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From: Brett <ggtgp@yahoo.com>
Newsgroups: comp.arch
Subject: Re: 80286 protected mode
Date: Mon, 7 Oct 2024 17:40:04 -0000 (UTC)
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Michael S <already5chosen@yahoo.com> wrote:
> 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.
>> 
> 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.

Today the 8088 is a joke microcontroller, that was not the case when it was
introduced. The 8088 was a major project with major profits, not some
afterthought.

Yes the success eventually dwarfed expectations, but that was a lightning
strike, the plan was in place and so the lightning strike could be taken
advantage of to build a monopoly, instead of the small walled fortress with
moat that was planned.

You saw what happened to the MC680x0 series that did not have a moat or a
good plan.