Articles: CPU

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Power Consumption

Systems based on processors with integrated graphics cores become increasingly popular not only due to possible system miniaturization. In most cases the users decide to go with them, for cost-cutting purposes. Processors like that help to save some cash not only by omitting the external graphics accelerator, but also by allowing to build a more energy-efficient system with total power consumption being lower than that of a system with discrete graphics. There is another bonus to it: quiet operation modes, because lower power consumption leads to lower heat dissipation and therefore the use of simpler cooling systems.

Therefore, the developers of processors with integrated graphics do their best to minimize the power appetites of their products. Most CPUs and APUs discussed today have about 65 W TDP, which has already become an unofficial standard. However, we know that Intel and AMD have different approach to TDP that is why it will be interesting to check out the practical power consumption of systems based on different processors.

The graphs below show two power consumption readings. The first one is the full power draw of the computer (without the monitor) measured after the power supply. It is the total of the power consumption of all the system components. The second one is the power consumption of the processor alone measured along the individual 12 V power line. In both cases the PSU's efficiency is not taken into account, because our measuring equipment is installed after the PSU and registers only voltages and currents that get into the system along 12, 5 and 3.3 V lines. The CPUs are loaded by running the 64-bit LinX 0.6.4 utility. We used FurMark 1.9.1 to load the graphics cores. We enabled all the power-saving technologies and Turbo Core (where available) for correct measurement of the computer's power draw in idle mode.

In idle mode all systems consumed about the same amount of power. As we can see, Intel processors barely load the processor power line in idle mode, while AMD APUs, on the contrary, consume up to 8 W along the 12 V CPU power line. However, it doesn’t mean that Fusion solutions can’t go into deep power-saving modes. These differences come from different implementations of the processor voltage regulator circuitry: Socket FM1 systems use processor power line to feed the computational and graphics cores as well as the integrated chipset North Bridge, while in Intel systems the chipset North Bridge is powered by the mainboard.

Under maximum computational load AMD processors experience some energy-efficiency issues, the same as we saw by Phenom II and Athlon II: they didn’t go anywhere even with the introduction of the finer 32 nm process. Llano processors are based on the same microarchitecture as their predecessors, and lose to Sandy Bridge competitors in terms of performance-per-watt just as badly. Top Socket FM1 systems consume about twice as much as LGA1155 systems with Core i3 inside, while the computational performance of the latter is obviously way higher. The power consumption difference between Pentium and junior A4 and A6 APUs is not so dramatic, but the overall situation still remains the same.

Things do not change under heavy graphics load: Intel processors are significantly more energy-efficient. But in this case, AMD Fusion boasts much higher 3D performance, which could justify as some excuse. Note that Core i3-2125 and A4-3300 produced the same fps in gaming tests and were very close to one another in terms of power consumption under heavy GPU load.

When all units of the hybrid processors are loaded simultaneously, we get the score that may be regarded as a sum of two previous graphs. A8-3850 and A6-3650 processors with 100 W TDP distance themselves significantly from the rest of the 65 W AMD and Intel products. However, even without them, AMD Fusion processors are still less energy-efficient than the Intel CPUs in the same price range.

If the processors become part of a media center used primarily for HD video playback, the situation turns very uncommon. The computational cores are mostly idling in this case, and the video stream decoding is done in special units within the GPU. Therefore, AMD based platforms achieve pretty decent energy-efficiency and their power consumption doesn’t exceed that of Intel Pentium and Core i3 based platforms too much. Moreover, AMD A6-3500 processor with the lowest clock frequency of all becomes the most energy-efficient choice in this usage scenario.

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