Originally posted by gopher
You can count on 10.4 to only run on G4s and G5s. The 10.3 milestone was reached by saying it could only run on new world ROM machines. The next major advancement in Apple's hardware architecture was the switch to G4s. I'm sure there will be people upset about it, but it seems inevitable that at some point they will drop G3s. Doesn't mean your G3 isn't a perfectly good machine, but Apple has to draw the line somewhere, otherwise overtax its support staff.
Other people have already addressed the "what about the iBook?" rebuttal here, but there's another thing too: as far as the user was concerned, I suppose the G4
was the next major advance, but it came at the same time as another big change that is (AFAIK) more important when it comes to OS support: the introduction of the Unified Motherboard Architecture (Uni-North + KeyLargo). I believe the first UMA-equipped products to be announced were the original iBook and the slot-loading iMacs, followed shortly by the Power Mac G4 (AGP Graphics) and finally, a few months later, the PowerBook G3 (FireWire). Trying to squeeze all that information into a System Requirements thing on the box might be a bit tough--there are essentially no external differences between the Power Mac G4 (PCI Graphics) and the Power Mac G4 (AGP Graphics)*, but the latter would be compatible with 10.4/whatever while the former would not. But I'm sure Apple could figure it out.
Of course, I'm biased towards the UMA rather than the G4 being the next minimum requirement, because I own one of the slowest UMA-equipped Macs (clamshell iBook).
I notice that some people think built-in FireWire will be the next cutoff. Y'all are confusing features with architecture. Adding FireWire to the iMac and iBook didn't mark a change in architecture, nor was the architecture of the FireWire-equipped B&W G3 much (if at all) different from that of the non-FireWire-equipped Lombard PowerBook.
I'm biased here too, because my iBook doesn't have FireWire either.
It
is kind of curious that built-in FireWire is required for DVD playback in OS X, but I think this was the easiest way for Apple to specify that it requires at least a Rage 128 (all non-FireWire-equipped systems have Rage II's or Rage Pro's or similar GPUs).
WM
* The AGP one has the audio in/out ports in a different configuration (horizontal vs. vertical) and its FireWire ports are spaced much further apart.