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Looking at system power consumption is interesting to a certain degree, however, for all practical purposes we are more interested in the isolated CPU power consumption. To estimate the latter, we used the same power measurement setup as in previous reports. Briefly, we used a Fluke 80i-410 AC/DC current probe in combination with a Wavetek Meterman 30XR multimeter to measure current through the isolated +12V supply lines feeding into the CPU VRM. To increase granularity of the measurements, we ran the supply lines in a triple loop through the clamp. The clamp itself was calibrated using a BK Precision model 1692, 30V 40 A DC power supply. Since there is a temperature dependency of the probe, we monitored the zero-current offset at the beginning of each measurement as well as at the end of each run. If the values drifted we retook the measurements. Despite these precautions there are possible deviations of the read-out from the real current, however, these errors mostly affect the lower (processor idle) measurements. We estimate that the errors should not be more than 10% at the lower end of the data and less than 5% in the mid and higher data range. Moreover, since the same procedures were applied to all processors tested, there may be an offset in the absolute numbers, however, the relation of the individual cores to each other with respect to power consumption should be fairly accurate. The extremely high power consumption of the CPU at full load causes a voltage droop by approximately 500 mV on the 12V output, the calculations are corrected accordingly.
In addition to the method outlined above, we used a modified PSU to run the 12V line directly through the Wavetek Meterman and read out the current. Both methods gave identical results.
Lostcircuits CPU power measurements appear to be very consistent too when you look at FX60, FX62, E6700 and QX6700. FX60 consumes 81W, FX62 consumes 100W and 2x FX74 consumes 266W under XP32. Scaling linearly from FX60 to FX62 we should expect a single FX74 to consume a minimum of 119W x 2 = 238W. However, since we all know that 3Ghz is very close to the limit for K8, we should expect to see power consumption rise exponentially with clock speed when approaching the core's limits. E6700 consumes 54W so logically QX6700 should consume a minimum of 108W and we all know that 2.66GHz is not even close to the limits of 65nm C2Q. It's hardly a perfect testing methodology but I've yet to see any better.