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Message 10363 - Posted: 1 Jun 2009 | 18:32:04 UTC

I had a phenom 9750 in my system, 4GB RAM and 1TB Drive, but only an 8600 graphics card - that took days to finish a task, and rarely did! I mainly ran other Boinc Projects, mostly WCG.

When using the system I liked to keep the CPU under clocked, as it did get a little noisy. The system used around 200W normally and about 167W when under clocked.

I replaced the CPU with a Phenom II 940 and the GPU with an 8800GT.

As the new core can drop its frequency all the way down to 800MHz (using only 0.992 V) this makes up for the more demanding video cards energy requirements. So when I turn the voltage down (just under vista’s Power Options, in control panel) the system still uses 167W, despite the hungrier GPU, and native CPU. Should I want the extra CPU speed for a while, I can pop it back up to 3GHz, and it will eat up another 110W.

Essentially, I did this because I do Boinc projects, and I think GPU crunching is more energy efficient - in terms of crunching productivity per Watt.

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Message 10497 - Posted: 12 Jun 2009 | 19:30:15 UTC - in response to Message 10363.

I think GPU crunching is more energy efficient - in terms of crunching productivity per Watt.


If the GPU is used properly this is indeed true.. and the reason why I'm pleased to be able to run GPU-Grid :)

However, the GPU can not run all algorithms efficiently. In fact, there are rather few which run OK on current GPUs.. so we'll still need the CPUs for quite some time.

If I were you and wanted to maximize energy efficiency I'd leave the CPU at the minimum voltage and clock it up as far as possible. I'd guess that's just shy of 2.0 GHz. Doubling the frequency doubles the power draw of the CPU, but there's a certain amount of power which you always "waste" just by running the PC, regardless of CPU speed and load. That's the HDD, optical drives, cards and to some extent the motherboard chipset and RAM. due to this "offset" to power draw a doubled CPU power draw will not double your total power, and thus you're actually more power efficient at 2GHz @ 0.9V than at 0.8GHz @ 0.9V.

Being strict could probably mean that in total you'd even be more efficient at 3 GHz at reduced voltage (or any other value in between those).. but I agree with you, running the cpu at the smallest voltage possible is kind of nice :)

Oh, to set these: either ask your bios or try "K10Stat".

MrS
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Message boards : Number crunching : Watt a crunchy GPU

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