i'll just reply to this one, but thanks to all who replied!

> > I don't know exactly if the 2 backplanes differ.
> The older /300 only backplanes have a 32 bit memory interconnect, the
> newer /300 and up backplanes have a 64 bit memory interconnect. I have
> a /300, that was upgraded to a /400 with the 5019353 / 5419354
> backplane. But remember that the /400 CPU uses different memory (32 vs.
> 64 bit). 

yeah, i know about the memory being different, i just needed to know if i have
a /300 with the proper backplane to be able to use this CPU.  now i know what
to look for, thanks!

-brian