Hmmm, what's all this buzz over at Mac OS Rumors about the iMac possibly having PCI expansion capabilities? Apparently the little blue lump does in fact rely on the PCI bus in order to shuttle data between the main processor and the USB and graphics subsystems. That's an intriguing bit of information, especially for those of us who would love to see some kind of hack that could allow a PCI expansion chassis-- even a single-slot one-- to connect to the iMac. And as Rumors supposes, some kind of passthrough card that sits between the motherboard and the processor card might allow just that, if some third-party company were clever enough to come up with such a thing.

Of course, that point is moot if the shipping iMacs retain the special proprietary slot that existed in at least some of the preproduction models. Remember the first iMacs that got dragged around from users' group to users' group? Those models had external monitor ports peeking out through a knockout panel in the iMac's port bay. While it's been widely reported that shipping iMacs will not have the capability to drive an external monitor (the ports on the demo units were there to allow the connection of a projection module, making demos easier to give), we sincerely doubt that Apple would actually remove whatever architecture it used to attach the extra video circuitry to the motherboard. That circuitry is reportedly a custom-pinout proprietary PCI expansion slot.

Indeed, all of the iMacs AtAT used at the MacWorld Expo still had a knockout panel in the port bay, implying the existence of an expansion slot behind it. None of them had a monitor port installed. And while those iMacs were still preproduction models, we strongly suspect that the shipping systems will still have a proprietary and unpublicized expansion slot on the motherboard. But if so, why is Apple keeping mum about it? Is it for legal reasons? After all, if they won't market the iMac as "processor-upgradeable" because no one may ever sell a processor upgrade for it, mightn't they also balk at calling the system "expandable" as well? Very interesting... We can't wait until the iMac actually ships to see what changes, if any, were made to the original motherboard.