CJ
Ok, there are a lot of other things that could be different, but it is a possibility that IBM and AMD are using a very similar, if not identical, process at 90nm. It would make sense if they were as close as possible so that AMD could fab out certain parts even at 90nm.
Toosets of Fab30 (200mm) and East Fishkill (300mm) are significantly different and process different wafers as well, not only in size.
But then, AMD talked of a "second-generation 90nm process recently." Could easily be a 300mm 90nm process to be developed in East Fishkill by the joint team, as a bridge to their common 65nm process if you want.
K.