Subject: Re: DMA beyond end of isa
To: Jeff Northon <jeffo@sasquatch.com>
From: Peter Galbavy <peter@wonderland.org>
List: port-i386
Date: 12/28/1995 19:15:44
> > And everyone has an EISA motherboard ? Yeah, sure. I have real ISA
> > motherboards, not even local bus...
> 
> So just recognize that you can use up to 16 megs of memory on ISA.

If you want to get into a technical argument please make sure you are
working from a strong foundation based on fact. The ISA architechture
can address up to a 16Mb address space. There is no limit on memory
unless you want to put your memory onto an ISA card. Typically the
memory is tightly coupled to the CPU and the bus is accessed as part
of the lower 16Mb address space of the CPU. The fact that ISA cards
that do bus mastering DMA can only do this DMA in/out of the lower
16Mb of addressable space does not mean that bounce buffers are not
a solution in this environment.

> Don't be so stupid. I was using this as an example of the 16 meg
> limit on ISA.

But this is what the thread is about. You are not going to be able to
limit people to only use 16Mb of RAM in an ISA bus system because you
think they should upgrade. They will get an OS that works for their
hardware.

> > Next you will be telling us to get rid of the amiga/sun4c/etc ports
> > because they don't make that hardware anymore ?
> 
> Hey people still take 1957 Chevies and make hot rods out of them
> and Chevy doesn't make them anymore.

I don't drive so this analogy is meaningless to me, but I understand your
point of view here. The fact is that I like Sun IPX systems and these
quite obsolete pieces of hardware. Because Sun have effectively halted
support for their BSD based OS (4.1.4) I need an alternative. My IPX and
SS2 systems are quite powerful enough to saturate an Ethernet and SCSI
bus (not fast SCSI unfortunately) and the graphics performance is far
suppierior to my local bus based 5428 card. I like doing it this way.

When a major vendor adopts one of the free OSes as their OS of
choice then your analogy may apply, but for now we are all "amateurs"
at this, and are building and maintaining this stuff in our garages.

Of course I have ignored the fact that at work we use slightly over
spec-ed Pentium PCs as routers and they work very well. If we had
100BaseTX support for our Ethernet switches then we could actually
start using Matt Thomas' excellent driver for what it was intended
:-)

Regards,
-- 
Peter Galbavy                                           peter@wonderland.org
@ Home                                                 phone://44/973/499465
in Wonderland                              http://www.wonderland.org/~peter/
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