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AMD Athlon64 4000+ Underclocking
Bios_Hakr writes "PC Stats is running an article on their experiences underclocking an AMD 4000+ processor. Their goal was to try and reduce the voltage requirements and lower the heat output. They benchmark using 3dMark01, 3dMark05, as well as SuperPi. From the article: 'This got us thinking though; what about under-clocking? Most modern processors and motherboards can just as easily run under a rated speed as it can run over... but is there a point to this? Well possibly.'"
I have an Athlon 2100+ which I bought back in 2002 when it was brand new. After installing it, I experienced frequent lockups as the CPU overheated under heavy loads. I bought a new heatsink/fan combo (a Thermaltake Volcano 9, which was pretty good at the time) to replace the standard AMD one, but it sounded like a jet turbine at full speed and it only alleviated the problem a little. After that, I underclocked my FSB by only 3MHz (133MHz to 130MHz) and I haven't had a lockup in over a year. The associated drop in performance is unnoticable.
OLPC Australia
Actually, the parent poster is more insightful than the mods have thought (modded +4 Funny right now). There actually are engine control systems for motors with more than 4 cylinders that automatically turn off a few cylinders when running at low load. That moves the working point for the remaining cylinders to a more economical point (ie running at very low load is very inefficient), saving fuel (but not as much as when choosing a smaller motor - but maybe you just need the power sometimes etc).
I have a really elegant proof for Fermat's last theorem. If this sig was only a bit longer...
Use CrystalCPUID to manage your AMD64 CPU's speed and voltage rather than the default Cool 'n Quiet power management (set your Power Scheme to "Always On" to disable that, definitely leave the CnQ driver installed). On most HP AMD64 notebooks we've found that you can usually safely set the core voltage at about 0.2V below stock at full speed. Judging by the AMD Thermal Design Guide, that's enough to cut power consumption nearly in half. I swapped in a Mobile-class Athlon 64 3200+ into my Pavillion zv5000z in place of the stock DTR-class chip and have been running 1GHz at 0.8V, 1.6GHz at 1.025V, and 2GHz at 1.225V for months. That puts the full speed power consumption at slightly above AMD Turion ML levels. For the stock DTR chips, 1.3V at full speed is popular.
Of course, in average use, the standard AMD Cool 'n Quiet behavior of running 800MHz at 0.95V while idle will give you battery life that's almost as good as an undervolted setup. 3-4 hours of battery life with a 12 cell battery is common, versus a fraction of that for the poor bastards who bought the P4-based zv5000 series (HP wisely dropped Intel CPUs from their zv6000 line). Undervolting does wonders under heavy CPU load though.
MobileMeter is my favorite way to monitor CPU speed and temperature, and Hot CPU Tester Pro verifies that I didn't go too far.
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The article states:
Unless the computer and participants were in a frozen room (at 0 degrees celcius), their analogy is flawed. The amount of heat generated is directly preportional to the temperature INCREASE above the ambient temperature. Let's assume that the test occurred at "room temperature" (70F deg or 21C deg). The chart would look more like the one below:The article should have stated:
"For a 66% drop in speed, there was a 53% drop in added temperature."
"a 43% drop in voltage produced a 53% drop in in heat seems more reasonable."
My observation from that data above:
"A drop of only 400MHz (17%) and 0.15V (11%) showed a significant drop in the amount of heat generated (25%)."