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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: Address bits again, Article on new mainframe use
Date: Fri, 13 Sep 2024 23:20:27 +0000
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On Fri, 13 Sep 2024 17:47:01 +0000, George Neuner wrote:

> On Wed, 11 Sep 2024 18:24:24 -0700, Lars Poulsen
> <lars@beagle-ears.com> wrote:
>
>>On Wed, 11 Sep 2024 21:34:25 +0000, MitchAlsup1 wrote:
>>>> I am not a fan of segmentation ...
>>
>>On 9/11/2024 4:45 PM, Lawrence D'Oliveiro wrote:
>>> Big segments versus small segments are quite different things.
>>
>>Segments do different things. The aspect of segments that I liked in the
>>80286 was that they provided an excewllent mechanism for array bounds
>>checking. I would have loved having that option within a linear, paged
>>address space. But the languages in wide use at the time did not support
>>that.
>
> One (of many) problem with 286 segments was that there simply were not
> enough available to be really useful.  You need enough for every
> object in the program.

The modern way to state this is that:: "You need an unbounded number
of segments"

> Intel had the opportunity to do segmentation much better with the 386,
> but they fumbled it badly: too slow - and no more segments possible
> than with 286.

Segments are one thing that is exceptionally hard to virtualize,
especially when you have an unbounded number.