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NNTP-Posting-Date: Fri, 20 Dec 2002 13:23:58 -0600
Date: Fri, 20 Dec 2002 13:26:24 -0600
From: gary drummond
X-Mailer: Mozilla 4.78 [en] (Win98; U)
Subject: Re: Which basic compiler to buy?
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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
I think it was an 8088 at first...
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