Jul 8 2007 8:12PM | Permalink | Email this | Comments (1) |
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Computer CPUs are energy hogs because virtually all power dumped into chips for computation is eventually converted to heat.

The International Technology Roadmap for Semiconductors (ITRS) outlines hurdles chip manufacturers face as they decrease component size to keep pace with Moore’s Law. While these barriers address the fundamental physics of nano-lithography processes, the computer industry’s genius at bending the laws of physics to further miniaturization is being up-staged by a more primitive problem – heat. As CPU components are shrunk, chip power density increases, and cooling becomes more difficult. In fact, the fundamental barrier to increased computational density may not be lithography limitations but inability to provide adequate chip cooling.

In a white paper on computer server rooms, “Fundamental Principles of Air Conditioners for Information Technology,” Tony Evans estimates that a single blade server chassis can release 4 kW of heat energy into its IT room, and for each 1000 watts drawn by a computer server, at least 350 additional watts are needed to run the air conditioning system.

Poking fun at this very serious problem, some folks have demonstrated frying eggs on computer CPUs. For example, “Office Snack” shows a cubicle junky cooking lunch on his CPU while “How to fry an egg on an XP !!” gives step-by-step instructions on an 11-minute over-easy egg.

A bit more unsettling are the over-clockers who still have not learned the difference between temperature and heat. One over-clocker asks “can I cool a CPU with dry ice?”, and my personal favorite is the guy who ultra-over-clocked his CPU with liquid nitrogen. Just because a substance is cold does not mean it provides good cooling! Please look up the heat transfer coefficient and the specific/latent heat of your coolant before you try this at home!

The best approach to CPU heat mitigation is to consider cooling as the primary design parameter. I suggest going so far as to place thermal management above processor speed, a philosophy adopted by VIA Technologies, Inc., which produces very energy-efficient, cool-running processors.

Another approach to cooler-running CPUs (which I dislike) is to take a chip not optimized for thermal management and administer its power utilization with software. Intel has adopted this approach, as highlighted in “Power Plays: How power consumption will shape the future of computing”.

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