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From: Keith R. Williams
Subject: Re: Which basic compiler to buy?
Date: Wed, 18 Dec 2002 12:16:15 -0500
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
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In article , firstname.lastname@example.org says...
> "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.
Not true. Programs larger than 64K were very easy to write (FAR
calls). Single *data* structures larger than 64K were somewhat more
complicated, but not all *that* difficult.
> 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.
I don't understand this at all! The biggest impediment was the hole in
the middle of the memory map (memory from 0A0000 - 0FFFFF) used for I/O
> 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.
Sure, but hardly important to the issue at hand.
> 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
How are you going to "switch out" the hardware that was located in that
range? That couldn't have been a 100% ccompatable.
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