From: "Michael A. Terrell"
Subject: Re: Which basic compiler to buy?
Date: Fri, 20 Dec 2002 22:10:26 -0500
Organization: Have you seen my bench? No, really! Where is it?
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Tom MacIntyre wrote:
> On Fri, 20 Dec 2002 13:26:24 -0600, gary drummond
> >Tom Del Rosso wrote:
> >> "Tom MacIntyre" wrote in
> >> message news:email@example.com...
> >> > >
> >> > >To be fair, IBM's hardware set the memory limit.
> >> > >
> >> >
> >> > But wasn't DOS still incapable of exceeding the 640k long after the
> >> > hardware support was there?
> >> That was mostly because of Intel's hardware goof. Their segmented
> >> memory made it necessary for any program of more than 64k to do a lot of
> >> address arithmetic, and that made it hard to migrate to a different
> >> system with more segments. DOS couldn't really have been designed with
> >> enough foresight to have been portable to the 286 memory model. Intel's
> >> data on the 8086 didn't say a word about planning for the segments
> >> becoming virtual, so the natural assumption was that consecutively
> >> numbered segments were consecutive. In fact Intel encouraged that
> >> assumption when they explicitly stated that segments and offsets could
> >> be added different ways, for example the way 0040:017A = 0000:057A.
> >> Getting back to IBM's goofs, the original DOS made by a small company
> >> which sold it to MS, had 1 meg of RAM, because they used a little 8086
> >> system that could switch out the ROM! I don't know who made that
> >> system.
> >I think it was an 8088 at first...
> Memory may let me down again, but the 8086 was first, and they cut it
> back on the external bus in the 8088. Anyone?
Yes, the 8086 was first. The 8088 was a 8 bit buss version to allow
the 8086 core to be used in cheaper designs. The original PC design was
a close copy of the example design in the early Intel books, modified to
use existing 8 bit cards.
Michael A. Terrell