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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: Address bits again, Article on new mainframe use
Date: Thu, 12 Sep 2024 20:48:41 +0000
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On Thu, 12 Sep 2024 20:15:01 +0000, John Levine wrote:

> According to Michael S  <already5chosen@yahoo.com>:
>>x86 Real mode segmentation is a hack to the address space. 80286
>>protected mode segmentation is something else. The only similarity
>>between the two is maximal size of segment is the same.
>
> The 386 had 32 bit segments which should have made segmented code
> practical and efficient
> and allowed giant programs with lots of gigabyte segments. But Intel
> shot themselves in
> the foot. One problem was that loading a segment register to switch
> segments remained
> extremely slow so you still needed to write your program to avoid doing
> so.
>
> The other was that they mapped all the segments into a 32 bit linear
> address space, and
> paged the linear address space.  That meant that the total size of all
> active segments
> had to fit into 4GB, at which point people said fine, whatever, set all
> the segment
> registers to map a single 4GB segment onto the linear address space and
> used it as
> a flat address machine.

Intel's only other choice was to use more than 32-bits as the segment
base address and they had run out of bits.
>