CPU Heat / Power

[Wp100]

Hi,

Am looking at upgrading my PC with AMD chips being the likely ones.

Around the same price bracket there are several possible contenders like the Athlon2 x2 265 at 65W, the Athlon2 x3 450 at 95W and just a little pricer a Phenom x4 840 95/125w.

My initial choice was the x2 265 as that has a max power use of 65w so would seem suited to my PC which has to be kept on all day with some very low activity 'background' programs.

It would be good to have the more powerful chips but as they use extra cores and have larger maximum power ratings I would assume when running my 'background' programs they would still use proportionally more power than the little 265 65w chip ? - or will they all use about the same power at these lower activity rates ?

 

[Sceadwian]

Power usage should scale approximately with application utilization.

However...

Just as an example, my last electric bill said the price per thousand watt hours was 3.125 cents, even at full utilization from the lowest power to the highest power chips you said was only 60 watts difference.
There are 8,760 hours in a year. So even if your PC was on 24 hour as day the whole time at max utilization, you would save you 16 dollars a year... not even worth considering, especially considering you don't know the rest of the systems power utilization which is going to be very different from just the processor. I wouldn't even look at the wattage used when buying a chip, with one caveat.. That wattage is almost entirely lost as heat, heat is bad for electronics.

 

[Reloadron]

To add a little to Sceadwian's post.

Given your choices (options) if your motherboard supports it I would go with the Phenom x4 840 95/125w processor. At a small cost increase it will afford more processing power should you have the demand. Also as Sceadwian points out, the power consumed by the processor and subsequent heat generated is a direct function of the work being done by the processor. The less work being done the less heat generated. When heat is generated a good HSF assembly will remove the heat from the processor and dump it into the case. Good case cooling and airflow through the case will remove the heat before it can be detrimental to other case components. Even the amount of heat generated isn't that great or as much as people seem to think it should be.

A few years back I did a science experiment on this subject for a computer hardware forum. The remains of that experiment and images can be found here. The computer used was my workstation system with a pair of Intel dual core 3.0 GHz Xeon processors. The case was configured with 4 thermal sensors (calibrated and accurate). Channels 1 & 2 were the case inlet and outlet temperatures respectively and channels 3 & 4 were the PSU inlet and outlet temperatures respectively. For all purposes channel 1 was the ambient room temperature.

The PC ran at CPU idle for about 30 min and the temps were recorded. The PC was then CPU loaded to 100% on both CPUs and allowed to run 30 min before the second temps were taken. That allowed the case to stabilize with a pair of Xeon processors running at 100% CPU usage.

The results are at the bottom of the linked to page. Note the temperature rise was really not that great. Certainly nothing that would be detrimental to other case components. A good HSF with good thermal compound and good case airflow and there will not be a problem. Those Xeons were generating considerably more heat and using more power than a Phenom x4 840 95/125w would ever generate. I would opt for the Phenom and gain the processing power.

Just My Take
Ron