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Overclocking

System Builder Marathon, Dec. 2011: $2400 Performance PC
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The motherboard of our previous $2000 build became unstable after prolonged heavy use when overclocked. Relatively low CPU temperatures tend to indicate a voltage regulator that has been pushed beyond its optimal thermal range. The previous build was able to maintain stable voltage up to the point where it got hot, crossing its thermal threshold at around 1.35 V with our Core i7-2600K CPU maxed out.

The problem was that our CPU needed a little more voltage to get a decent overclock, and we couldn't give it anything more without asking too much from the platform.

MSI’s Z68A-GD55 lost our motherboard comparison partly because its voltage regulator was always saggy. And yet, the same board had superior voltage regulator cooling. The practical impact of switching to this board was that we needed to set 1.40 V to approach our target 1.38 V, but we got there without encountering heat issues. Mission accomplished.

Our memory is known to overclock past DDR3-1866. Unfortunately, its default timings wouldn’t permit that setting on MSI's Z68A-GD55. The board didn’t automatically loosen timings when we specified higher data rates in the same way as many competing products, and manually choosing higher latencies still wouldn't permit DDR3-1866 operation. To get a slight boost in memory bandwidth, we chose 45 x 102.2 MHz, rather than 46 x 100 MHz, to reach a CPU clock of 4.6 GHz.

With our memory only 2.2% above stock, we were instead forced to optimize latencies for added performance in the system’s overclocked state.

Even at the board’s 1.40 V setting, voltage dropped to 1.368 V when the overclocked CPU was loaded with eight threads of Prime95.

A combination of higher-grade chips and better cooling allowed our GeForce GTX 580s to overclock eagerly, even though we didn’t touch their voltage levels.

Take this warning to heart: PNY’s liquid-cooled cards should only be used with custom fan speeds, even when they're not overclocked. That’s because the memory and voltage regulator are still fan-cooled, and the fan is controlled by GPU temperature. Our tests indicate that PNY doesn't alter the air-cooled-card’s fan profile, and the lower GPU temperatures enabled by liquid cooling result in the fan slowing down to a point that the card can overheat.

An ideal solution would be to move the thermal sensor that controls the fan to the card’s voltage regulator. However, the reference GeForce GTX 580s that PNY uses aren't designed to allow this. Instead, we used MSI Afterburner to set a custom fan profile keyed to the moderate temperatures these liquid-cooled GPUs experience under stress. Afterburner must be running for its fan controls to work, so we set the “Start with Windows” and “Start minimized” options under its Properties menu.

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