Re: Address bits again, Article on new mainframe use

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.