ARM Vs. x86: The Secret Behind Intel Atom's Efficiency

Putting Hard Numbers Behind Mobile Power Consumption

Andrew Ku has been in the process of reviewing a couple of new tablets: Samsung's ATIV Smart PC 500T, with an Atom Z2760 inside, and Samsung's ATIV Tab, with Qualcomm's APQ8060A. I've been playing with Acer's Atom-powered Iconia W510, and my initial thoughts on that will go live soon.

One thing both Andrew and I are impressed with is that the Atom-based tablets, running full versions of Windows 8, compete readily with Microsoft's Tegra 3-powered Surface when it comes to battery life, and doubly so when you consider Acer's W510 only has a 26.6 Wh battery compared to the Surface's 31.5 Wh power source.

The sensitive stuff is blacked-out to protect the innocent

As far as performance goes, the Atom Z2760 (code-named Clover Trail) trades blows with Nvidia's Tegra 3 in our Geekbench numbers, but then completely blows it away in our Web browsing metrics. The fact that it's able to run x86-based apps fairly well is a clear benefit, too.

So, how do you get dramatically better performance in certain tests, and then competitive run time in those same workloads, all from a smaller battery? Answering that question would have been quite a challenge. But then we asked Intel to show us some of the advanced equipment in its own lab, which allows the company to take very granular measurements.

While we were up in Santa Clara last week, Intel presented us with data its performance analysis team had generated, showed us how it generated that information, letting us play with the test equipment ourselves, and discussed with us in great depth Clover Trail's strengths and weaknesses. Again, the following numbers come from Intel's team, not the Tom's Hardware lab. We did confirm that all displays were standardized to 200 cd/m2 (nits) using a Gossen Luminance meter, though, and power consumption is reported as the average over a 50 millisecond time slice. During the course of this piece, we'll break down Intel's numbers and compare them what we've done in our own offices, looking for connections.

Swipe to scroll horizontally
Idle: Microsoft Surface
Row 0 - Cell 0 Platform (W)CPU (W)GPU (W)Memory (W)Panel Backlight (W)Everything Else (W)
System Idle (Ideal): Windows 8 UI2.820.00380.210.250.981.38
System Idle (Ideal): Desktop3.000.00470.210.251.111.42
System Idle: Split Screen3.640.290.310.371.111.56
Swipe to scroll horizontally
Idle: Acer W510
Row 0 - Cell 0 Platform (W)CPU (W)GPU (W)Memory (W)Panel Backlight (W)Everything Else (W)
System Idle (Ideal): Windows 8 UI2.470.020.110.290.841.22
System Idle (Ideal): Desktop2.760.020.110.301.091.24
System Idle: Split Screen3.370.180.240.361.141.45

For each tablet, Microsoft's Surface and Acer's W510, we're looking at power consumption on the Windows 8 UI, the Windows 8 Desktop, and a split-screen scenario, where a Windows 8 app is open on one side and the Desktop is open on the other. In this case, the Windows 8-style app is the primary screen and the Desktop functions as the sidebar.

The first column to pore over is the usage of each CPU. Tegra 3 delivers a very impressive idle processor draw of 0.0038 W in the Windows 8 UI interface, compared to the Atom's .02 W. But running in split-screen mode uses a lot more power. Tegra 3 jumps to .29 W, ahead of the Atom's .18 W.

Next up is the GPU. Now, we already know that the single-core PowerVR SGX545 in Intel's chip is quite a bit slower than Tegra 3 in 3D graphics. But at least in the 2D applications you run on both SoCs, the Atom's simpler graphics engine uses less power across the board.

Wired up to the requisite microsolder points.

The first hint of Intel's efficiency advantage comes from the memory column. At first glance, the Atom looks worse-off than Tegra. But remember that the Atom Z2760 sports two 32-bit memory controllers with LPDDR2-800 support, delivering up to 6.4 GB/s of bandwidth. The T30 found in most devices boasts a single-channel controller able to address DDR3-L at up to 1500 MT/s, yielding up to 6 GB/s. In theory, though, Intel's Atom has to do more work, suggesting its memory subsystem also operates more efficiently.

The rest of the platform includes the screen itself and panel electronics (like the LVDS transmitters), along with wireless radios, audio codecs, NAND, and anything else going on under the hood. Even in a scenario where Acer’s backlight eats up more power (operating in split screen mode), the rest of its platform is still 0.10 W more efficient.

  • Novuake
    Excellent! Was wondering about this for some time. Also made the mistake of thinking Intel was behind in the mobile space... Well done Toms.
    Reply
  • tipoo
    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.
    Reply
  • 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.
    Reply
  • blubbey
    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.
    Reply
  • tipoo
    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.
    Reply
  • 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.
    Reply
  • tipoo
    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.
    Reply
  • AlanDang
    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. ;)
    Reply
  • richarduk
    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.

    Reply
  • darkchazz
    nvidia tegra 3 is a piece of overhyped garbage.
    Reply