Why do the low GHz M chips perform so well?

Discussion in 'MacBook' started by Mike Boreham, May 11, 2018.

  1. Mike Boreham macrumors 65816

    Joined:
    Aug 10, 2006
    Location:
    UK
    #1
    I believe one of the reasons the 12" MacBooks tend to be underestimated by people who haven't used or investigated them is the very low spec CPU GHz numbers, in the range 1.1 to 1.4 GHz.

    I never lose an opportunity to extoll the MacBooks when I see people underestimating its capability, but I realise I don't have a proper explanation.

    My understanding is that it is all in the turbo boost which is a much bigger multiple of the base speed in the M series, eg 1.2 turbo to 3.0 in the MacBook, compared to 3.1 up to 3.5 in the 13" MBP.

    Since turboboost seems to be so effective in the fanless 12" MacBook, why isn't more turbo used in the cooled MBP. As we know throttling due to temperature is not nearly as big a factor in the MacBook as commonly thought so similar should apply, to some degree in the MBPs.

    I'm sure there are very good reasons....I am just trying to increase my understanding.
     
  2. Darmok N Jalad macrumors 65816

    Darmok N Jalad

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    Sep 26, 2017
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    Tanagra
    #2
    “Turbo” mode as it appears in most modern CPU and GPUs today is very dependent on workload. Often times the processor boosts for a limited amount of time before thermal limits are reached. This is why you get the much lower advertised speed, as the advertised speed is the guaranteed sustained clock under heavy workloads. In brief tasks, the processor can boost high, get work done, and then drop down to idle.

    What you see on Core M in MacBook is not anything special compared to the Core i in the MBP. What you are seeing in both cases is the architectural limits of the CPU design. That is, the MBP can’t boost that much higher because those CPUs won’t be stable because of physical design limits, not thermal limits. In other words, both CPUs are able to boost to roughly the same top speeds, but their base sustained clocks are where the difference is found and where the extra cooling becomes effective.
     
  3. Macalway macrumors 68030

    Joined:
    Aug 7, 2013
    #3
    Yeah right. In cooled units it's constantly turbo-ing, but it can stay tacked into the red much longer if not indefinitely. Then if it does get too warm it drops down to a much higher level.

    The fanless models overheat much quicker and drop down to 1 to 4ghz, which is freaking slow. The MacBooks are terrible for intensive work, but for casual stuff and certain things they are perfect.

    For most people they are fine. But for instance, I tried mine (1.3ghz) with a DAW + plugins, and it just didn't even work without distortion at the low latencies. Very telling stuff. I actually thought it would be ok. (not user error here). Totally undoable for what I wanted. Fortunately I have plenty of other machines that can do this stuff.
     
  4. Mike Boreham thread starter macrumors 65816

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    Aug 10, 2006
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    UK
    #4
    I certainly wouldn't claim the MacBooks are suitable for intensive work, but wonder if you have seen this thread:

    https://forums.macrumors.com/thread...uns-of-cinebench.2073415/page-2#post-25271927

    Performance throttling was less than 10% after sustained Cinebench testing.

    How does what you are doing relate to continuous Cinebench loading?
     
  5. SpitUK macrumors 6502

    SpitUK

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    Mar 5, 2010
    Location:
    East Yorkshire, UK
    #5
    Also on the original keynote Apple said that the 12” MacBook ran a special version of MacOS that was designed for speed on these chips.
     
  6. BeatCrazy macrumors 68000

    Joined:
    Jul 20, 2011
    #6
    Interesting. Have a link/timestamp?

    I realize this might sound ridiculous, but if my 12" MacBook starts feeling really hot on the bottom (and I'm worried it will impact workflow), I pull a Pelican frozen cooler "brick" out of the freezer, through it under a towel, and set the rMB on top. Just takes a few minutes to cool down.
     
  7. Mike Boreham thread starter macrumors 65816

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    Aug 10, 2006
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    UK
    #7
    I have not heard that before and my MacBook always had the same build numbers as my other macs.
     

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