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Atom: In-Order and HyperThreading

Intel Atom CPU Review
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The Atom uses a new architecture, but with older technologies. It’s the first in-order x86 from Intel since the Pentium, back in 1993. All other Intel processors (since the P6) use an out-of-order architecture.

In-Order: Say what?

intel atom

To simplify, think of the processor as receiving the instructions one by one and putting them in its pipeline before executing them. In an in-order architecture, the instructions are executed in the order in which they arrive, whereas an out-of-order architecture is capable of changing the order in the pipeline. The advantage is that losses can be limited. If, for example, you have a simple calculation instruction, a memory access, then another simple calculation, an in-order architecture will execute the three operations one after the other, whereas in OoO the processor can execute the two calculations at the same time and then the memory access, with an obvious time saving. Quite surprisingly, whereas in-order architectures generally use a short pipeline, the Atom has a 16-stage pipeline, which can be a disadvantage in certain cases.

HyperThreading

intel atom

HyperThreading is a technology that appeared with the Pentium 4. It can process two threads simultaneously using the unused parts of the pipeline. While not as efficient as two true cores, the technology can make the OS think that the CPU can process two threads simultaneously and increase the computer’s overall performance. On the Atom with its long pipeline coupled to an in-order architecture, HyperThreading is very effective, and the technology can significantly increase performance without impacting the TDP. Intel claims an increase in consumption of only 10%.

The processing core

intel atom

For the rest, the Atom is equipped with two ALUs (units capable of performing integer calculations) and two FPUs (units dedicated to floating-point calculation and very important for gaming, for example). The first ALU manages shift operations, and the second jumps. All multiplication and addition operations, even in integers, are automatically sent to the FPUs. The first FPU is simple and limited to addition, while the second manages SIMD and multiply/divide operations. Note that the first branch is used in conjunction with the second for 128-bit calculation (the two branches are in 64 bits).

Intel Has Optimized the Basic Instructions

If you look at the number of cycles necessary to execute instructions, you realize something: Some instructions are fast and others are (very) slow. A mov or an add, for example, is executed in one cycle, as on a Core 2 Duo, whereas a multiplication (imul) will take five cycles, compared to only three on the Core architecture. Worse, a floating-point division in 32 bits, for example, takes 31 cycles compared to only 17 (or almost half as many) on a Core 2 Duo. In practice – and Intel willingly admits this – the Atom is optimized to execute the basic instructions quickly, meaning that this processor short-changes performance with complex instructions. This can be checked simply using Everest (for example), which includes a tool for measuring the latencies of instructions.

intel atom

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  • 1 Hide
    anonymous x , June 6, 2008 1:10 AM
    wow, 107 on 3D mark06
  • 0 Hide
    joefriday , June 6, 2008 2:03 AM
    Celerons have significantly lower frequencies than Atom? umm...no. Only the ULV celeron M has a lower freqency. Modern notebooks start with Celerons at least 1.6GHz, more likely 1.86GHz, and are built on the much more modern Merom architecture, which have at least a 10% IPC advantage over the old Dothan architecture. No, atom is nowhere NEAR a modern Celeron in performance. Nice try though.
  • 4 Hide
    joefriday , June 6, 2008 2:06 AM
    Also, Why not have a Celeron 420 by now? Are you telling me that THG, with all its money, can't budget in a $30 CPU for comparative testing?
  • 4 Hide
    joefriday , June 6, 2008 2:41 AM
    After reviewing the article, I can say I'm thoroughly unimpressed with the Atom platform (at least the current desktop derivative). If anyone can remember, THG did a $300 PC build using now ancient Celeron Ds and AMD Semprons. One thing that I find amazing, is that those old rigs both use LESS power than this Atom desktop rig.
    http://www.tomshardware.com/reviews/the-300-pc,1546-10.html

  • -1 Hide
    randomizer , June 6, 2008 3:48 AM
    Don't you people understand that Atom is not a desktop processor? You can't compare its performance to a desktop processor fairly because that's not what it is designed for.
  • 1 Hide
    joefriday , June 6, 2008 4:26 AM
    This Atom CPU is on a desktop board. That means it's fair game, especially when the processors being compared are also comparable in price.
  • -5 Hide
    randomizer , June 6, 2008 4:43 AM
    It's on a desktop board, woopdedoo. If you could get your mobile phone processor to run on a desktop board would you compare it to an E2160?
  • 1 Hide
    joefriday , June 6, 2008 5:34 AM
    Who cares what the Atom CPU is SUPPOSED to be. It is right now, in this review, on a desktop-oriented package, built to compete with low power consumption desktop computers. It fails miserably in that regard, as it is neither low power consumption, nor competitive. In your ridiculous example, if I had a mobile phone processor on a desktop board, and it ended up consuming more power than an E2160/motherboard combo that costs the same amount of money, all the while performing much worse than the e2160, I would call the mobile phone cpu on a desktop motherboard either A FAILURE or AMD. Take your pick.
  • 1 Hide
    apaige , June 6, 2008 6:35 AM
    So, for the Intel Atom, you do use an updated version of Sandra, but not for the Phenom. You compare it to the VIA C7, a 3 year-old CPU, but not the VIA Nano, which will be available in the same timeframe as the Atom. You don't provide graphics for power consumption, despite the Atom being designed for low power consumption; surprise, the old C7-M system draws less power.

    Biased much?
  • 1 Hide
    Anonymous , June 6, 2008 8:10 AM
    Not sure that Nano's are really available yet, still a newer mini-itx based C7 (say EPIA-M700) would have been better, since you would be looking at even less power than the one used and the VX800 will end up used with the Nano. The D201DLY[2] would have been good to compare to, would also give some idea how the Atom would go paired with SiS chipsets.
  • 0 Hide
    Crazy-PC , June 6, 2008 9:43 AM
    Why not benchmark with other mobile CPUs like Intel X-scale and the mobile CPU from TI etc Atom would be more make sense to use on small mobile device rather than notebook.
  • 3 Hide
    Anonymous , June 6, 2008 10:32 AM
    randomizerDon't you people understand that Atom is not a desktop processor? You can't compare its performance to a desktop processor fairly because that's not what it is designed for.


    His point was that it's not only less powerful than "comparable" desktop CPUs, it also takes more power, which pretty much defeats the meaning of being used as a CPU in portable applications. His point is that this CPU is unimpressive in every area you could apply it versus what's already there. Nice try, Intel.
  • 0 Hide
    Anonymous , June 6, 2008 11:37 AM
    VIA Nano powered by Nvidia GPU in mini-itx play game: Crysis and Bioshock.
  • 1 Hide
    Anonymous , June 6, 2008 12:20 PM
    ??? INTEL ATOM vs. VIA NANO ???
  • 2 Hide
    Wheat_Thins , June 6, 2008 1:27 PM
    Where the heck is the performance / watt comparisons. The entire point of this processors creation is performance / watt and its missing from your benchmarks! Please Add!
  • 0 Hide
    mmc4587 , June 6, 2008 1:59 PM
    Dude, please correct your Cinebench R10 charts, they are screwed up.

  • 0 Hide
    joefriday , June 6, 2008 3:47 PM
    Quote:
    His point was that it's not only less powerful than "comparable" desktop CPUs, it also takes more power, which pretty much defeats the meaning of being used as a CPU in portable applications. His point is that this CPU is unimpressive in every area you could apply it versus what's already there. Nice try, Intel.

    Don't get me wrong...I do think the Atom probably has a decent performance per watt for the CPU itself, but this platform being tested, the entire rig, is where it disappoints. I don't know if it's all in the PSU inefficiency or what, as Anandtech's review of the ASUS Eee Box put power consumption at below 20 watts under load, using a seemingly comparable hardware list (but with a DC power brick, instead of a conventional power supply).
  • 0 Hide
    enewmen , June 6, 2008 6:02 PM
    Good article.
    Still don't know if it's POSSIBLE to run Vista64 on a Atom.
    I'll wait for the next-gen of eee PC clones. Then I'll get a better idea of real-world performance.
  • 0 Hide
    Anonymous , June 6, 2008 7:12 PM
    NVIDIA Tegra is much Better
    It would be interesting to see their response at the Intel Atom Processor Launch Event on June 3rd, 2008*. In the meantime, let's take a look at what the NVIDIA Tegra is all about... why ? lets see
    * an 800 MHz ARM CPU,
    * a HD video processor,
    * an imaging processor,
    * an audio processor,
    * and an ultra-low power GeForce GPU
    for father information plz go to http://www.techarp.com/showarticle.aspx?artno=549&pgno=0
  • 0 Hide
    doomsdaydave11 , June 6, 2008 7:34 PM
    Yay the Poulsbo processor is named after where I live :D . There is only one Poulsbo... so it must be. I'ma go out and buy one now. ;) 
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