> Well, the exception arrangement requires RAM starting from the physical > address 0. It seems natural to place RAM just there, avoiding additional > complexity to address decoders. But then firmware has to be somewere > around 0x1fc00000, so to support more than 508MB of RAM the designers > would have to create a hole in RAM, which would have to be handled by the > OS then. Thus abandoning the idea of putting RAM low, placing it > somewhere above 0x1fffffff and just mapping some of it at 0 for the > exceptions seems a better solution. OK, I forgot about the firmware placement. Why didn't they move it to somewhere else when booting 64-bit? (A rhetorical question, I know.) I would place some fixed code there. Or a different memory, maybe 16 kB of static RAM so it will always be fast. With what is now, we have physical and virtual aliasing and it's all a bit like a > Fortunately everything is not a PC. :-) Yes, fortunately. The 386 memory management is a joke. The BIOS in the middle is an even darker joke. Well, in my opinion the R8000 was right in not having compatibility segments. Stanislaw
