CPU dissipation measurements on Ace's

[redleader]

Looks like someone finally built a system for recording power use in processors electrically:

http://www.goodwin.ee/sulo/Power2.htm

I made myself a modified PSU, where I measure a DC voltage drop across the DC resistance present in smoothing inductors that are already in place in the PSU. I have RC circuits to smooth out all the voltage ripple so I can just measure an DC voltage drop and would not annoy my millivoltmeter with AC components.



I then measured the DC resistance of those inductors by placing various loads on three power rails and measuring the voltage drop across the inductors. Then calculated the resistance based on a known load resistance and measured voltage drop.



After that I measured all the other important bits that would consume current from the rails that interested me most: +12V and +5V. +5V rail was only interesting with K7 boards because my K7 boards consumed the CPU power from +5V rail. In these cases I only had to measure what HDD consumed from +5V rail. As long as I didn’t have PCI cards in the system, nothing else seemed to consume anything really from +5V rails. To single out current going to CPU from a +12V rail, I also had to measure current HDD consumed from +12V rail and also that of all the fans. The fans were different and so I measured all the fans separately whenever I measured the other stuff. Just pulled out the CPU cooler fan to see how much the consumption dropped, then inserted it right back. The fan in a PSU itself I had of course measured beforehand.



After subtracting all this “other stuff” from the currents I measured from PSU rails, I also had to take into account the efficiency of CPU power regulator. I assumed it to be 84% efficient. No, I have no real experimental basis for this, only a lot of reading of a few powerregulator datasheets. I think it is quite a good guess. If the efficiency is actually higher, then my measured results should be corrected upwards slightly, but more so for load power figures.

He goes on to test a few modern processors. What was interesting was the Palomino figures. They're at least as high as most if not all of the Northwood line. Not prescott though.

[bigben2k]

That's not going to account for the motherboards other power usage, outside of the CPU.

[redleader]

Originally Posted by bigben2k

That's not going to account for the motherboards other power usage, outside of the CPU.

Not sure I follow you, but if you mean:

It doesn't account for the dissipation of the board itself, then I think thats the idea.

If you mean it doesn't account for energy fed into the CPU but dissipated elsewhere then the CPU, I don't think thats all that significant. Most signals are in the milliamp range and at 1.5-3v, so they don't carry all that much power. Probably less significant then the differences in load from the CPU itself over time anyway.

[bigben2k]

Actually, I was reffering to the other components on the motherboard, i.e. the chipset.

[nicozeg]

most of other circuits on mobo use the 3.3V rail....

[redleader]

Originally Posted by bigben2k

Actually, I was reffering to the other components on the motherboard, i.e. the chipset.

Oh. Theres actually something on that too:

One interesting thing that somewhat suprised me when testing K8 and P4 boards. P4 chipsets actually consume the least amount of power. VIA chipsets which have two chips besides the integrated northbridge come a very close second, but most surprisingly, Nvidia nForce 3 chipset, with its one sole chip beside the integrated northbridge, actually consumes a whole lot more than all the others. Especially on boards which use linear regulators to feed the northbridge. My own Chaintech VNF3-250 with a low power videocard consumes almost 50% more from the 3.3V rail than Intel branded i865 board with integrated video (which consumed 10W from 3.3V rail using a single 512MB DS stick). MSI branded KM800 board with integrated video came very close to Intel board though (also with a single 512MB DS stick).

So you can get a pretty good idea as well if you were wondering about chipset + RAM consumption. Generally though i find that a bit less interesting since its so low compared to GPU + CPU (both of which we now have numbers for).