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• Efficiency: Core 2 Nukes Atom On The Desktop

  The time when the processor and platform markets were simply divided into desktop, server, and mobile hardware segments is long gone. Mobile products and related technologies have entered the enterprise and home markets to increase efficiency. Server technology increasingly meets the demand of enthusiasts. And OEMs are adding desktop components to mobile computers to reduce costs. In short, the same platforms and technologies are adopted for multiple different applications rather than specialized market segments. However, a new generation of hardware has emerged. Geared toward the mobile and low-cost audiences, these new solutions address the needs of shrinking system dimensions, cost pressures, and ultra-mobile system requirements. VIA’s C7 and Nano processors have been around for a while, but it’s Intel’s Atom that is widely being adopted for low-cost solutions and netbook-type devices, along with nettops. However, while Atom certainly is great for mobile devices with limited performance requirements, we found that its system power consumption can be matched by a mainstream Core 2 Duo system–-which also offers a significant performance boost. Core 2 Doesn’t Do It All We don’t want to give you the wrong impression with this article, so it’s important to clearly define the purpose and difference between the Atom and Core 2 processors. Core 2 is Intel’s mainstream flagship product for PCs and notebooks. It is a processor that has to be installed in a socket. Models are available with two or four processing cores with large, medium, or small cache capacities and varying system speeds. Currently, Core 2 processors cover the full spectrum, from maximum performance to maximum mobility and power efficiency for PC systems. However, Core 2 processors are complex and somewhat power-hungry. Although they are efficient, Extreme models require up to 130 W, which means that substantial cooling is required. What Atom Is All About Atom was developed to be cost-effective from the beginning (for Intel and its customers), to deliver a certain minimum performance, and to serve as a low-power part. While Atom is Intel’s smallest processor, the chip giant also touts its very low power specs: the desktop single cores are rated at 4 W, while the mobile versions are rated at only 2 W. The Atom 330 dual core is even rated at only 8 W. All Atom processors have to be soldered onto a motherboard by the manufacturer, which means that they are incapable of supporting any future upgrades. On the other hand, Atom retails for only $20-$70, which is a quarter to half of the cost of an entry-level Core 2 processor. Unfortunately, Atom isn’t really fast, which makes it clear that it should not be used for systems that have to deal with anything that is more demanding than YouTube video playback, checking email, or browsing Web sites. Atom Vs. Core 2: The Efficiency Shootout We thought about this comparison when we looked at two G31 motherboards using a Core 2 Duo E7200 processor, as one of the platforms was capable of consuming only 31 W of power at the plug with the use of an efficient power supply unit. After we saw the 28 W idle power level of the Atom system that we used in the comparison between Atom and VIA’s Nano, we became curious about which CPU was really more efficient. Efficiency is not measured by the lowest power level a CPU can maintain, but it is instead determined by its performance–per-power consumption ratio. We wanted to know if we could match the Atom’s system idle power consumption to that of a Core 2 Duo system and find out the real efficiency champion.

• It is quite clear that the 945GTC-D board from ECS with the Intel Atom 230 processor is not suitable for use as a desktop workstation. Although the integrated graphics core would be sufficient, the speed of the Atom 230 processor is just too slow for day-to-day desktop tasks. Of course, not every user will agree. If you know the precise utilization of the system and you have enough experience to assess what level of computer performance is required, you may find that this system meets your needs perfectly. But this only applies to certain special types of use. For example, it is possible to surf quite happily as long as the right operating system is used (Windows XP or Linux). If you run more than one application at a time, though, the Atom system will slow down. The power consumption of the Atom board in both idle mode and under full load set new records in our Munich test lab. The minor advantage over other platforms is a bit disappointing, though. An AMD Sempron LE-1100 system only requires 3 watts more energy in idle mode. On the other hand, under full load, the Atom only jumps by a few watts, while the other desktop-tuned processors consume far more energy. Anyone who tends to have a system that mainly sits idle will not notice a major difference between the energy consumption of the Atom and the Sempron LE-1100 system. This is, for example, the case when a computer is mainly used for downloads. The desktop version of the chipset used is largely to blame for this. Since the Diamondville-based Atom system for the desktop is only currently available with an energy-hungry desktop chipset, much of the advantage of the very low energy consumption of the Atom 230 goes to waste. Maybe a motherboard manufacturer will take the plunge and build a Diamondville board based on a mobile chip set. The dual memory interface doesn’t provide much performance advantage, either. The idea from Intel to integrate Hyper-Threading was absolutely right, as it allows the Atom to improve its performance in our tests by up to 37%. But the Atom has lower computing power compared to the current AMD and Intel platforms. We’d recommend checking out one of those before toying with an Atom-based desktop.

• Power consumption is central to this Intel platform, and they’ve made a lot of efforts in that department. Aside from the chipset, which consumes a lot of power in comparison to the processor, the Atom itself has many attractive functions. Bus and cache As we’ve already said, Intel has put a lot of effort into the bus and the cache: A different mode for the bus was developed (CMOS mode) and the cache can be disabled in part depending on how it’s being used. These functions reduce power consumption, as do the use of an in-order architecture and 8T SRAM for the L1 cache. C6 power state In addition to the low voltage (1.05 V) CPU, the Atom also introduces a new standby mode, C6. As a reminder, the C modes (0 to 6) are low-power states, and the higher the number, the less the CPU consumes. In C6 mode, the entire processor is almost totally disabled. Only a cache memory of a few kB (10.5) is kept enabled to store the state of the registers. In this mode, the L2 cache is emptied and disabled, the supply voltage falls to only 0.3 V, and only a small part of the processor remains active, for wake-up purposes. The processor can go into C6 mode in approximately 100 microseconds, which is quick. In practice, Intel claims, C6 mode is used 90% of the time, which limits overall power consumption (obviously, if you launch a program that requires a lot of CPU power or even watch a Flash video you won’t be in that mode). We should point out, though, that the two chipsets to be used with the Atom N200s are power users: the Atom 230s use a i945GC that consumes 22 W (4 W for the CPU) and the Atom N270s ship with a i945GSE that burns 5.5 W (2.4 W for the CPU). In Practice So is the Atom really low-power in practice? The processor is, yes. For the platform aimed at NetTop (low-cost desktop computers), the answer is yes, but... Why the “but”? Because the chipset used uses a lot of power and the processor is listed at a TDP of 4 W, compared to 2.4 W for the mobile versions. Our test motherboard consumes 59 W in standby, and we reached 62 W under maximum load (with a 3.5" hard disk and a 1 GB DDR2 DIMM). Obviously, these values are what we measured for the complete platform, not only the motherboard, and they don’t take power-supply losses into account (our test model has a yield of approximately 80%). That’s both a little and a lot – it’s not much for a desktop computer, of course, but it’s a lot in absolute terms. We should add that we recently tested a motherboard based on a 1.5 GHz Via C7, and the configuration drew less power with the same components: 49 W at idle and 59 W under load (always measured at the AC outlet).