Comments on: Solar Powered PC

By: etbe

etbe — Fri, 18 Apr 2008 08:28:18 +0000

wjl: If you tested the same machine you would not end up with totally different numbers. The difference between a machine with 1G of RAM and a machine with 4G would probably be lost in the noise, but the difference between a P3 and a P4 (or other similar differences) would be obvious.

vedran: Correct. I’ve updated this post to be based on the system without monitor.

By: Ben Hutchings

Ben Hutchings — Fri, 18 Apr 2008 00:48:54 +0000

Working at a hardware vendor, I know that OEMs are very interested in power requirements. You should find power consumption on data sheets. However, you might have to look at data sheets for individual chips rather than boards.

By: Albert Lash

Albert Lash — Fri, 18 Apr 2008 00:25:34 +0000

You might find this interesting:

http://www.docunext.com/blog/2007/08/16/solar-powered-dectop/

By: vedran

vedran — Thu, 17 Apr 2008 23:10:04 +0000

Just to make a note, their system uses 61W when idle, and yours uses 52W. But they’ve figured the monitor power in the number, and you haven’t.

By: wjl (Wolfgang Lonien)

wjl (Wolfgang Lonien) — Thu, 17 Apr 2008 22:30:28 +0000

The reason *I* don’t publish anything like that on zareason.de is that customers would start measuring with their own devices - and none of these measurements are really comparable.

If I would test the same machine like Tom’s Hardware or the German c’t magazine, I would end up with totally different numbers.

That could cost vendors and consumers more than it would help, at least here in Germoney ;-)

cheers,
wjl

By: etbe

etbe — Thu, 17 Apr 2008 22:15:47 +0000

Joe: I guess it must be leakage. If the system is working correctly (IE the resistance is not great enough to prevent it functioning) then resistance could be expected to decrease power use.

Interesting point about talking to RAM. What we need is a module with CPU, motherboard logic, video, ethernet, and 1G of RAM on the same module. That would be quite achievable, such chips from a P3 class machine (apart from RAM) would probably use less transistors than some of the modern multi-core CPUs.

some guy: I don’t think that superconductivity is relevant to this discussion as it’s not used in CPUs at this time.

By: Joe Buck

Joe Buck — Thu, 17 Apr 2008 21:50:14 +0000

Also, the most power-expensive operation a CPU can do is to drive signals off-chip (mainly to talk to RAM). Cache misses don’t just cost time, they burn power.

By: some guy

some guy — Thu, 17 Apr 2008 21:48:14 +0000

“Why do CPUs take less power when they are cooler?”

Lower temperature == lower electrical resistance. Heard of superconducting?
http://en.wikipedia.org/wiki/Superconductivity

By: Joe Buck

Joe Buck — Thu, 17 Apr 2008 21:47:40 +0000

There are several reasons why CPUs take less powerful when they are cooler. For an idle CPU, the main reason is that leakage current increases with temperature. For an active CPU, the main reason is that resistance increases with temperature (since delay is roughly a linear function of RC, higher temperature can increase the chance that operations can’t complete within the clock cycle, which is why overclockers chill their CPUs, sometimes with liquid N2).

Notice that there’s positive feedback here: if a CPU gets hot, these effects will make it even hotter, until thermal runaway results (modern CPUs will shut themselves off when they get too hot for this reason).