395 vs 395x GPU Power Consumption

Discussion in 'iMac' started by Avery1, Jan 12, 2016.

  1. Avery1 macrumors member

    Joined:
    Mar 14, 2010
    #1
    Are there any energy consumption/thermal comparisons of the 395 vs 395x, under light use of the GPU (i.e. not doing any graphics work)?

    Mainly, I am wondering if at idle / with basic machine use (web browsing, mail, documents) if there is a significant power consumption difference between the two. I'm OK having it consume a lot of energy when doing video editing, etc, but would not want a power-hog that is always consuming much more than its counterpart with light computer usage.

    Thanks!
    Avery
     
  2. Samuelsan2001 macrumors 603

    Joined:
    Oct 24, 2013
    #2
    It might use less by getting things done far quicker and returning to an idle state, it really will make no practical difference so don't worry about it.
     
  3. maflynn Moderator

    maflynn

    Staff Member

    Joined:
    May 3, 2009
    Location:
    Boston
    #3
    I think the differences will be small compared to the rest of the power consumption of the computer.
     
  4. Avery1 thread starter macrumors member

    Joined:
    Mar 14, 2010
    #4
    Samuelsan2001 - True, it might be more efficient under heavy load, though what I'm reading is it is going to require a really heavy load to 'need' the added benefit of the 'x' edition. Gaming (which I don't do) and 4k editing (which I plan to do after I have cameras that support it). Most of the time it won't be needed, but as I understand we are also at this cusp of hardware which can work reasonably well editing 4k such as multicam -- and thus those incremental gains can might good for longevity.

    maflynn - Yeah, that's what I'm trying to understand. I don't mind an extra 15 watts running in the background with low usage. I do mind if it's another 50 watts running 24x7... I think of watts at 24x7 being something like $1/watt/yr
     
  5. maflynn Moderator

    maflynn

    Staff Member

    Joined:
    May 3, 2009
    Location:
    Boston
    #5
    Have you worked out the actual cost? I'd be curious to know the details.
     
  6. DaakuMaujii macrumors member

    DaakuMaujii

    Joined:
    Oct 25, 2015
    #6
    Modern computer hardware is very efficient when not being used/idle; so I doubt there will be much of a difference between the 395 and 395x in terms of Watt when not being used. When running at full power you might notice a difference though.

    I had posted some results on power usage in another thread: http://forums.macrumors.com/threads...fer-for-5k-retina-imac.1942412/#post-22326212
    In brief, the 395x runs idle at 25W with screen turned off.

    If you are interested in the cost: power in Watt * number of hours / 1000 * price per 1kWh electricity.
    In my case running the iMac 24/7 idle for a full year would mean 25[W] * 24[hours/day]*365[day/year] / 1000 * 0.23[€/kWh] = €50.37 per year.
    --- Post Merged, Jan 13, 2016 ---
    Oh, i also found some measurements when stressing the CPU in case you are interested. Mine is a core i7, so i tested the power consumption by increments of one thread at full load, up to 9 threads to make sure all cores (both physical and logical) where running at 100%. Below are the results with power consumption, temperature of CPU proximity in ˚C, and fan speed listed:

    1 thread 41W, 30˚C, 1200rpm
    2 thread 64W, 35˚C, 1200rpm
    3 thread 75W, 39˚C, 1200rpm
    4 thread 92W, 43˚C, 1200rpm
    5 thread 107W, 48˚C, 1200rpm
    6 thread 112W, 53˚C, 1800rpm -> fan speeds up right after start of fifth process, eventually settle at 1800rpm
    7 thread 117W, 54˚C, 2100rpm -> again, fan speeds up, eventually settle at 2100rpm
    8 thread 119W, 54˚C, 2300rpm
    9 thread 121W, 54˚C, 2500rpm

    You can clearly see the increase in power for each core that is occupied, until the system saturated the available processing power.
     
  7. DaakuMaujii macrumors member

    DaakuMaujii

    Joined:
    Oct 25, 2015
    #7
    Turns out Cities Skylines is a good GPU test to measure power consumption. According to iStat, the GPU is completely taxed during gaming, while the CPU load is only about 60% of a single core. The power draw during gaming is about 140W, which means the GPU draws about 100W up to maybe 120W when put to the max. Running eight threads in the background during gaming brings the power consumption to max 210W; haven't been able to push it beyond that number.
     
  8. Avery1 thread starter macrumors member

    Joined:
    Mar 14, 2010
    #8
    Yes, albeit a couple years ago. I'm in Colorado. I don't recall the specifics - $.85 or $1.05, but somewhere close enough for me to round it to a buck per watt per year @ 24x7
    --- Post Merged, Jan 13, 2016 ---
    DaakuMaujii - thanks for all the info. Very helpful. Do you have a sense of how much power the machine uses with a few concurrent tasks going on, such as web browsing, writing a document, typing an email, and playing some music? Obviously this will vary quite a bit, but curious how much power is being user. Thanks again for all the info!
     
  9. joema2 macrumors 65816

    joema2

    Joined:
    Sep 3, 2013
    #9
    Your numbers about $1/watt/yr are correct but the 395X does not remotely use an extra 50 watts over the otherwise-identically configured 395 system. My entire 2015 iMac 27 including two external RAID arrays pulls an average of 95 watts and under peak load increases to about 150 watts. The 24x7 average will be closer to the 95 watt figure. For more details on iMac power consumption and electricty cost, see this thread: http://forums.macrumors.com/threads/how-much-it-cost-to-run-an-imac-5k-for-a-year.1945794/
     
  10. Avery1, Jan 13, 2016
    Last edited: Jan 13, 2016

    Avery1 thread starter macrumors member

    Joined:
    Mar 14, 2010
    #10
    I was exaggerating at 50 watts idle, but do know the GPUs have the potential to be one of the most power intensive parts of the machine. Thanks for the info on usage/power. Based on these and other numbers, I'm going to guess it runs an additional 0-15 watts under light usage, by comparison to the 395. Just my gut guess, based on idle versus max versus cpu consumption. Thanks, all!
     
  11. maflynn Moderator

    maflynn

    Staff Member

    Joined:
    May 3, 2009
    Location:
    Boston
    #11
    Thanks for the detailed logic in computing the cost :)

    So for me, fifty bucks a year isn't all that much, not enough to be concerned about it. Think about it, costs 4.16 dollars a month or 13 cents a day.
     
  12. DaakuMaujii macrumors member

    DaakuMaujii

    Joined:
    Oct 25, 2015
    #12
    The hardware in the iMac is very efficient that when it's not being used, components will enter an idle/standby state to save energy. This happens all automatically and very rapidly; e.g. the moment processing power is needed, the cores wake up and start crunching numbers, and when the processing is done they immediately return to their idle/standby state. Simply starting Safari makes it jump up to 80W for a brief second.

    In typical usage like web browsing, listening to music, or download some large file off the Internet: with the screen at half brightness, the power consumption varies between ~40W (hardly doing anything) up to 60W (just going about) with the occasional peaks to ~80W. Watching Netflix HD stream fullscreen in Safari (no UHD unfortunately) consumes ~100W. Downloading updates for Office 2016 @ 5MB/sec uses ~60W, installing the updates about 80W, and when it's done it immediately returns to 35W idle again. At the current price of electricity, I wouldn't worry too much about the power consumption during typical usage, especially not compared to the cost of the iMac itself ;)

    And in case you are worried about your electrical bill, just moving the mouse cursor rapidly around the screen will cost you a little over 1W (not including the calories you burn during the exercise). But seriously; I read a lot of articles on my MacBook Pro, and when trying to make the batteries last as long as possible I use the Page Up and Page Down keys to go through the document because continuous scrolling and updating the screen takes a lot more power than you would expect, especially when vector graphics are included in the document!
     

Share This Page