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Connecting The Dots With Web Browsing Power Use

ARM Vs. x86: The Secret Behind Intel Atom's Efficiency
By , Chris Angelini
Microsoft Surface

Load Time (ms)
Platform (W)
CPU (W)
GPU (W)
Memory (W)
Panel Backlight (W)
Everything Else (W)
Standard Page (MSN Homepage)
9413.390.090.270.351.081.60
Standard Page + Split Screen
13984.430.540.540.451.121.79
Complex Page (Long Article on Wikipedia)
17703.460.100.270.321.111.63
Complex Page + Split Screen
20164.240.360.430.511.101.83
Acer W510

Load Time (ms)
Platform (W)
CPU (W)
GPU (W)
Memory (W)
Panel Backlight (W)
Everything Else (W)
Standard Page (MSN Homepage)5802.940.070.120.311.181.26
Standard Page + Split Screen7763.280.180.150.341.171.43
Complex Page (Long Article on Wikipedia)12593.090.120.120.311.121.42
Complex Page + Split Screen14073.370.220.150.351.141.51


First things first. Although these uber-granular numbers were generated in Intel's lab, we can at least confirm that, using Chrome, Safari, or IE10 on Samsung's ATIV Smart PC 500T, the performance of Atom on Windows 8 is greatly superior to Tegra 3 on Windows RT. We haven't published our review on Samsung's Atom-powered tablet yet, but check out the following chart:

Now, with that in mind, the Atom-based Acer also delivers better power performance. Moreover, it's clear that the complexity of a page being displayed affects consumption, Intel's Atom demonstrating its strengths in the GPU and memory categories as Nvidia's ARM-based cores use slightly less power on the more complex webpage. 

This difference can also be seen in the raw results from the test equipment.

Google's homepage: Note the lack of activityGoogle's homepage: Note the lack of activity

MSN's homepage is a lot busier.MSN's homepage is a lot busier.

The first screen shot shows the power consumption of Google’s home page and the second illustrates the power consumption of msn.com. Seeing these graphs and their corresponding power levels should make it clear how difficult it is to assign just one number to a tablet's power use when the actual draw fluctuates pretty wildly. In the actual split-second that the screen shot of MSN's home page was captured, Acer's W510 happened to be using 2.56 W and the Surface was using 4.29 W. The average of both gets calculated to be 2.94 W and 3.39 W (which is how we're reporting it in the table).

It's really interesting that these results come close to matching each manufacturer's advertised specifications. Acer says its W510 will do 9 hours of battery life. If you average the 2.94 W and 3.28 W of power consumption for the first two test cases (3.11 W), you get 8.6 hours. Microsoft says its Surface will do 8 hours of battery life. And if you average the first two rows of the Windows RT-based tablet, you get an average of 3.91 W; a 31.5 Wh battery should deliver 8 hours.

Now, in our own calibrated 200-nit test (which adds MP3 playback in the background), the Surface achieves an 8:03 run time. Asus' Transformer Prime pulls off 8:01 (the same as the Surface), but with a 25 Wh battery instead of the Surface’s 31.5 Wh power source. So, the Transformer Prime’s consumption is probably around 3.12 W. As we saw on the previous page, compared to the Surface, we suspect the Transformer Prime is thriftier with power than Microsoft's tablet, which we'd again be inclined to attribute to Android versus Windows RT and each platform's display.

Time-Out For Some Speculation

Now, let’s speculate a little bit. Intel's decision to use a somewhat-complex webpage in full- and split-screen modes seems to match the way tablet vendors are rating battery life. Call it an unofficial "we don't want to get sued for false advertising" standard.

Andrew’s own numbers generated during our Surface testing (specifically, light Web browsing with Wi-Fi enabled and an MP3 playing back at 200 nits) suggest we'll see 8 hours 3 minutes of run time. In other words, our workload comes pretty close to what vendors seem to be using to test internally. Our test is probably a little more taxing, since we get 9 hours from our iPads instead of the advertised 10, 10 hours from a Kindle Fire HD instead of the advertised 11, and 9 hours from the Nexus 7 instead of the advertised 10.

On the iPad 2, we get 9.08 hours from a 25 Wh battery (solving for W gives us 2.75 W). For the third-gen iPad, 9.25 hours from a 42.5 Wh battery translates to 4.59 W of average power consumption. From this, we learn that the iPad 2 offered superb efficiency that wasn't matched by Apple's successor. We haven't run these numbers on the fourth-gen iPad yet, but power consumption should be similar as the iPad 4 also has a 42.5 Wh battery rated for 10 hours of mixed use.

Testing the power consumption of MSN's home page.Testing the power consumption of MSN's home page.

Google claims claims 7 hours of Web browsing on its Nexus 10 from a 33.75 Wh battery (so, 4.82 W for a 4 MP display) and Samsung's Series 3 XE303C12 Chromebook claims 6.5 hours from a 30 Wh battery (4.62 W for a 13x7 display). If this means paying an extra 0.20 W for a 4 MP display, and we go back to our previous page speculating that 3.75 W is what the Nexus 10 consumes during video playback, then the Chromebook probably will need 3.55 W for video playback running on a standard-resolution display. This also shows us that the fourth-gen iPad with the Swift-powered A6X is more efficient than A15, per our back-of-the-envelope calculations.

I’m willing to bet that the Cortex-A15, in low-power applications like video, is on par with the Atom. But in higher-power applications (ironically, Web browsing), it'll require 50% or so more power than the Atom. We know this must be true to some degree, since Google actually tells us in its advertising that you get less battery life from browsing than watching video. These numbers also suggest that Cortex-A9 is more efficient than -A15 under certain conditions, which is to say that even though -A15 improves performance, we need to see how much real-world work is done within a set thermal threshold.

Just so that Qualcomm doesn’t feel left out, we can probably speculate about its Snapdragon S4, since we know it is being advertised with a vague "up to 10 hours" of run time with a 28 Wh battery on Dell's XPS 10. That’s a best-case 3.11 W, which is what Acer's W510 requires when we average those first two Intel workload numbers.

At the end of the day, Intel's numbers make sense. It's pretty clear that the Atom is on par with today's top SoCs. At least under Windows 8, it's able to turn in better efficiency results than Tegra 3 under Windows RT, and should come close to Tegra 3 under Android, in light of our Transformer Prime numbers. 

When it comes to Web browsing, our best predictions are:

  1. Atom is neck and neck with the power consumption of Qualcomm’s Krait architecture in the Snapdragon S4.
  2. Atom beats Cortex-A15 on power consumption.
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Top Comments
  • 17 Hide
    Novuake , December 24, 2012 8:06 PM
    Excellent! Was wondering about this for some time. Also made the mistake of thinking Intel was behind in the mobile space... Well done Toms.
  • 16 Hide
    tomfreak , December 24, 2012 9:47 PM
    of all the ARM types, u took one of the weakest one? I like to see the numbers vs Qualcomm krait and Apple's A6
  • 14 Hide
    AlanDang , December 24, 2012 8:59 PM
    And the Chromebook with an A15. We're looking at several other SoC's but what's empowering is how simple math can help you look at efficiency.

    But it's Christmas Eve, and sometimes there are more important things than running benchmarks and soldering wires to SoCs. ;) 
Other Comments
  • 17 Hide
    Novuake , December 24, 2012 8:06 PM
    Excellent! Was wondering about this for some time. Also made the mistake of thinking Intel was behind in the mobile space... Well done Toms.
  • 3 Hide
    tipoo , December 24, 2012 8:33 PM
    I'll be very interested to read the Cortex A15 follow up. From what I gather, if compared on the same lithography the A15 core is much larger than the A9, which likely means more power, all else being equal. It brings performance up to and sometimes over the prior generation Atom, but I wonder what power requirement sacrifices were made, if any.

    I'm thinking in the coming years, Intel vs ARM will become a more interesting battle than Intel vs AMD.
  • 3 Hide
    AlanDang , December 24, 2012 8:42 PM
    @tipoo, we're not going to hang our hat on it just yet (until we run the numbers ourselves), but A15 runs hot, which is what we hint at in our article.
  • 11 Hide
    blubbey , December 24, 2012 8:43 PM
    tipoo I'm thinking in the coming years, Intel vs ARM will become a more interesting battle than Intel vs AMD.


    I was until I saw the numbers. Intel spent $8.4 billion in 2011 ($6.6 billion in 2010 and $5.7 billion in 2009) on R&D - http://www.intc.com/intelAR2011/business/research/ - while ARM isn't worth $1b. It may take a few years but Intel are seriously massive, they'll soon be the go to guys for mobile. Plus (according to rumours) with Haswell focusing on power saving, it could be a big leap forward.
  • 5 Hide
    tipoo , December 24, 2012 8:45 PM
    AlanDang@tipoo, we're not going to hang our hat on it just yet (until we run the numbers ourselves), but A15 runs hot, which is what we hint at in our article.


    I'm guessing the same thing. So far we've only seen it in a tablet (Nexus 10), and even that with its 10 inch tablet sized battery didn't last particularly long. ARM has the distribution advantage right now, but I think once Intel gets its foot in the door it will be the 900lb gorilla in this market as well.
  • 0 Hide
    Anonymous , December 24, 2012 8:57 PM
    ARM isn't just ARM holdings, it's nVidia, Samsung, and Qualcomm just to name a few of the heavy hitters. And it should also be noted that even if your SoC is better, if the OEM integrating it is incompetent, it won't matter. I'm certain more Surface RT devices have been sold compared to the Acer W500 because it had better availability, a stronger marketing campaign, and overall is a far more solid device. Don't miss the forest for the trees.
  • 4 Hide
    tipoo , December 24, 2012 8:59 PM
    blubbeyI was until I saw the numbers. Intel spent $8.4 billion in 2011 ($6.6 billion in 2010 and $5.7 billion in 2009) on R&D - http://www.intc.com/intelAR2011/business/research/ - while ARM isn't worth $1b. It may take a few years but Intel are seriously massive, they'll soon be the go to guys for mobile. Plus (according to rumours) with Haswell focusing on power saving, it could be a big leap forward.


    Didn't Qualcomm alone overtake AMD as a chipmaker? The thing about ARM is that anyone can get a licence for the ISA and build a custom core around it, like Krait.
  • 14 Hide
    AlanDang , December 24, 2012 8:59 PM
    And the Chromebook with an A15. We're looking at several other SoC's but what's empowering is how simple math can help you look at efficiency.

    But it's Christmas Eve, and sometimes there are more important things than running benchmarks and soldering wires to SoCs. ;) 
  • -5 Hide
    richarduk , December 24, 2012 9:14 PM
    Measurements taken when running Windows. Arm and Intel chips both require different coding styles to make them preform. The way windows has been coded favours the Intel Arch. Intel chips like to lean heavy on their cache, Arm chips prefer code to do as much processing on it's data as it can using all it's registers before moving on.

    Bit like comparing a 4x4 and a sports car in a muddy field.

  • -3 Hide
    darkchazz , December 24, 2012 9:23 PM
    nvidia tegra 3 is a piece of overhyped garbage.
  • 16 Hide
    tomfreak , December 24, 2012 9:47 PM
    of all the ARM types, u took one of the weakest one? I like to see the numbers vs Qualcomm krait and Apple's A6
  • -5 Hide
    jonjonjon , December 24, 2012 9:51 PM
    down with arm! if i ever do use a tablet (wont be anytime in the foreseeable future) i want to be able to run x86 programs.
  • 8 Hide
    esrever , December 24, 2012 10:32 PM
    just another article showing how much of a piece of crap tegra is.
  • 3 Hide
    fudoka711 , December 24, 2012 10:55 PM
    I agree that it will be interesting to see ARM based tablets/phones to battle with upcoming Intel Atom cpu's in tablets (and phones?). Intel's really stepping up their game and it'll just force ARM to step up theirs.

    We're already at quad-core ARM SoC's running at up to 1.7ghz. My understanding is that they won't be able to run too much faster anymore and will instead have to do more work per cycle. I think that's where Atom has the advantage in this case, which is why they can run slower but still accomplish the same amount of work with less power (but not faster).

    If only this would translate into the Desktop/Laptop sector. We haven't had huge performance gains in the longest time. I miss the old days of Athlon 64...
  • 8 Hide
    Anonymous , December 24, 2012 11:06 PM
    Once again, Intel manages to sort of tie with a middle-of-the-pack last-generation ARM CPU, well done.

    Tegra 3 is junk and everybody knows it, bring on the Samsung Chromebook or a comparable tablet running an A15, and run Linux on them. Or rather than just waiting for Tom's to do it, check out the benchmarks on Phoronix that show the A15 eating the Atom for breakfast...
  • 5 Hide
    AlanDang , December 24, 2012 11:30 PM
    @jessica. Phoronix tested the older Atom which we note has the same name but nowhere near the same performance or energy efficiency. Also keep in mind that Phoronix didn't actually try to run their benchmarks off the battery. A15 is fast, but the performance isn't free.

    The advertised battery life on a Chromebook is very telling. It gets 6.5 hours of web browsing with a 30 watt-hour battery, so it's drawing 4.62W under that workload. This Atom tablet is drawing closer to 3.11W under an average web browsing workload and the Tegra 3 is drawing about 3.9W. We're looking at Snapdragon next and then A15, but I think everyone's going to be surprised once they look at the actual numbers when you're running apps other than Phoronix's benchmarks.
  • 2 Hide
    Anonymous , December 24, 2012 11:35 PM
    Alan: But the new mobile Atom is slower than the old netbook Atom, which is why you never see them in the same benchmark. Those power savings weren't free, and yet the A15 still destroys either Atom.
  • 7 Hide
    AlanDang , December 25, 2012 12:35 AM
    Geekbench would argue differently.

    Atom Z530 (the "Z-class" Atom Phoronix tested).
    http://browser.primatelabs.com/geekbench2/search?utf8=%E2%9C%93&q=z530

    Atom D525 (the fastest netbook Atom Phoronix tested, which beats Exynos Dual in some applications)
    http://browser.primatelabs.com/geekbench2/search?utf8=%E2%9C%93&q=d525

    http://www.phoronix.com/scan.php?page=article&item=samsung_exynos5_dual&num=5

    Atom Z2760
    http://browser.primatelabs.com/geekbench2/search?utf8=%E2%9C%93&q=z2760

    The Atom D525 had a TDP of 15W in 2010. The Atom Z2760 has the same performance with a TDP of
  • 8 Hide
    AlanDang , December 25, 2012 12:37 AM
    less than 2W. The Exynos has a TDP of 4W.

    If the A15 is 2x the power consumption, is it consistently 2x as fast?
  • -4 Hide
    Anonymous , December 25, 2012 12:51 AM
    Jessica... you couldn't be more wrong. Good grief!
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