The limits of single CPU speed are here.

By: slacker (, March 17, 2008 10:04 am
Room: Moderated Discussions
Howard Chu ( on 3/17/08 wrote:
>That's a non-sequitur. Nobody said it had to be CMOS-based. E.g. graphene...

You were talking about CMOS whether or not you were aware of it. Let us go back to the statement which spawned this dialogue:

    "Considering all the news articles about terahertz transistors recently,
    it's probably premature to say we've hit a permanent clock speed limit."

The only sort of news you hear about terahertz transistors falls under one of the following four categories:

1. Theoretical models for the f_t or f_max of NMOS devices
2. Theoretical models for the f_t or f_max of GaAs BJTs or InP HBTs
3. Theoretical models for the f_t or f_max of some kind of HEMT or pHEMT
4. A supercooled, one-off version of one of the above

Now, no one cares about GaAs, InP, BJTs, HEMTs, or pHEMTs for any sort of digital logic. This is because all of those circuits consume incredible amounts of static power, which is simply not viable. If it were viable, we'd just use ECL, but we don't. Thus, the only viable THz-transistor technology you could have been talking about are NMOS devices on a CMOS process.

You might be angry at this point and want to scream out, "no one said it has to be CMOS technology!!" Well, the problem here is that there simply isn't any news about THz graphene/ballstic transistors. To the best of my knowledge, there aren't any papers which report f_t or f_max figures for graphene/ballistic transistors. There are papers which report theoretical electron mobility values of 15 000cm^2/(V*s) for graphene, but nothing about actual transistor performance. There are the researchers at Rochester who seem to think they can build single-electron, ballistic transistors, but I haven't seen any results.

I would love to be proven wrong here and shown high-performance carbon transistors, because then I can have more optimism towards alternate transistor materials and structures. I believe that a change of materials/structures is fundamentally necessary towards the continued frequency scaling of large-scale, digital integrated circuits. However, until someone can actually make these devices in more than single-unit quantities, I will remain pessimistic towards the future of digital VLSI.
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TopicPosted ByDate
Multicore is unlikely to be the ideal answer.Anders Jensen2008/02/14 04:24 AM
  And the links..Anders Jensen2008/02/14 04:25 AM
    Disappointing..Linus Torvalds2008/02/14 10:17 AM
      Disappointing..Mark Roulo2008/02/14 11:03 AM
        LOL (NT)Linus Torvalds2008/02/14 05:43 PM
      Disappointing..David Patterson2008/02/15 11:53 AM
        Disappointing..Linus Torvalds2008/02/15 05:01 PM
          Disappointing..anon2008/02/15 08:54 PM
            Disappointing..JasonB2008/02/19 07:45 PM
          Disappointing..Ilya Lipovsky2008/02/22 06:27 PM
          Disappointing..Scott Bolt2008/03/16 11:36 AM
        Need for new programming languagesVincent Diepeveen2008/02/19 06:18 AM
          Need for new programming languagesPete Wilson2008/02/24 11:41 AM
        Disappointing..Zan2008/02/25 10:52 PM
      Disappointing..Robert Myers2008/02/19 09:47 PM
        Disappointing..Fred Bosick2008/02/22 06:38 PM
          Disappointing..Robert Myers2008/03/01 01:17 PM
        The limits of single CPU speed are here.John Nagle2008/03/14 10:55 AM
          The limits of single CPU speed are here.Howard Chu2008/03/15 01:02 AM
            The limits of single CPU speed are here.slacker2008/03/15 08:08 AM
              The limits of single CPU speed are here.Howard Chu2008/03/17 01:47 AM
                The limits of single CPU speed are here.slacker2008/03/17 10:04 AM
    And the links..Howard Chu2008/02/14 12:58 PM
      I take some of that backHoward Chu2008/02/14 01:55 PM
      And the links..Jesper Frimann2008/02/14 02:02 PM
      And the links..Ilya Lipovsky2008/02/15 02:24 PM
        And the links..iz2008/02/17 10:55 AM
          And the links..JasonB2008/02/17 07:09 PM
            And the links..Ilya Lipovsky2008/02/18 01:54 PM
              And the links..JasonB2008/02/18 10:34 PM
                And the links..Thiago Kurovski2008/02/19 07:01 PM
                  And the links..iz2008/02/20 10:36 AM
                And the links..Ilya Lipovsky2008/02/20 03:37 PM
                  And the links..JasonB2008/02/20 06:28 PM
        And the links..JasonB2008/02/17 06:47 PM
          And the links..Ilya Lipovsky2008/02/18 02:27 PM
            And the links..JasonB2008/02/18 10:00 PM
              And the links..JasonB2008/02/19 03:14 AM
              And the links..Ilya Lipovsky2008/02/20 04:29 PM
                And the links..JasonB2008/02/20 06:14 PM
                  And the links..Ilya Lipovsky2008/02/21 11:07 AM
    And the links..Howard Chu2008/02/14 01:16 PM
      And the links..Jukka Larja2008/02/15 03:00 AM
      Berkeley View on ParallelismDavid Kanter2008/02/15 11:41 AM
        Berkeley View on ParallelismHoward Chu2008/02/15 12:49 PM
          Berkeley View on ParallelismDavid Kanter2008/02/15 03:48 PM
            Berkeley View on ParallelismHoward Chu2008/02/17 05:42 PM
              Berkeley View on Parallelismnick2008/02/17 09:15 PM
                Berkeley View on ParallelismHoward Chu2008/02/18 04:23 PM
                  Berkeley View on Parallelismnick2008/02/18 10:03 PM
                    Berkeley View on ParallelismHoward Chu2008/02/19 01:39 AM
                  Berkeley View on Parallelismrcf2008/02/19 12:44 PM
                    Berkeley View on ParallelismHoward Chu2008/02/19 03:25 PM
              Average programmersanon2008/02/18 12:40 PM
        Berkeley View on ParallelismJasonB2008/02/15 08:02 PM
        Berkeley View on ParallelismJasonB2008/02/15 08:02 PM
          Berkeley View on ParallelismDean Kent2008/02/15 08:07 PM
          Berkeley View on ParallelismRay2008/02/20 03:20 PM
            Berkeley View on ParallelismJasonB2008/02/20 06:11 PM
              Berkeley View on ParallelismFritzR2008/02/24 03:08 PM
          rubyinline, etc.nordsieck2008/02/22 03:38 PM
            rubyinline, etc.JasonB2008/02/23 05:53 AM
              rubyinline, etc.nordsieck2008/03/02 01:40 AM
                rubyinline, etc.Michael S2008/03/02 02:49 AM
                  rubyinline, etc.Dean Kent2008/03/02 07:41 AM
                    rubyinline, etc.Michael S2008/03/02 08:19 AM
                      rubyinline, etc.Dean Kent2008/03/02 08:30 AM
                        rubyinline, etc.JasonB2008/03/02 05:26 PM
                rubyinline, etc.JasonB2008/03/02 06:01 PM
                  rubyinline, etc.Anonymous2008/03/03 02:11 AM
                    rubyinline, etc.JasonB2008/03/03 09:40 AM
                      rubyinline, etc.Foo_2008/03/09 09:59 AM
                        rubyinline, etc.JasonB2008/03/10 01:12 AM
                        rubyinline, etc.Gabriele Svelto2008/03/10 02:22 AM
                          rubyinline, etc.JasonB2008/03/10 04:35 AM
                            C++ for beginnersMichael S2008/03/10 05:16 AM
                              C++ for beginnersJasonB2008/03/10 06:35 AM
                          C++Michael S2008/03/10 04:55 AM
                rubyinline, etc.Linus Torvalds2008/03/03 11:35 AM
                  rubyinline, etc.Dean Kent2008/03/03 02:35 PM
                    rubyinline, etc.JasonB2008/03/03 03:57 PM
                      rubyinline, etc.Dean Kent2008/03/03 08:10 PM
                        rubyinline, etc.Michael S2008/03/04 01:53 AM
                          rubyinline, etc.Dean Kent2008/03/04 07:51 AM
                            rubyinline, etc.Michael S2008/03/04 08:29 AM
                              rubyinline, etc.Dean Kent2008/03/04 08:53 AM
                                rubyinline, etc.Michael S2008/03/04 11:20 AM
                                  rubyinline, etc.Dean Kent2008/03/04 02:13 PM
                                    read it. thanks (NT)Michael S2008/03/04 04:31 PM
                  efficient HLL'sPatrik Hägglund2008/03/04 03:34 PM
                    efficient HLL'sWes Felter2008/03/04 09:33 PM
                      efficient HLL'sPatrik Hägglund2008/03/05 01:23 AM
                        efficient HLL'sMichael S2008/03/05 02:45 AM
                          efficient HLL'sWilco2008/03/05 05:34 PM
                            efficient HLL'sHoward Chu2008/03/05 07:11 PM
                              efficient HLL'sWilco2008/03/06 02:27 PM
                    efficient HLL'sanon2008/03/05 08:20 AM
      And the links..Groo2008/02/17 04:28 PM
        And the links..Vincent Diepeveen2008/02/18 02:33 AM
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