Many years ago, I set up a Web server using a spare 486DX2 tower machine and Linux. The experiment was to test Linux, and also start serving some very basic HTML from a dial-up Internet connection. The system worked beautifully — too well, in fact. It was supposed to be a demonstration, but turned into a working mail and Web server for a small company. When the machine was finally taken out of service, I removed the case and found that the tiny CPU fan had fallen off and the processor was running “naked” (my dust forensics told me it was like this for quite a while). When your processor is putting out a maximum of 7 watts, you can live with such failures. As anyone can tell you, a fan failure is not tolerable in today’s servers where the heat output is more than ten times what it was in my little Web server. Heat has become a major problem.
As vendors strive for faster processors and denser systems, power and cooling has become a major issue for the HPC market. For system designers, the rule of thumb is that a 10 degree Celsius rise in temperature produces a 50% reduction in the long-term reliability of electronic hardware. Reliability in today’s servers depends on how well you can move heat with air (I am going to ignore liquid cooling methods for now). Thermodynamics tells us that in a closed system we can only move heat and that…
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