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Power Consumption

When we talked about the FX-8350 processor, we arrived at the conclusion that Piledriver microarchitecture didn’t improve the energy-efficiency of the Socket AM3+ processors that much. AMD’s products manufactured with 32 nm process remain quite power-hungry compared with the 22 nm competitors. However, Vishera modifications reviewed today work at lower clock frequencies and have fewer cores, so they may turn out more energy-efficient than the flagship processor. Especially, since six- and quad-core modifications have 95 W maximum TDP instead of 125 W TDP of their “fully-fledged” brothers.

To find out more about the power consumption of all current processor models in the new AMD FX family, we performed a round of special tests. The new digital power supply unit from Corsair – AX1200i – allows monitoring consumed and produced electrical power, which we use actively during our power consumption tests. The graphs below (unless specified otherwise) show the full power draw of the computer (without the monitor) measured after the power supply. It is the total power consumption of all the system components. The PSU's efficiency is not taken into account. The CPUs are loaded by running the 64-bit version of LinX 0.6.4-AVX utility. Moreover, we enabled Turbo mode and all power-saving technologies to correctly measure computer's power draw in idle mode: C1E, C6, Enhanced Intel SpeedStep and AMD Cool’n’Quiet.

In idle mode all processors and platforms consume about the same power. In idle mode any contemporary processors will switch to special power-saving states, in which their power consumption will be very low – only a few watts. In this case the power appetites of other system components and the efficiency of the voltage regulator circuitry on the mainboard start to matter more and they partially mask the pure processor power consumption.

In case of single-threaded load things start going south for AMD processors. The fastest and most energy-hungry LGA 1155 Core i7-3770K consumes considerably less power than the most energy-efficient AMD FX product. At the same time, AMD processors work slower under this type of load than Intel CPUs. Yes, Vishera generation doesn’t waste the energy the way Zambezi processors used to, but there is still no visible indication of a qualitative change.

The situation doesn’t get any better when it comes to AMD FX power consumption under multi-threaded load either. FX-8350 turns out the most power-hungry CPU in our today’s test session. It consumes 4% more power than FX-8150 under maximum load and is 2/3 more power-demanding than Intel Core i7-3770K. Other members of the FX family on Vishera design do a little better compared with their predecessors, but they are still incomparable with any of the competitive offerings. At the same time, I have to say that FX-6300 and FX-4300 with 95 W TDP do look much batter against the background of all other Socket AM3+ processors. Had we also tested the old Core i5 processors manufactured with 32 nm process, then the new dual-module quad-core AMD processor would have been comparable against them in power consumption. Although in terms of performance this comparison makes absolutely no sense.

In other words, it looks like contemporary AMD processors are hopelessly behind their Intel competitors in terms of performance-per-watt. While in performance tests top eight-core Vishera processors can sometimes compete successfully against Intel’s quad-core Ivy Bridge CPUs, all illusions vanish into thin air the minute it gets down to power consumption.

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