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.

Er, did they hear about Cool'n'Quiet?

[marat]

I thought what they are testing is the whole point of AMD Cool'n'Quiet technology, but they don't even mention it in the article! Nice try reinventing the bicycle. I'm already underclocking my Athlon 64 right now, thank you.

Not useful information?

[erroneus]

I think it is somewhat useful information. While most people are thinking about how much faster you can process, many of us are looking to reduce the noise of fans blowing. I recall when 800MHz was a fantastic speed... hell, for that matter, 300MHz was pretty nice too depending on how far back you go.

And are we really using all of those cycles? Not really. Right now, a system's performance (IMHO) is largely the responsibility of the quality of RAM, Video and system board stuff. After all, what "feels" fast must be fast. If I've got a slow hard drive, then it's a slow system and if I can accellerate the video, then it's a slow system. What good is 4GHz if you've got a slow everything else... and by the same token, if you've got a fast everything else, a 2GHz processor is probably plenty.

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.

There is a point...

[chihowa]

On all of my personal must-stay-up servers, I get a processor that is too beefy for the task it's to do, then clock it down. It's usually rock solid and runs very cool. In some cases I've been able to get by using only passive cooling and still keeping the processor very cool, making the system solid, cool, and nearly silent.

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.