Are the new iMacs PWM Free?

Discussion in 'iMac' started by aman74, Nov 16, 2015.

  1. aman74 macrumors newbie

    Aug 9, 2011
    Google didn't help me on this one...

    Wondering if the new lineup is PWM free? I see on the iFixit teardown for the 27" that it has listed a PWM controller, but I'm not positive that means it uses PWM and will have the issue.

    I am curious about the entire line, but mostly about the 27".

    Also, I'm sure there's been a lot of discussion, but if anyone could give me the quick and dirty on whether or not any GPU upgrade on the 27" is worthwhile?

  2. m85476585 macrumors 65816

    Feb 26, 2008
    What's wrong with PWM? Are you allergic to it? iMacs are gluten free, nut free, dairy free, etc. but not PWM free.

    There is probably PWM control for the fans, the display brightness, and there is probably even a variant of it for the audio output (filtered, of course). Basically anything analog is probably going to be driven by PWM because that's one of the best ways for a digital device to make analog signals.

    It probably doesn't have any issues, or you would read about them here.
  3. G.McGilli macrumors regular

    Oct 19, 2015
    I can vouch for this.
  4. AppleHater macrumors 6502a

    Jun 9, 2010
    It's also fat free and cholesterol free, but unfortunately has little nutritional value, either, other than some iron and minerals.
  5. makrom, Nov 18, 2015
    Last edited: Nov 18, 2015

    makrom macrumors regular

    Nov 4, 2015
    A very rough rule of thumbs:
    M395X: 100%
    M395: 90%
    M390: 80%
    M380: 40%

    So if you care about GPU acceleration, don't get the M380. The advantage of the M395X will be a lot bigger for use cases that benefit a lot from extra VRAM. There are other threads around here that handle this topic much more in depth.
  6. aman74 thread starter macrumors newbie

    Aug 9, 2011
    I'm referring to the display and there are many health and comfort concerns over the use of PWM displays. This is why there are lists dedicated to which monitors are free of it on tftcentral. Most Apple products have been PWM free so it would be disappointing to hear that this has changed.
  7. makrom macrumors regular

    Nov 4, 2015
    Yes I agree. I am majorly annoyed by some PWM screens or 60Hz CRTs. I didn't notice such an effect with the retina iMacs, but I can't say for sure whether they don't use PWM panels.
    I also don't notice it when TVs are using black frame inserts or backlight strobing at frequencies above 200Hz. If you do notice that, you shouldn't take my word for it.
  8. m85476585 macrumors 65816

    Feb 26, 2008
    Thanks, I was not aware of flicker free monitors. Sorry about my sarcastic reply earlier.

    The flicker free database on TFTCentral goes kind of over the top, not allowing monitors with even very high switching frequencies. Images persist long enough in our vision that high frequency switching (probably over a few hundred hertz) is invisible. With appropriate filtering or a high enough frequency, PWM is not a problem

    Maybe a simple test would work. Wave your hand in front of the monitor. If you see a strobing effect, it might have some noticeable flickering. My monitor at work fails this test, but my Macbook pro passes the test. I don't have a new iMac, but it would be easy to try in the store.

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