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From: Michael S <already5chosen@yahoo.com>
Newsgroups: comp.arch
Subject: Re: 80286 protected mode
Date: Mon, 7 Oct 2024 20:03:35 +0300
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On Mon, 7 Oct 2024 16:32:34 -0000 (UTC)
Brett <ggtgp@yahoo.com> wrote:

> Anton Ertl <anton@mips.complang.tuwien.ac.at> 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.
> > 
> > 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.
> > 
> > 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.  
> 
> I have for decades pointed out that the four bit offset of 8086
> segments was planned obsolescence. An 8 bit offset with 16 megabytes
> of address space would have kept the low end alive for too long in
> Intels eyes. To control the market you need to drive complexity onto
> the users, which weeds out licensed competition.
> 
> Everything Intel did drove needless patentable complexity into the
> follow on CPUs.
> 
> > - anton  
> 
> 
> 

You forget that Intel didn't and couldn't expect that 8088 would be
such stunning success. Not just that. According to Oral history they
didn't realize what they have in hands until 1983.