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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: 80286 protected mode
Date: Mon, 7 Oct 2024 23:13:25 +0000
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References: <2024Oct6.150415@mips.complang.tuwien.ac.at> <memo.20241006163428.19028W@jgd.cix.co.uk> <2024Oct7.093314@mips.complang.tuwien.ac.at>
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On Mon, 7 Oct 2024 7:33:14 +0000, Anton Ertl wrote:

> jgd@cix.co.uk (John Dallman) writes:
>>In article <2024Oct6.150415@mips.complang.tuwien.ac.at>,
>>anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:
>>
>>> I find it hard to believe that many customers would ask Intel
>>> for something the 80286 protected mode with segments limited
>>> to 64KB, and even if, that Intel would listen to them.  This
>>> looks much more like an idee fixe to me that one or more of
>>> the 286 project leaders had, and all customer input was made
>>> to fit into this idea, or was ignored.
>>
>>Either half-remembered from older architectures, or re-invented and
>>considered viable a decade after the original inventors had learned
>>better.
>
> Here's another speculation: The 286 protected mode was what they
> already had in mind when they built the 8086, but there were not
> enough transistors to do it in the 8086, so they did real mode, and in
> the 80286 they finally got around to it.  And the idea was (like AFAIK
> in the iAPX432) to have one segment per object and per procedure,
> i.e., the large memory model.  The smaller memory models were
> possible, but not really intended.  The Huge memory model was
> completely alien to protected mode, as was direct hardware access, as
> was common on the IBM PC.  And computing with segment register
> contents was also not intended.

Is protected mode not "how Pascal" thinks of memory and objects
in memory ??

> If programmers had used the 8086 in the intended way, porting to
> protected mode would have been easy, but the programmers used it in
> other ways, and the protected mode flopped.

Whereas by the time 286 got out, everybody was wanting flat
memory ala C.

> Would it have been differently if the 8086/8088 had already had
> protected mode?  I think that having one segment per object would have
> been too inefficient, and also that 8192 segments is not enough for
> that kind of usage, given 640KB of RAM (not to mention the 16MB that
> the 286 supported); and with 640KB having the segments limited to 64KB
> is too restrictive for a number of applications.
>
> - anton