How much difference does Xeon 130W TDP make in the real world?

Discussion in 'Mac Pro' started by johngwheeler, Jan 1, 2014.

  1. johngwheeler macrumors 6502

    Dec 30, 2010
    I come from a land down-under...
    There's been a fair bit of comparison of Geekbench scores for the nMP against other Macs, particularly for the 4-core nMP which has a similar score to the higher end rMBPs and iMacs.

    Obviously Geekbench doesn't tell the whole story, as it doesn't seem to take memory capacity, GPU etc. into account, nor does it appear to test "long term load".

    One of the advantages of the Xeon would seem to be its much higher TDP when compared to the iMacs and especially the Mac Books. In theory, this should mean that CPU turbo speeds can be maintained for much longer periods.

    Does anyone know how much effect this has in most "real world" applications? Not everyone will be doing multi-hour video exports or running calculations for days on end, where obviously sustained CPU speed becomes very significant.

    In other words, how quickly do iMac & rMBP CPUs find themselves throttled, and would the nMP suffer significantly less from this?

    I would like to have seen AnandTech run comparison of the 4-core nMP against the other Macs, rather than the fully-loaded 12-core version, which is going to appeal to small minority. Maybe someone else is working on this?

  2. PmattF macrumors member

    Dec 28, 2006
    This application from Intel is handy for watching to see if your CPU is throttling down...

    I just used Lightroom to generate 350 full size previews of 36 megapixel Nikon D800 raw images, which runs at about 350% of CPU for quite a while (didn't time it), and the CPU speed did not drop. I have a feeling that it could do that all day.

    I am curious too what would actually make it throttle. Maybe a long running handbrake job?
  3. paulrbeers macrumors 68040

    Dec 17, 2009
    There isn't a lot of difference. The high end iMac i7 processor is as fast if not faster than the 4 core Mac Pro. If your work flow does not require GPUs and quad core processing is more than enough them go with the iMac. The whole point if this machine IS for those who do a lot of rendering accelerated by the GPU or need a LOT of CPU grunt. If you you only occasionally need one or the other than save yourself some cash and stick to the iMac.
  4. propower, Jan 1, 2014
    Last edited: Jan 1, 2014

    propower macrumors 6502a

    Jul 23, 2010
    I tested the Late 2013 imac i5 3.4GHz and i7 3.5GHz configurations for thermal performance under load. The i7 will run a constant 70% total CPU load without hitting 90degC. That means - no extra fan noise - no throttling from Turbo (3.7GHz). Somewhere between 70 and 80% the fan will come on and keep the CPU ~95degC. I did not test for throttling at that time but I would suspect it takes closer to 100degC to 105degC before that starts. Regardless - to 70% constant CPU load no issue.

    The 3.4GHz i5 I tested could do 100% constant load and just barely get to 90degC CPU. The fan may or may not even come on.

    WRT CPU loading there will be very little difference to power users between the Quad nMP and the 27" imacs. Any serious GPU loading then the nMP will be significantly faster - more powerful. The nMP by virtue of much larger CPU die size, TDP, and way better heat sinking will do equivalent heavy lifting with much less temp rise and consequent fan noise than an imac -- but only after a constant heavy load -- till then - not much different.

    One does not buy speed anymore - they buy, form factor, parallel processing power, GPU power and noise performance under heavy loads.

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