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Re: intel 386 et al

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On 11/09/2019 23:27, Paul Rubin wrote:
> Hul Tytus <ht@panix.com> writes:
>> 	Anyone know of a good handbook describing the machine code of Intel's 
>> 386's? A page describing each instruction along with some text about

I presume this is for some sort of history project?

> 
> I don't know if it's exactly the format you wanted, but I liked
> "Programming the 80386" by John Crawford and Patrick Gelsinger, who were
> involved with the 386's design.  It did a good job of explaining how
> memory mapping, the protected mode segment registers, call gates for
> crossing privilege domains etc. all worked.  I still don't understand
> why today's OS's don't use those features.  They would also allow
> application programs to be set up like miniature OS's with protected
> memory regions, for things like in-memory databases.
> 

It is a /long/ time since I have read details of the 386 - you are
talking about a processor that was outdated over 25 years ago.

However, if my memory and understanding is correct, many of these
advanced protection features were overly complex and extremely slow.

In the days of the 386, there were four main classes of operating
systems for it.  One was DOS - still popular.  Since MS at the time had
close to zero concern for security or reliability, it used very little
of the protection features, or memory mapping abilities.  It did not
even use 32-bit modes very much (32-bit DOS extenders were made by third
parties).  Then there was early Windows.  Again, security and protection
were not a concern for MS, though they used a couple of features to get
multi-tasking of DOS programs.  Then there was *nix type systems.  These
simply did not need the call gates and other bits and pieces for
security - all they need are a distinction between user mode and kernel
mode, and a way to switch between them.  And they didn't need any
"virtual" modes or other complications that the 386 provided to let you
use old binaries on newer protected systems - you just compiled your
*nix code anew for the new system.

The complexities of the call gates and other features of the 386 were
concepts from a bygone era by the time the 386 came out, and were never
of use in the kind of systems used by the 386.  And they have no use now
either - modern protection rings and hardware virtualisation are
massively more efficient, as well as being simpler and more flexible.

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intel 386 et al Hul Tytus <ht@panix.com> - 2019-09-11 21:06 +0000
  Re: intel 386 et al Paul Rubin <no.email@nospam.invalid> - 2019-09-11 14:27 -0700
    Re: intel 386 et al David Brown <david.brown@hesbynett.no> - 2019-09-12 10:37 +0200
      Re: intel 386 et al "Mat Nieuwenhoven" <mnieuw@zap.a2000.nl> - 2019-09-13 11:37 +0200
        Re: intel 386 et al David Brown <david.brown@hesbynett.no> - 2019-09-13 12:31 +0200
      Re: intel 386 et al George Neuner <gneuner2@comcast.net> - 2019-09-16 14:57 -0400
        Re: intel 386 et al Robert Wessel <robertwessel2@yahoo.com> - 2019-09-17 01:01 -0500
          Re: intel 386 et al upsidedown@downunder.com - 2019-09-17 09:40 +0300
          Re: intel 386 et al George Neuner <gneuner2@comcast.net> - 2019-09-17 17:51 -0400
            Re: intel 386 et al Robert Wessel <robertwessel2@yahoo.com> - 2019-09-17 21:43 -0500
    Re: intel 386 et al Hul Tytus <ht@panix.com> - 2019-09-12 20:28 +0000
  Re: intel 386 et al Herbert Kleebauer <klee@unibwm.de> - 2019-09-12 09:14 +0200
  Re: intel 386 et al Stefan Reuther <stefan.news@arcor.de> - 2019-09-12 18:42 +0200
    Re: intel 386 et al Hul Tytus <ht@panix.com> - 2019-09-12 20:33 +0000

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