Definitions of RISC (nod to John Mashey and comp.arch)

By: wumpus (lost.delete@this.in.a.cave), February 21, 2019 5:29 pm
Room: Moderated Discussions
Adrian (a.delete@this.acm.org) on February 21, 2019 1:42 pm wrote:
> Brendan (btrotter.delete@this.gmail.com) on February 21, 2019 9:07 am wrote:
> >
> > My definition of RISC is that there's a reduced number of instructions (not a buttload
John Mashey had a long-winded explanation that he regularly posted on comp.arch, here's a link to one from 1995: https://www.yarchive.net/comp/risc_definition.html

From other posts, I think addressing modes was the most critical, but ARM breaks the RISC rules in a few other places.
3a: Thumb allows two different sizes of instruction length
3b: the main one (for thumb) is 16bit
6a: they have less than 32 integer registers
6b: architectural definition of floating point (and thus number of fp registers) is often implementation specific...

I'm not familiar enough with ARM to know the rest off the top of my head, but further down the post ARM's addressing modes are in a chart and they appear to fall in the no-man's-land between RISC and CISC (ARM doesn't have indirect addressing, but does require some complicated addressing that shouldn't require an additional memory access).

I will admit that this list doesn't appear to check for special purpose registers, something of a CISC hallmark and shunned by RISC, and feels related to the complaints against this new ARM architecture.

I think the real rule for a RISC architecture is "anything designed after the mid/late 1980s", with a possible "post-RISC" title claimed by anyone with enough ambition to break free of RISC's rules (so far, no post-RISC architecture has succeeded for general purpose computing).
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ARM announces Aresnobody in particular2019/02/20 07:35 AM
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                          ARM announces AresJS2019/02/20 11:59 PM
                            *has not hasn't (NT)JS2019/02/21 12:01 AM
                            ARM announces AresSalvatore De Dominicis2019/02/21 06:05 AM
                        Definitions of RISCBrendan2019/02/21 09:07 AM
                          Definitions of RISCMichael S2019/02/21 09:16 AM
                          PDP-8 Not Usually Considered RISCMark Roulo2019/02/21 01:10 PM
                            PDP-8 Not Usually Considered RISCrwessel2019/02/21 06:13 PM
                          Definitions of RISCAdrian2019/02/21 01:42 PM
                            Definitions of RISC (nod to John Mashey and comp.arch)wumpus2019/02/21 05:29 PM
                              Definitions of RISC (nod to John Mashey and comp.arch)none2019/02/21 11:32 PM
                                Definitions of RISC (nod to John Mashey and comp.arch)Michael S2019/02/22 03:28 AM
                                  Definitions of RISC (nod to John Mashey and comp.arch)none2019/02/22 07:01 AM
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    stability? (NT)anonymous22019/02/20 09:01 AM
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        That last line should have been removed :-) (NT)none2019/02/20 11:04 PM
        ARM announces AresMichael S2019/02/21 12:47 AM
          ARM announces Aresnone2019/02/21 02:59 AM
            ARM announces AresMichael S2019/02/21 03:45 AM
            ARM announces Aresdmcq2019/02/21 04:18 AM
              ARM announces AresSimon Farnsworth2019/02/22 08:43 AM
    ARM announces Aresanon2019/02/20 08:27 PM
      ARM announces AresMichael S2019/02/21 12:53 AM
        ARM announces AresLinus Torvalds2019/02/21 08:03 AM
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                    In other words: nobody will ever get fired for choosing x86 (NT)Gabriele Svelto2019/02/24 12:32 PM
                      In other words: nobody will ever get fired for choosing x86Simon Farnsworth2019/02/25 03:53 AM
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                    ARM announces AresMaynard Handley2019/02/25 11:32 PM
                      ARM announces AresGabriele Svelto2019/02/26 11:14 AM
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            ARM announces Aresanon2019/02/21 07:19 PM
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          software ecosystemsRichardC2019/02/21 03:31 PM
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              + on hyperscalingMaynard Handley2019/02/22 07:38 AM
                + on hyperscalingjuanrga2019/02/22 10:57 AM
            + on hyperscalingdmcq2019/02/22 07:23 AM
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                        why not?Michael S2019/02/25 09:43 AM
                          why not?dmcq2019/02/25 10:35 AM
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                              why not?Not the parent2019/02/26 09:08 AM
                                why not?Doug S2019/02/26 11:05 AM
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                                              why not?dmcq2019/02/27 05:19 PM
                                                why not?anon2019/02/27 05:46 PM
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                                                    why not?Jukka Larja2019/02/28 06:02 AM
                                                      why not?Michael S2019/02/28 07:32 AM
                                                      why not?Wilco2019/02/28 08:40 AM
                                                      why not?Doug S2019/02/28 09:13 AM
                                                        why not?Foo_2019/03/01 06:35 AM
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                                                              why not?dmcq2019/03/01 02:13 PM
                                                                why not?anon2019/03/01 03:13 PM
                                                                  why not?dmcq2019/03/02 02:56 AM
                                                                    why not?anon2019/03/02 09:09 AM
                                                                      why not?dmcq2019/03/02 09:41 AM
                                                                        why not?anon2019/03/02 11:19 AM
                                                                          why not?dmcq2019/03/03 02:48 AM
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                                                                                why not?dmcq2019/03/03 05:33 AM
                                                                                  I considired dry humor a Brittish specialty. It seems, I was wrong about it. (NT)Michael S2019/03/03 05:39 AM
                                                                                  why not?anon2019/03/03 09:13 AM
                                                                                    why not?Michael S2019/03/03 11:41 AM
                                                                                      why not?dmcq2019/03/03 12:21 PM
                                                                                        why not?anon2019/03/03 03:15 PM
                                                    why not?anon2019/02/28 07:38 PM
                                              why not?Not the parent2019/02/28 12:48 AM
                                                strawman (NT)anon2019/02/28 07:31 PM
                            why not?Michael S2019/02/27 02:53 AM
                              why not?Not the parent2019/02/27 04:26 AM
                                why not?Michael S2019/02/27 04:42 AM
                              why not?dmcq2019/02/27 04:49 AM
                                why not?Michael S2019/02/27 05:21 AM
                                  why not?dmcq2019/02/27 06:15 AM
                                Selling at multiple layersPaul A. Clayton2019/02/27 10:25 AM
                                  Selling at multiple layersDoug S2019/02/27 11:45 AM
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                                      Selling at multiple layersDoug S2019/02/27 03:04 PM
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                                          Arm reference board?Simon Farnsworth2019/02/28 11:34 AM
                                why not?Doug S2019/02/27 11:46 AM
                      why not? (NT)la mama de murgay2019/02/25 09:22 PM
                    Chicken or egg, both.Ronald Maas2019/02/25 12:23 PM
            ARM announces AresGabriele Svelto2019/02/24 02:07 PM
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              TrollDoug S2019/02/23 12:37 AM
                TrollDavid Soul2019/02/23 07:59 AM
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                ARM announces AresFoo_2019/02/23 01:38 AM
                  ARM announces Aresanon2019/02/23 02:46 AM
                ARM announces Aresdmcq2019/02/23 04:41 AM
  ARM announces Aresnobody in particular2019/02/26 02:58 AM
    expensiveanonymous22019/02/26 11:46 PM
    ARM announces AresHoward Chu2019/02/27 06:19 AM
      ARM announces AresHoward Chu2019/02/27 06:21 AM
        ARM announces Aresdmcq2019/02/27 06:57 AM
        ARM announces AresJukka Larja2019/02/27 07:11 AM
          ARM announces AresMichael S2019/02/27 07:16 AM
            ARM announces AresDoug S2019/02/27 11:49 AM
              ARM announces AresMichael S2019/02/27 12:43 PM
                ARM announces AresDoug S2019/02/27 03:06 PM
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                ARM announces AresGian-Carlo Pascutto2019/02/28 04:02 AM
                  ARM announces AresMichael S2019/03/01 02:47 AM
                    death by a thousand cutsMichael S2019/03/01 06:27 AM
                      death by a thousand cutsFoo_2019/03/01 06:37 AM
                        death by a thousand cutsdmcq2019/03/01 11:10 AM
              ARM announces AresJukka Larja2019/02/28 05:31 AM
                ARM announces AresHoward Chu2019/02/28 08:17 AM
                  ARM announces AresGabriele Svelto2019/02/28 02:02 PM
                    ARM announces Aresaaron spink2019/03/01 12:19 AM
                ARM announces AresAndrew Clough2019/02/28 10:32 AM
                  ARM announces AresAndrew Clough2019/02/28 10:33 AM
                  ARM announces AresFoo_2019/03/01 12:55 AM
                  ARM announces AresJukka Larja2019/03/01 04:40 AM
          ARM announces AresHoward Chu2019/02/27 07:45 AM
            ARM announces Aresdmcq2019/02/27 08:17 AM
              ARM announces Aresdmcq2019/02/27 08:21 AM
                ARM announces AresHoward Chu2019/02/27 03:03 PM
            ARM announces AresJukka Larja2019/02/28 05:03 AM
      ARM announces Aresnone2019/02/27 10:49 PM
        ARM announces AresHoward Chu2019/02/28 03:26 AM
          ARM announces AresPeter E. Fry2019/02/28 06:31 PM
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            ARM announces AresGabriele Svelto2019/03/01 11:56 PM
              ARM announces AresHoward Chu2019/03/02 09:05 AM
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