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.'"

Comments

Underclocking makes sense to me

[Dolphinzilla]

If you are designing a system for high reliability, under temperature extremes and such (military environments for example) underclocking is the way to go - you can minimize power and heat loads as well as potentially avoid timing instabilites that occur when you push a processor to the performance margins.

Re:Underclocking makes sense to me

[ignorant_coward]

For high reliability, I'd just buy a pre-engineered system from IBM or Sun rather than put on my engineering hat and pretend I know what I am doing.

For hobbyists, all this is good and fun, but I'd hate for my anectdotal experience of one machine running underclocked well to be the underpinnings of a business webserver.

Their Maths is a little suspect in places

[kabbor]

They listed the drop in temperature from 33.5 to 26.9 as a 20% drop. However, they didn't mention the ambient temperature. If you take 20 degrees, then this drop is more like 50%. That would also mean that it was consuming well under half the power. (I'm assuming watts->degrees is exponential.)

As a secondary matter, the person who got me interested in BSD, as a rule, made his servers with whatever was the cheapest AMD-K6, underclocked to 350MHZ. Bulletproof boxes with long lifetimes. I'm sure there are still some churning out the bits around this town.

Faulty Analysis?

[Brian Blessed]

The temperature measurements in the article don't seem to be relative, and yet they say things like this:

for a 66% drop in speed there was a 20% drop in temperature.

In this context, talking about a 20% drop in temperature in degrees celsius makes no sense for comparison purposes. They go on to state that "a 43% drop in voltage producing a 20% drop in heat seems more reasonable", but this is assuming that the temperature drop corresponds to a equal reduction in heat output.

- Brian.

Re:Don't keep us in suspense

[pla]

a very fast, very hot modern processor (in this case an AMD Athlon 64 4000+)

Very hot? If you haven't already bought one, just make sure to get one with a Winchester or Venus core.

Using C&Q, mine (only a 3000, but "close enough" to make my point) could probably get away with purely passive cooling. Using a meter at the plug, it draws a whopping 54 watts average, with 48W idle (C&Q engaged) and 65W max.

Thanks to modern CPU power saving technologies as implemented in all newer Athlons and Opterons, or Pentium M, you really don't need to sacrifice peak performance for the sake of power and heat. They deal with usually sitting there idle fairly well, by throttling back, without needing to resort to such (relatively) drastic measures as "suspend" and "hibernate".


I do, however, see one possible use for underclocking... When you keep your CPU always pegged at 100% (running Seti @home or the like, for example). Then, underclocking would allow you to trade a little bit of performance for a lot of power and heat reduction.