so over the past couple weeks I have been playing with Mac OS 8.6 and i figured id just post my findings so to start the Mac OS 8.6 image im working with here is the as far as i know the last 8.6 image apple put out which was the image for the Sawtooth. now my goal with it was to try and get it running on computers that shipped with 9.x so with that said here is what I found out. The Mac OS ROM included with this image of 8.6 is different to later Mac OS ROMs in that it has a much more specific machine check that is run when loading from OF then later Mac OS ROMs (and in OS Xs BootX for that matter) see when the Mac OS ROM image or BootX is loaded in OF they run a small script at the start to check the "compatible" property in the Root of the open firmware device tree. now later Mac OS ROM images and BootX check just for the MacRISC, MacRISC2, MacRISC3 or MacRISC4 compatible property. but this image of Mac OS 8.6s ROM image has a much more specific check in that it has a list of compatible Model identifiers in the compatible check rather then just a Generic overall machine class compatible check. so instead of checking if Just MacRISC or MacRISC2 is there it has a list of model IDs it checks for. and the machine IDs it checks for before counting to load if found or aborting if not found are. iMac,1 PowerMac1,1 PowerBook1,1 PowerMac2,1 PowerMac3,1 PowerBook2,1. so on any of the machines the Sawtooth image of 8.6 would boot up fine. but if say you tried to boot it on a PowerBook G3 Pismo it would abort as it would go to check the compatible listing in OF and pull up PowerBook3,1 and abort as thats not in the compatible list. now I had to get around this the easiest way to do this was simply to change the PowerBook3,1 listing in the compatible property in OF to PoweBook2,1 for that boot session (it is possible to make it persistent but thats for another time) so I did that and it low and behold Mac OS 8.6 started to boot on the Pismo however near the end of booting from the installer CD the machine would just turn off without warning so I took the HDD and manually installed 8.6 to the HDD and re did the above steps this time booting from HDD and it booted all the way to the desktop. I got 8.6 running on an unsupported and newer computer then it self a couple quirks with it is it does not detect the battery (tho it runs off battery fine) and the Rage 128 drivers dont load (this one is probably solvable by installing newer ATI drivers) and finally another interesting thing I noticed was with a normal 8.6 install 8.6 does not recognise a 7410 CPU Properly but this sawtooth image on my Pismo has no problems knowing what to call the 7410 that I have fitted. (which is interesting as the 7410 had not yet come out when the Sawtooth went on sale but i would not be surprised if apple was already playing with engineering samples or the like) I hope this all makes sense (im not very good at making proper forum posts ) its not meant to be a guide or anything just a post on my findings and that it is possible to boot Mac OS 8.6 on unsupported/newer Macs (I did try this on a 800Mhz Snow iBook G3 and it did not get very far before hanging sadly.) and I may go into greater detail in what i did at a later point.