Question about CPU power usage

chamrog

February 9, 2007 11:49:30 AM

Im looking to buy a new pc that is going to run around the clock, so i was wondering how i how much i could save on my powerbill choosing a cpu that runs at a lower voltage.

Athlon 64 X2 3600+ 1.9 GHz 1.25V/1.35V 87 EUR

Athlon 64 X2 3600+ 2.0 GHz 1.2V/1.25V 113 EUR

Athlon 64 x2 3800+ 2.0 GHZ 1.025V/1.075V 346 EUR

So my question is will i save anything in the over a few years choosing, a procssor that runs at a lower voltage, or does it all get eaten up by the price of the processor .
The price for electricity where i live is 0.22 EUR per KiloWatt Hour

Any one that has any feed back for me :?:

Knudsen|DK|

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CaptRobertApril

February 9, 2007 1:04:51 PM

Quote:

Im looking to buy a new pc that is going to run around the clock, so i was wondering how i how much i could save on my powerbill choosing a cpu that runs at a lower voltage.

Athlon 64 X2 3600+ 1.9 GHz 1.25V/1.35V 87 EUR

Athlon 64 X2 3600+ 2.0 GHz 1.2V/1.25V 113 EUR

Athlon 64 x2 3800+ 2.0 GHZ 1.025V/1.075V 346 EUR

So my question is will i save anything in the over a few years choosing, a procssor that runs at a lower voltage, or does it all get eaten up by the price of the processor .
The price for electricity where i live is 0.22 EUR per KiloWatt Hour

Any one that has any feed back for me :?:

Knudsen|DK|

Calculation is very simple.

1) Choose the W rating of your processors, let's say you are comparing a 85W vs. a 125W. So the difference is 40W.

2) Multiply that by the number of hours it will be on every day. If it's gonna be on constantly, then that is 24.

3) Multiply that by 365 to get the yearly kilowattage.

4) Multiply that by the cost of electricity in your area.

So if you were gonna compare those two processors for your own factors, your formula would be:

.04 x 24 x 365 x .22 = 77.01 Euros per year.

Now that would be 77 Euros if you were folding the CPU 24/7. Under realistic use your actual electric usage would be a mere fraction of that.

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WR

February 9, 2007 4:49:16 PM

At a glance it seems the 113 EUR chip is most efficient for you.

AMD specifies Thermal Design Power (TDP) for each of their CPUs. Those are maximum wattage figures, and actual usage even at 100% load is substantially lower. However, if you plan to load your CPUs fully, you should use that TDP difference directly in your energy calculations. That's because your power supply isn't 100% efficient (actual range 70-85%), and so your CPU power requirements understate actual socket draw. It is more important for energy conservation that you focus first on a power supply with 80%+ efficiency rather than pick between similar models of a CPU.

Also, if you're running at 100% load full-time, you should adjust the voltage/frequency settings in BIOS. Your aim would be to decide the lowest acceptable frequency and find the minimal voltage to keep that CPU stable. Performance-per-watt is inversely proportional to the square of voltage, and in general more expensive CPUs can reach lower stable voltages for a given frequency.

If you're not running at full load, then you'll have to settle for the default voltages. Power saving technology on AMD CPUs is pretty strong such that you needn't worry so much about small TDP differences - again, focus on the power supply efficiency in the 20-50% load range.

P.S. One watt running continuously would drain 17.5 KwH over two years and cost 3.86 EUR at that rate... that's pretty expensive over there heh.

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