table, recovered using testdisk , plaid around with rEFIt, mac boot options, NVRAM, efi shell read tons of apple source code , and UEFI specs . Overall it's quite complex and fun =). I'll try to document as much as possible of everything I have found out in the rest of this post. On power-on, BootROM is doing Power-on-Sefl-test and hands over to OpenFirmware on PowerPC machines, or to the EFI bootmanager (as far as I understand) on Intel Macs. The BootROM "knows" about the fancy startup keys, e.g. options key which can passes hints to OpenFirmware & EFI bootmanager on what user wants to do (e.g. clean NVRAM & PRAM, force pop-out cd, perform target-disk mode boot, netboot or present available boot drives). OpenFirmware later on passes onto BootX and that boots OS 9 ...