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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: Privilege Levels Below User
Date: Thu, 13 Jun 2024 23:48:14 +0000
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Paul A. Clayton wrote:

> On 6/8/24 1:37 PM, MitchAlsup1 wrote:
>> EricP wrote:
>> 
>>> Scott Lurndal wrote:
> [snip]
>>> What they found that not only do they not need 4 levels,
>>> it was a pointless overhead to have to constantly switch between them.
>>> (There is a pretty high penalty to switching modes, copying in args,
>>> validating args, doing something usually simple, then switching back,
>>> when it is all the OS's code anyway.)
>> 
>> VAX was before common era Hypervisors, do you think VAX could have 
>> supported secure mode and hypervisor with their 4 levels ??
>> 
>> But for similar reasons ring 1 and 2 are not used in x86 machines, 
>> either. {{NOw, if we could just go back to 1982 and not invent 
>> IDTs, and call gates, .....}}

> I thought My 66000 had Port Holes that are vaguely similar to
> call gates, so rather than "not invent" perhaps invent with better
> semantics and a better interface?

I would place them congruent to Load-From and Store-TO PDP-11/70
instructions.

I have since converted to a more Linux friendly MMU structure.
Port Holes can be easily resurrected.

>                                    (Though 1982 might have been too
> early to implement such. Better perceiving when to wait for the
> technology or understanding to implement something better is
> presumably one of the skills acquired by long experience as well
> as the related what can be implemented to provide the most
> attractive/marketable features without excessively limiting future
> developments. 


>              Letting a competitor provide a temporarily better
> product — or delaying entry into a market expecting a feature —
> can sometimes be sensible if one expects to leapfrog with
> a better long-term alternative, but "worse is better" has some
> truth.)

It seems that in terms of computer architectures, the world is
not going to beat a path to your door even if you invent a
better mousetrap.