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AMD's Bulldozer Architecture: Overclocking Efficiency Explored

Overclocking And Efficiency Are Like Oil And Water With Bulldozer

Overclocking does pay off when you're overclocking AMD's FX-series processors, but only when your goal is to achieve maximum performance. In our test, we can overclock fairly easily using liquid or aftermarket air cooling. If you just don’t care about power consumption, you can crank up the voltage and see clocks that exceed 4.5 GHz on across all four Bulldozer modules. But if energy is expensive where you live and you also care about efficiency, performance considerations are less important. The same overclocking exercise results in a very detrimental increase in power consumption.

When you use all of your self control and refrain from touching any of AMD's settings (clock rate, voltage, and so on), the FX-8150 runs more efficiently than any overclocked setting we tried, achieving an efficiency score of 288 points. When you drop the CPU voltage, there's a small performance increase, perhaps explained by a reduction in thermal output and more aggressive application of Turbo Core. The system consumes significantly less power at the same time, though, and thus is our efficiency champion, sporting an efficiency score of 319 points.

However, that's not going to be enough to impress someone with a Sandy Bridge-based platform. FX certainly can't surpass Intel's mainstream effort in that regard. As we've seen, the efficiency scores of Intel's processors begin at 320 and top out at more than 635 points, achieved by Core i5-2500K and Core i7-2600K. Thus, Sandy Bridge and Sandy Bridge-E offer significantly more performance per watt of electrical power than Bulldozer, which is caused primarily by the fact that the Intel processors do not require such extreme voltage increases to realize higher clocks.

During its press briefing, AMD's architects claimed that the decisions they made in putting Bulldozer together were driven by a desire to achieve better efficiency than its aging Stars design. Given the numbers presented today, we're pretty sure something went wrong along the way. At its stock settings, Bulldozer comes close to being competitive, but it's not clear how AMD plans to scale the performance of this design over the next year (before Piledriver is ready) without increasing voltage and actually hurting efficiency in the process.