There's a man page with the linux utility ybin (Yaboot bootloader 
installer) that describes the boot process. It's long and includes 
oldworld stuff but I found it to be useful in understanding how OF 3 
works

I have an iMac DV (First gen) so I guess I'm using OF 3.

OF tries to load the file referred to by boot-device.

eg hd:,\\:tbxi

This tells OF to look for a Blessed Folder on the hard disk (first 
available partition) and to load a file with file type tbxi (MUST be 
a CHRP script)

MacOS will bless a folder that contains a system briefcase and a valid Finder.

you can get small hacked copies of these to fool MacOS into thinking 
that your folder is macos and it will get blessed.

I got these files from a LinuxPPC 2000 CD. I put them on a small 
partition with a file of type tbxi. (the name of this file is not 
important)

Apple_Bootstrap means that the filesystem is HFS but that MacOS 
shouldn't mount it. if OS X is installed on UFS, then a HFS partition 
is needed because OF will only boot from HFS, HFS+ MS-DOS, ISO9660. 
(My machine can boot the NetBSD 1.5_Alpha2 CD)

MacOS X uses Apple_Bootstrap or something else as it's partition type 
so that MacOS won't see it and unbless it's folder.
This is why if you install MacOS X onto HFS+ you need to use System 
Disk to select which disk to boot from. MacOS X doesn't have fake 
system and Finder files so if you boot MacOS 9 it makes the OS X disk 
unbootable (System disk will override it)


The file Mac OS ROM is a CHRP script (open it in BBEdit)
The Program BootX for MacOS X is a CHRP script
They both have code inserted after the script


I have a boot menu that lets me chose which OS to load. It is a CHRP 
script based on what ybin creates
This is how I boot several OSes

boot hd:8,\boot\yaboot
boot hd:10,\\:tbxi
boot hd:9,\\:tbxi
boot hd:13,\System\Library\CoreServices\BootX
boot cd:,\\:tbxi
boot enet:0

Hope that helps people...

Link :)
-- 

------------------------------------------------------------------------
Lincoln Ramsay                                  <mailto:lramsay@mac.com>

     Beware of worshiping Jesus as the Son of GOD and professing your
     faith in Him as the Savior of the world, while you blaspheme Him
     by the complete evidence in your daily life that He is powerless
     to do anything in and through you.
         -- Oswald Chambers