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James Gorbold

Input/Output - The quad-core challenge

Posted at: 2nd October 2007

Quad-core CPUs are stupidly fast, but they need equally powerful cooling hardware to work at their best.


As I write this article, AMD is announcing the launch of its first quad-core CPUs - the Barcelona core Opteron 23-series. However, while AMD has struggled to get a quad-core CPU out the door in a timely fashion, Intel managed to do it back in November last year, and has already released 22 quad-core CPUs: three Core 2 Extremes, one Core 2 Quad, nine LGA771 Xeons, three LGA775 Xeons and six Xeon MPs.

However, while quad-core CPUs are immensely powerful, they also produce a prodigious amount of waste heat. They have a significantly higher TDP rating than their dual-core equivalents, but simply comparing TDP values is literally only half the story. The other factor to consider when comparing dual- and quad-core CPUs is heat density. As Intel's quad-core CPUs are built in the same LGA771 and LGA775 packaging as that of dual-core CPUs, and therefore have the same size heatspreader, quad-core CPUs have a much higher heat density than dual-core CPUs. This is a major problem, as it's much harder to cool a CPU with a high heat density than a CPU that has a high TDP and low heat density.

As a result, if you're upgrading from dual to a quad-core CPU, or are going straight to quad-core, you need to pay a lot of attention to how you intend to cool your new monster CPU. Gareth and I (the only members of the CPC team to have quad-core rigs at home) have had to upgrade our PCs' cooling hardware more often than the Conservative party elects a new election-losing leader.

Our foray into the world of Core 2 architecture CPUs began with Core 2 Duo E6700 CPUs that were cooled by Arctic Cooling Freezer 7 Pro HSFs. This incredibly low-priced HSF has retained its place on the CPC Elite for more than a year, as it remains the most cost effective way to cool a dual-core CPU. After that, we upgraded to quad-core CPUs; Gareth chose a QX6700, which he overclocked from 2.66GHz to 3GHz, and I opted for a Q6600, which I overclocked from 2.4GHz to 3GHz. After a few short weeks, it quickly became apparent that while the Freezer 7 Pros could cope with the heat output of these quad-core CPUs, our ears couldn't handle the noise of the Freezer 7 Pro's PWM-controlled fan, which adjusts its speed according to the temperature of the CPU. When mounted on the dual-core CPUs, the fan spins comparatively slowly, so it's very quiet, only occasionally spinning up to full speed. In contrast, when mounted on the overclocked quad-core CPUs, the PWM fans spent almost all day at full speed, and as a result, were rather loud.

As neither Gareth nor myself are big fans of noisy PCs, we decided that some form of more powerful and quieter CPU cooling was in order. Gareth's next move was to try to water-cool his overclocked QX6700 using a mix of different components from a variety of manufacturers including Corsair, Swiftech and Zalman. Unfortunately, this venture ended in tears a week later when the bolts securing the waterblock to the CPU snapped; this not only caused the CPU to overheat and shut down, but also killed the motherboard, as a shard of metal cut one of the traces on the surface of the PCB. Gareth's third and (so far) final attempt to cool his overclocked QX6700 - after buying a new motherboard - was to fit a Tuniq Tower 120. This mammoth HSF is so large that it won't fit on many motherboards, but it has a manually speed-adjustable fan, and was capable of cooling the overclocked QX6700 while also remaining quiet.

For my own sins, I decided to stick with air cooling a little longer, trying out a series of progressively larger HSFs. First, I fitted a more powerful fan to the Freezer 7 Pro, but this barely improved its cooling ability. I then decided to confront the Scythe Infinity with the quad-core challenge. However, while this monster HSF initially proved to be superior to the Freezer 7 Pro, once I'd upgraded to a QX6850 (which I also overclocked), the CPU temperature was far too hot for comfort (95˚C under load), even after I modded it with a huge 38mm deep SilenX fan. The next CPU cooler to attempt the quad-core challenge was a Titan Amanda TTC-NP04TZ. This innovative HSF uses a lower-power TEC to move heat from the CPU into the nest of fins above it, but even this hybrid design was unable to pass the quad-core challenge, with the two 92mm fans setting off an irritating vibration that was transmitted through the rest of the case.

My fourth, and to date final, attempt to keep my overclocked quad-core CPU in check was to employ the cooling powers of a Swiftech H2O-Apex Ultra. In just over nine months of experimentation, this high-end water-cooling kit, which uses 7/16in ID tubing and a dual 120mm-fan radiator, was the first device that was able to keep an overclocked quad-core CPU cool and quiet. With the radiator's two 120mm fans tamed by a pair of Zalman FanMate fan controllers, and the MCP655 pump set to speed mode two (out of five), the kit proved to be whisper-quiet, and kept the CPU under 60˚C at full load. The only problem is that assembly took a whole weekend, and necessitated rebuilding my PC inside a new case, a SilverStone TJ07. This required some modding to fit the dual 120mm-fan radiator inside, but that's another story for another day.

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