Pushing The Best To The Wall

SUMMARY: You can huff, you can puff, but you can’t make a silk purse out of a sow’s ear.

I thought it would be interesting to graphically show what the heatsink manufacturers are up against as they try to meet Socket A cooling requirements.

I took four representative, fairly good heatsinks that are recently on the market and tested them using three fans: YS Tech @ 26 cfm, Delta @ 38 cfm, and my “Extreme” at 90 cfm. I used the ABIT KT7 running a Duron 800 @ 1000, 1.9 volts, 52.6 watts, and found the following pattern:


Alpha PEP66, Global Win WBK38, Taisol CGK742092 and Vantec FCE62540D.

Interpreting C/W: For every watt the CPU radiates, the heatsink will cool the core by the (C/W x watts) plus ambient temp. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU temp will be 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

What you see is that all these heatsinks, for all their “different” designs, all start to converge at a point: C/W of 0.2. And THAT using a 90 cfm fan that is intolerable! Now, let’s say you have an overclocked T-Bird at 1400 MHz, 1.9 volts, radiating 85 watts of heat.

What this means is that, right now, about the best you can expect with your system temp at 25C is to keep that T-Bird at about 42C (0.2 C/W x 85 watts = 17C; 25C + 17C = 42C). For a lot of folks, 25C is room temperature, so if your case temp is 35C add another 10C: 52C for the T-Bird’s temp. A C/W of 0.3 puts you into some scary territory: a 35C case temp gets you over 60C.

It’s been my experience that at about the mid 40s and up, CPU stability starts to decrease, so with what’s out there now, we’re starting to see a “compression” between overclocking speeds and air cooled heatsink performance. As AMD pumps out 1.2 GHz+ CPUs, this “compression” really starts to come into play. By the end of the year, I don’t doubt that overclocked CPU heat of 100 watts will be commonplace.

Barring water cooling (still my favorite) or peltiers, the challenge heatsink manufacturers face is daunting; adding hot fans to yesterday’s heatsinks is not going to cut it. Maybe some of you can live with a Delta 38 screaming at you, but most can not. He who innovates, wins.

The challenge overclockers face is as daunting; for instance, taming and disposing of 100 watts is going to require a lot more attention to case cooling and system air flow. Expect to see more ducts, blow holes, 120mm intake and exhaust fans, just to mention a few items.

Something has to give. AMD is coming out with new CPU designs that will run cooler, but 70 to 100 watts will be the overclocking “norm” with AMD’s CPUs for the next 6-12 months.

Email Joe

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