mjg59: "For an HFS+ filesystem, the inode of the bootloader is written to a specific offset in the filesystem superblock and the firmware simply finds that inode and executes it. And this appears to be all that older Macs support." Not entirely true. On HFS+ inodes are actually special files in "\0\0\0\0HFS+ Private Data" (the joy of forcing non-POSIX filesystem into POSIX world). What's written in superblock is catalog node id and converting it to actual extents involves btree lookup, so I wouldn't say it's simple.