x86 - why unite when you can fragment?

By: Konrad Schwarz (no.spam.delete@this.no.spam), March 17, 2021 10:19 am
Room: Moderated Discussions
Linus Torvalds (torvalds.delete@this.linux-foundation.org) on March 14, 2021 4:58 pm wrote:
> Andrey (andrey.semashev.delete@this.gmail.com) on March 14, 2021 4:15 pm wrote:
> >
> > In the FRED model, I'm kind of alerted that they are dropping rings 1 and 2, basically leaving
> > kernel and userspace with nothing in between. This fits Linux and Windows needs, but I wonder
> > if that would be limiting for other designs, like microkernels? What was the intended use case
> > of the middle rings if not some semi-privileged stuff like some drivers and system services?
>
> The middle rings were always completely and entirely useless.

I believe the thinking behind the four rings was in a similar vein as the iAPX432:
hardware should provide richer semantics to enable e.g., finer grained protections.

I think this was inspired by Multics, which used dynamically mapped memory
segments and (I assume) had a dynamic linking facility. (Obviously,
it was also a natural/hackish outgrowth of the segment registers required by the
8086 to address 1 MB).

In contrast to the "simple" Unix process/kernel split, you would be able
to create a rich, integrated system (in the 286 without separate address spaces),
with micro-kernel-like servers.

However, this never panned out in practice (think OS/2, 16-bit Windows, which AFAIK
didn't use the four rings anyway), and it turned out that the dumb Unix model was
good enough and much more robust, and if you really wanted to, you could move drivers
to user space and use IPC to talk to them.

It turned out that software can emulate any rich semantics that you would like
and that transistors were much better spent making the machine as fast as possible.
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TopicPosted ByDate
x86 - why unite when you can fragment?anonymou52021/03/12 06:16 PM
  x86 - why unite when you can fragment?Linus Torvalds2021/03/13 01:18 PM
    x86 - why unite when you can fragment?Jon Masters2021/03/13 07:25 PM
      x86 - why unite when you can fragment?Jon Masters2021/03/13 07:44 PM
        x86 - why unite when you can fragment?Yuhong Bao2021/03/13 08:49 PM
        x86 - why unite when you can fragment?tt2021/03/20 09:30 AM
    x86 - why unite when you can fragment?Andrey2021/03/14 04:15 PM
      x86 - why unite when you can fragment?Linus Torvalds2021/03/14 04:58 PM
        x86 - why unite when you can fragment?anonymou52021/03/14 05:31 PM
          x86 - why unite when you can fragment?anon22021/03/14 08:07 PM
        Microkernel?Anon2021/03/14 11:49 PM
          Microkernel?none2021/03/15 12:37 AM
            Microkernel?Anon2021/03/15 01:56 AM
          Microkernel?anon22021/03/15 01:58 AM
            Microkernel?Simon Farnsworth2021/03/15 03:12 AM
              Microkernel?anon22021/03/15 04:53 AM
                Microkernel?Simon Farnsworth2021/03/15 06:56 AM
                  Microkernel?iz2021/03/15 08:10 AM
                    Microkernel?Anon2021/03/15 09:05 AM
                      Microkernel?iz2021/03/16 01:25 AM
                        Microkernel?Andrey2021/03/16 02:54 AM
                          Microkernel?iz2021/03/16 08:36 AM
                            Microkernel?Andrey2021/03/16 10:06 AM
                              Microkernel?anonymou52021/03/16 11:44 AM
                              Microkernel?iz2021/03/21 02:58 AM
                                Microkernel?Andrey2021/03/21 09:34 AM
                  Microkernel?anon22021/03/15 08:31 AM
                    Microkernel?Simon Farnsworth2021/03/16 04:42 AM
            Microkernel?Gabriele Svelto2021/03/15 03:21 AM
              Microkernel?anon22021/03/15 04:56 AM
                Microkernel?Gabriele Svelto2021/03/15 10:41 AM
                  Microkernel?anon22021/03/15 08:00 PM
                    Microkernel?Gabriele Svelto2021/03/16 07:23 AM
                      Microkernel?anon22021/03/16 05:13 PM
                        Microkernel?anon22021/03/16 05:16 PM
                    Microkernel?Gian-Carlo Pascutto2021/03/16 01:40 PM
                      Microkernel?anon22021/03/16 05:53 PM
                        Microkernel?Linus Torvalds2021/03/16 07:25 PM
                          Microkernel?Doug S2021/03/17 09:30 AM
                            Microkernel?Linus Torvalds2021/03/17 10:30 AM
                              Microkernel?Brendan2021/03/17 10:56 PM
                                Microkernel?Michael S2021/03/18 03:47 AM
                                  Microkernel?Brendan2021/03/18 09:07 AM
                              Microkernel?Jose2021/03/18 09:35 AM
                            Microkernel?zArchJon2021/03/18 05:42 PM
                          TransputerRichardC2021/03/17 09:47 AM
                          Microkernel?dmcq2021/03/17 11:15 AM
                            Microkernel?Linus Torvalds2021/03/17 11:59 AM
                              Microkernel?dmcq2021/03/17 12:38 PM
                              Microkernel?Adrian2021/03/17 01:00 PM
                              Microkernel?Ana R. Riano2021/03/18 04:33 AM
                              Microkernel?2021/04/30 04:52 PM
                          Microkernel?NvaxPlus2021/03/17 11:48 AM
                            Microkernel?Michael S2021/03/18 03:32 AM
                              Microkernel?Adrian2021/03/18 04:12 AM
                                Microkernel?dmcq2021/03/18 06:30 AM
                                  Microkernel?dmcq2021/03/18 06:55 AM
                                  Microkernel?Adrian2021/03/18 08:35 AM
                                    Microkernel?---2021/03/18 09:49 AM
                                    Microkernel?dmcq2021/03/18 10:59 AM
                                      Microkernel?dmcq2021/03/18 04:09 PM
                              Microkernel?---2021/03/18 09:27 AM
                          Microkernel?Kalle A. Sandström2021/03/20 06:34 AM
                            Microkernel?---2021/03/20 08:35 AM
                            Microkernel?anon22021/03/21 05:29 PM
            Microkernel?dmcq2021/03/15 04:06 AM
              Microkernel?anon22021/03/15 04:59 AM
                Microkernel?dmcq2021/03/15 11:51 AM
                  Microkernel?anon22021/03/15 08:31 PM
                    Microkernel?dmcq2021/03/16 09:17 AM
                      Microkernel?Jukka Larja2021/03/16 11:22 AM
                        Microkernel?dmcq2021/03/16 04:06 PM
                          Microkernel?Jukka Larja2021/03/17 03:42 AM
                            Microkernel?dmcq2021/03/17 07:00 AM
                      Microkernel?anon22021/03/16 05:26 PM
                    Microkernel?---2021/03/16 10:07 AM
            Microkernel?-.-2021/03/15 08:15 PM
              Microkernel?anon22021/03/15 09:18 PM
                Microkernel?Foo_2021/03/16 03:37 AM
                  Read the thread (NT)anon22021/03/16 05:27 PM
                    Already did (NT)Foo_2021/03/17 02:55 AM
                      Already didanon22021/03/17 03:46 AM
                        Already didEtienne Lorrain2021/03/18 02:31 AM
                Microkernel?-.-2021/03/17 05:04 AM
                  Microkernel?Gabriele Svelto2021/03/17 08:53 AM
                    Microkernel?-.-2021/03/17 02:43 PM
              Microkernel?dmcq2021/03/16 08:40 AM
        x86 - why unite when you can fragment?Konrad Schwarz2021/03/17 10:19 AM
    x86 - why unite when you can fragment?anonon2021/03/15 07:37 AM
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