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Measuring Power Consumption

Meet The 2012 Graphics Charts: How We're Testing This Year
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Measuring Power Draw

We were faced with the decision whether to measure the power draw of the entire test rig or just the individual cards. As measuring the entire rig isn't very transparent and doesn't yield comparable results, we chose to do it the hard way and measure the power dissipation of individual cards.

After conducting a lengthy series of measurements and test setups, we measured the power draw of our test rig without a graphics card at full CPU load. In order to minimize variance, we don’t use mechanical hard drives anymore, even though a disk-induced error would only be in the 2 or 3 W range. The PC is booted with a decades-old PCI graphics card, and the CPU maxed out with Prime95. Using this setup, we were able to determine a "baseline" draw of the system as 135 W.

In order to measure the power draw of our test cards as precisely as possible, we keep the PCI-based VGA card in the system, in addition to the card being tested, and subject the CPU to a Prime95 load at low priority while performing the actual test. This way, any remaining CPU capacity is consumed by Prime95 without influencing the actual benchmark. The baseline value is then subtracted from the system power draw of the current benchmark. The picture above shows that this works quite well. With a Radeon HD 7970 at idle, the system draws 150 W. Subtracting 135 W from that yields an idle power draw of a mere 15 W for the Radeon 7970, which matches the manufacturer’s spec.

One issue that needs to be discussed has to do with the power supply. The efficiency of a power supply isn't constant, but it changes with the load that the power supply delivers. If we measure the baseline power draw above at a certain PSU load, increasing the load during a benchmark will change the PSU's efficiency and cause the baseline load to be higher; the same setup as before now results in more power draw (due to the lower overall efficiency).

When we compared the power draw that we measured on the (secondary) DC side with the difference between the actual (primary) AC side wattage and the baseline wattage of 135 W, we got quite similar values. Determining the efficiency curve of the power supply and adding that to the equation, we can further refine this measurement and cross-check the accuracy of the clamp meter used for these tests. After tabulating all these measurements, the maximum deviation we ever observed was 5 W at a total system power draw of 435 W and, thus, a graphics card-only power draw of 300 W. As this is a deviation of less than two percent, we consider our method of measuring power draw accurate enough.

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  • 21 Hide
    quixoticism , April 3, 2012 6:46 AM
    I would have preferred to see all the benchmarks at 1920x1080 done with maxed out graphics settings.
    I want to see how the base performance is in games with full detail, and save the heavy AA and resolutions for extreme.
  • 19 Hide
    randomkid , April 3, 2012 5:51 AM
    Where's the 5760x1080? In the area where I come from, 3x 1920x1080p 22" monitor cost around the same or even less than a single 2560x1440/1600 27" monitor so this is a more likely configuration among gamers.

    The 5760x1080 resolution will also push the GPU's harder than a 2560x1440/1600 could so why limit the resolution there?
  • 19 Hide
    johnny_utah , April 3, 2012 4:47 AM
    While I love the new techniques, using BITCOIN to bench GPUGPU performance instead of Folding @ Home? Um, okay.
Other Comments
  • 19 Hide
    johnny_utah , April 3, 2012 4:47 AM
    While I love the new techniques, using BITCOIN to bench GPUGPU performance instead of Folding @ Home? Um, okay.
  • 15 Hide
    Anonymous , April 3, 2012 4:49 AM
    Still with the bar charts? Would *love* to see scatter plots with price/score on the axes... So much more useful in picking out a card.
  • 3 Hide
    AznCracker , April 3, 2012 5:10 AM
    Man the charts are dying to be updated. Too bad it isn't done more often since it takes a lot of work.
  • 5 Hide
    Anonymous , April 3, 2012 5:12 AM
    You havent added how many cheese wheels it can run in skyrim as a benchmark... wth?
  • 9 Hide
    DjEaZy , April 3, 2012 5:14 AM
    ... i like the pile of card's @ the end of the article.... a beautiful pile...
  • 14 Hide
    pharoahhalfdead , April 3, 2012 5:32 AM
    johnny_utahWhile I love the new techniques, using BITCOIN to bench GPUGPU performance instead of Folding @ Home? Um, okay.


    I agree. I know Tom's spends a lot of time benchmarking, but Folding@home is something that is a bit more common. I would love to see F@H in some articles.

    BTW, I appreciate all the work you guys do.
  • 19 Hide
    randomkid , April 3, 2012 5:51 AM
    Where's the 5760x1080? In the area where I come from, 3x 1920x1080p 22" monitor cost around the same or even less than a single 2560x1440/1600 27" monitor so this is a more likely configuration among gamers.

    The 5760x1080 resolution will also push the GPU's harder than a 2560x1440/1600 could so why limit the resolution there?
  • 9 Hide
    Anonymous , April 3, 2012 5:56 AM
    Quote:
    We'll add up to 20 new boards each month until the lower end of the performance range is filled out, too.

    How far back in GPU generations are you going to test, if at all? I saw the power consumption charts and could only see GTX 500, 600 and Radeon 6000, 7000 series. I have an EVGA GTX 480 SC for two years and do like to know how it compares to the newer series of GPUs. Much appreciated.
  • 8 Hide
    Yargnit , April 3, 2012 5:58 AM
    MMO FanYup no surprise here typical Nvidia benchmark suite fuck sakes.


    So what would YOU like to see used then? If they were trying to push Nvidia wouldn't Hawx 2 be in the suite?
  • 16 Hide
    shinym , April 3, 2012 6:18 AM
    For Starcraft II you say "This game doesn't stress the CPU, and is thus well-suited for GPU benchmarking." Looks like you got CPU and GPU mixed up there.
  • 5 Hide
    cangelini , April 3, 2012 6:28 AM
    shinymFor Starcraft II you say "This game doesn't stress the CPU, and is thus well-suited for GPU benchmarking." Looks like you got CPU and GPU mixed up there.

    More than likely, it's the sequence the German team picked that is less CPU-bound than other StarCraft II tests we've used.
  • 10 Hide
    CaedenV , April 3, 2012 6:31 AM
    CommieIBankerStill with the bar charts? Would *love* to see scatter plots with price/score on the axes... So much more useful in picking out a card.

    I would love something like this as well, but as Tom's has a world wide market and the prices vary so greatly from place to place such charts become impractical.

    What I miss about the old charts is that you could easily compare old GPUs to new ones. When upgrading I think people like to have a reference of what they currently have compared to what they are looking at getting. To throw in a few old cards like the 8600GT, 8/9800GT in the mix may help people feel more secure in their purchases, and have a better feel for what they are getting because they can relate the new card to their old one. Not saying Tom's needs to put in every single card from every generation, but a card or 2 from each generation from the last 6 years or so would be nice.

    Another thing I would like is something like Anandtech's bench where when you select your cards you get bar graphs instead of raw numbers in a chart. It is just easier to visually see a 1/3rd difference in performance on a line graph rather than in raw numbers.
  • 21 Hide
    quixoticism , April 3, 2012 6:46 AM
    I would have preferred to see all the benchmarks at 1920x1080 done with maxed out graphics settings.
    I want to see how the base performance is in games with full detail, and save the heavy AA and resolutions for extreme.
  • 0 Hide
    CaedenV , April 3, 2012 6:47 AM
    while speaking of comparison chart complaints:
    -Some cards (though not all) show up as their name, others have a picture of the card with a sales link, and others give very little information at all. It would be nice to make this consistent so that at the top of each column we could see the pic (if available), the name of the card, and then a sales link (hey, you have to pay of the site somehow)

    -organize the comparison charts a little. On the comparison page it just throws all the charts together with no apparent rhyme or reason. It would be nice to have groupings such as physical considerations (temps, noise, and power usage), gpgpu benchmarks, and game benchmarks sorted either by game.

    -Could we add physical dimensions? It would be helpful to some to know how long a card is, and now many slots it takes.

    -lastly, under "02 - Unigine Heaven DirectX 11 Performance 1920x1080, 4xAA, AFx16 Shaders medium Tessellation normal" the "score in" has a blank spot to enter in text (pretty sure it should say 'FPS' here) followed by a broken "Go" link.

    None of these changes should be all that hard to make, and would make the charts much simpler to use when comparing specific cards.
  • 2 Hide
    Anonymous , April 3, 2012 6:53 AM
    Glad to see Bitcoin Mining being included now.
  • 14 Hide
    kyuuketsuki , April 3, 2012 8:50 AM
    quixoticismI would have preferred to see all the benchmarks at 1920x1080 done with maxed out graphics settings.I want to see how the base performance is in games with full detail, and save the heavy AA and resolutions for extreme.

    This. I, along with probably a large chunk of your readers, are probably more interested in performance at maxed out settings at 1080p than skipping from mid-range settings at 1080p to maxed out settings at higher resolutions.
  • 1 Hide
    Anonymous , April 3, 2012 9:10 AM
    Thanks for your work Guys,reading trough since long time and each rig has been built based upon your tests!
    Gabriel
  • 2 Hide
    devBunny , April 3, 2012 12:15 PM
    "What would you rather listen to, a low hum or a high-pitched whine at the same loudness?"

    Lol. Good question. My tinnitus gives me a couple of the lows and several highs (but, just for fun and to keep me noticing them, the pitch and loudness vary). To be honest, I'd rather not hear any of them! ;O)
  • -1 Hide
    devBunny , April 3, 2012 12:33 PM
    Dear Tom's

    Regarding charts, I think it's way past time that you provided dynamic, configurable graphs generated from the data rather than static images. Images are fine if that's all that the web savvy that a site has. Surely Tom's is better than that?! [tease, tease] ;o)

    I'd like graphs that have options, including choice of colours (I sometimes can't easily see the difference between the colours that you use) and scale (so that I don't have to opening images in another tab and manually enlarging them to read the finer details).

    Someone above mentioned scatter diagrams. And why not, if that would suit him? A page that downloads the data rather than an image has scope for creating whatever kind of graph can help represent the data meaningfully.

    Tom's, I invite you to kill me with kindness. ;-)

    ps. By "dynamic", I don't mean animated. That's pointless, even annoying, eye candy. It's only necessary to show the data more clearly, in a form that people prefer.
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