17 Oct
2012
17 Oct
'12
6:42 p.m.
On 18 October 2012 02:08, David Riley <fraveydank at gmail.com> wrote:
On Oct 17, 2012, at 5:18 PM, Liam Proven wrote:
Ah, yes. So: the S-100 bus only allows for 24 bits of address, but
many things you'd like to run on a 386 (BSD, etc) are happy to run
well beyond that. So, like the MicroVAX of yore (a VAX system which
ran on QBUS, which only had 22 address bits), they've opted to add
an alternate side bus for memory to allow for a full 32-bit address
space for RAM.
So yes, a 386SX would be a perfect match for S-100 in principle,
but if you wanted to take advantage of the 32-bit address space
of the 386, you might want to go with a DX and an alternate RAM
solution.
Well, yes, I got that (although I didn't know that detail about VMS) -
it just seems a lot of extra work for a hobbyist project. But what do
I know about such things? Nothing, clearly!
TBH, in terms of low-end OSs that would work well on a 386, 16MB is a
lot. You could run Linux or NetBSD happily in that. Probably even
Linux 3.2 if carefully compiled.
As has already been discussed, implementing VGA on an S100 board is
non-trivial. The machine is not likely to be running Windows 2000, and
indeed, on a 26 year old CPU, it won't be running any full modern OS
whatsoever.
(Yes, the 80386 was 26y ago. 1986. Sheesh. I remember it being the big
new thing, the great white hope for the PC.)
--
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in which
case it's a limit of the S-100
bus and not the 386 in question.
... just that, the 16MB limit, then I thought "why not use the smaller
cheaper simpler version of the 386 that only *supports* 16MB and has
half as many legs to solder, half the bus width and so on." It seemed
an obvious question to me; if one is building an S100 computer, and
that means no more than 16MB, then use the easier chip that only
supports 16MB.