The partition does not have to be marked as active either because Mac's EFI simply scans ALL partitions and displays the ones that have /System/Library/CoreServices/boot.efi if you hold down 'option' during startup. Remember, EFI is just loading a bootloader out of a file so we aren't limited to only booting primary partitions. The partition that the files are on can be either a primary partition or a secondary partition. It doesn't matter whether the drive is structured as MBR structuring or if it is structured with the GPT structuring. So EFI in this situation makes life very easy. It just has a file at /System/Libray/CoreServices/boot.efi which can be detected and listed as an option to boot into when you hold down 'option' during startup and have the DVD inserted. Any partition that has that file shows up and you can chose to boot from it.Ī Mac OS X install DVD, to my knowledge, doesn't even use the El Torito boot specification.

When you hold down 'option' it scans all partitions for /System/Library/CoreServices/boot.efi. That's right, the system firmware can actually load a bootloader out of a file!

Here we have EFI which looks for a file containing a bootloader in /System/Library/CoreServices/boot.efi. The reason why it's so easy (just copy & paste) is because you don't have to install a bootloader to the disk in the traditional sense, which would have to be 'raw-written' to certain sectors (or one sector). All you have to do is copy all the files (even the hidden ones) from the DVD onto a partition formatted as HFS+, or some other filesystem that can do symlinks (symbolic links, which are shortcuts that look like the actual file rather than a shortcut).

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