Idle Power

In all of these tests you're going to see three charts. The first will show you total platform power, measured at the battery, taking into account everything from SoC to display. The next shows you power measured at the CPU power delivery circuit, and the third shows you power measured at the GPU power delivery circuit. All values are measured in watts, and are reported in 15ms intervals (although I sampled at 1KHz then averaged down to 15ms).

For our first set of tests I simply wanted to get a feel for idle power. Both systems had all background syncing suspended, WiFi was connected, and we're just sitting at the Windows RT/8 Start Screen until the tablets reached a truly idle state. Note that idle under Windows RT/8 technically doesn't happen until the live tiles stop updating, which you'll see denoted by a drop in the idle power consumption in the graphs below.

First up is total platform power consumption:

Surface RT has higher idle power, around 28% on average, compared to Acer's W510. The last half of the graph shows the tablets hitting true idle when the live tiles stop animating.

A look at the CPU chart gives us some more granularity, with Tegra 3 ramping up to higher peak power consumption during all of the periods of activity. Here the Atom Z2760 cores average 36.4mW at idle compared to 70.2mW for Tegra 3.

The GPU specific data is pretty interesting - the GPU power rail shows much high power consumption than on Intel's Z2760. As I didn't design Tegra 3, I don't know what else is powered by this rail - although you'd assume that anything else not in use would be power gated. Imagination Technologies' PowerVR SGX 545 does appear to be quite power efficient here, on average using 155mW while rendering the Start Screen.

I wasn't happy with the peaks we were seeing when nothing was happening on the systems, so to confirm that nothing funny was going on I threw both tablets into airplane mode and waited for full idle. Check out the tail end of the platform power diagram:


That's much better. Without the AP talking to each tablet's WiFi radio constantly, idle becomes truly idle. If you're curious, the power savings are around 47.8mW (average) for the W510 in airplane mode when fully idle.

The GPU rail feeding the Atom Z2760 appears to hit a lower idle power when compared to NVIDIA's Tegra 3. Advantages in idle power consumption are key to delivering good battery life overall.

Introduction OS & App Launch Power


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  • dc77gti - Tuesday, December 25, 2012 - link

    Looking forward to 22nm Bay Trail-T. Hopefully Intel can get this out before 2014.
    That's half the battle. The other half lies with Google Android. We'll have to wait and see. With Intel's hardware might and Android's open source project, things will get more exciting.
  • kyuu - Wednesday, December 26, 2012 - link

    *sigh* Everyone seems to have forgotten about AMD's Temash which should be out by mid-2013... hopefully. Hell, I'd even take a Hondo tablet over Clover Trail, if anyone actually made one. Reply
  • thebeastie - Tuesday, December 25, 2012 - link

    I don't know about this.. all of a sudden the tables have turned against ARM?
    Mythbusters do a pretty thorough job on testing, I want them to do the same round of testing on these chips and see what THEY come up with.

    Apples A6 still reams the Atom so its not really that great.

    Anyway ARMs real kryptonite has been price. Intel might sell thee chips cheap as a last ditch stand one off or two off but they can't do it forever before what matters to them most falls apart.... and thats making a lot of money.
  • puppies - Wednesday, December 26, 2012 - link

    I think most of us realise that intels biggest problem right now is that in the desktop environment (their main source of income from the public) a 3 or 4 year old chip is more than adequate for 99% of tasks that the average pc user wants to perform. Software just isn't being developed (or is there much need for it) that requires a quad core 3.5ghz cpu with turbo and HT when a 2.5ghz dual core will more than suffice.

    If however they can push the performance envelope of these ultra low voltage parts to a point where software starts being developed that can utilise those chips to their potential then ARM will not be a viable option for anyone who needs that performance.

    Most tablet reviews state something along the lines of "it is ok for a few last minute corrections to a presentation but you might want something more powerful for when you aren't on the train/plain etc". If intel changes that to "This ultra portable tablet has enough grunt for all your word/powerpoint/excel creation needs" and ARM can't keep up then Intel becomes the required CPU for business users, intel really doesn't care about $200 tablet sales. They are generally bought as presents for kids and there just isn't the profit available that intel seems to desire.

    Combine this with the fact that no company is going to want to deal with the headache of trying to sync workloads between X86 office pcs and ARM based ultra portables and intel suddenly has a reason to charge the big bucks again.
  • FunBunny2 - Friday, December 28, 2012 - link

    I expect the reality is: for consumers, the need for anything much more than a 486 is, well, past. Not much computation outside of Excel. Pretty pixels, on the other hand...

    If M$ could write a yet more bloated OS, then the old Wintel symbiotic monopoly might return. Fact is, we're still where Xerox PARC put us 3 decades ago. The hardware isn't much different, save for touch, either. There was a time when PCs shipped with monochrome tubes, by default. And the OS was a command line ark.
  • war59312 - Wednesday, December 26, 2012 - link


    This image as linked on page 5, the very last image appears to be broken:


  • Veteranv2 - Wednesday, December 26, 2012 - link

    Reading this review, it makes me realize how websites are abused as a marketing gimmick.

    Keep this in mind:
    - It is all teste on Win8.
    - Win8 is primarely Win7 but with ARM support
    - Windows has been optimized for X86 in any way, they just recently added support.
    - Who says ARM support on Win8 is any good for ARM performance? It is compatible, but x86 has enjoyed +20 years of optimization

    If anandtech would have wanted to do this right they would have used this:
    - A6X or A15 ARMcores

    What has anandtech proven:
    - Win8 is bad for ARM
    - Tegra3 on 40nm has worse power consumtion then a 32nm part
    - It is a marketing tool for intel which is struggling in the tablet market and needs positive things like this
    - That it cannot objectively make differences clear between architectures, cause this review has nothing to do with architectures...

    A sad day for anandtech...
  • thebeastie - Wednesday, December 26, 2012 - link

    I guess I could agree with this, Anandtech is my absolute favorite tech site for the truth but some times he just seems to be a little bit too much of an Intel fan. But alternatively I do see that he is ready to hand out credit where it is due, and Intel is all too often the company to beat.

    Ultimately I think his heading was a poor choice of words and is just as much appeared to be skewed towards headline grabbing as much has being an accurately balanced review.

    I guess that will always be part of the game with "the press"
  • CeriseCogburn - Friday, January 25, 2013 - link

    You guys missed the bucket of fudge, and forgot the nvidia hate.

    Thus the Tegra3. you've missed the bias boat, bros.

    Anand got screwed on nVidia gpu's a long while back, and they AND Tom's have never forgotten the slight.

    It was the (made notorious) "rebranded" nVidia 9800x, where Anand just reused another of the nVidia gpu's they had in house and adjusted the clocks and claimed they thus tested the "new" nVidia release.

    The deep hatred has been seething here ever since, in every article, pumping up the amd fanboys, and only recently has that latter group somewhat receded, due to continual epic fails by amd.
  • powerarmour - Friday, December 28, 2012 - link

    Agreed Reply

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