ISA bus limitations...

[Dick Dunn]

tmh at keks.FOKUS.GMD.DBP.DE (Thomas Hoberg) writes:
> ...rcd at ico.isc.com (Dick Dunn) writes:
...
> |> Somewhere along the way to moving memory off the ISA bus, someone should
> |> have come up with a better DMA controller that also had a way to get to
> |> more memory.
...
> ...But no DMA controller, however smart, can
> circumvent the fact that there are only 24 address lines on the ISA bus.

That's true, but that's not what I meant.

Once again, memory doesn't go on the ISA bus.

Since the DMA controllers go on the main board, in theory they could have
access to the (private, non-ISA, >24-bit) memory bus, and one could imagine
a design which would give them access to the ISA bus on one side and memory
on the other, so that they could handle transfers in/out of full memory.

(That's a theoretical argument.  It would have had to happen much earlier
for it to work...in a practical sense, it's too late for that to happen on
ISA-based machines, so EISA seems to be the answer.)
-- 
Dick Dunn     rcd at ico.isc.com -or- ico!rcd       Boulder, CO   (303)449-2870
   ...Mr. Natural says, "Use the right tool for the job."