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| Intel's ExtremeEdition P4 955 A giant leap for Intel (process technology) | |
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(Review by MS, December 27, 2005) |
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AMD Athlon 64 X2-3800+ (Manchester) |
Power Consumption
We used the same power measurement setup as in out previous reports. Briefly, for isolated CPU power measurements, we used a Fluke 80i-410 AC/DC current probe in combination with a Wavetek Meterman 33XR 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 during 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.
Bear in mind that the power measured is the input power going into the VRM rather than the regulated output power at the individual supply phases. However, the current VRMs are operating in the order of approximately 85-90% efficiency in the worst case. This means that the power measurements are slightly inflated across the board by approximately 10%.
Windows Idle
Prime95
We were running up to four instances of Prime95, hard-assigned to the individual logical cores in different combinanations of load on the logical and physical cores. At the same time we were running Panopsys Throttlewatch to monitor the clock speed and any throttling. For easier viewing, we compiled the different conditions into a single image. To make a long story short, we did not see any indication of thermal throttling, the die temperature was 84 centigrades.
Briefly, we ran Prime95 and recorded the processor power consumption at the beginning of the first Lucas Lehmer iteration (cold) and during the 4th iteration at which the CPU had reached thermal equilibrium. Under load, the Presler core's power consumption is roughly equivalent to that of the older i840 XE. Keep in mind that we were using the extra-large heatsink and, as shown above, we did not run into any throttling that would have occurred with the heatsink provided with the kit. This is important since throttling dramatically reduces power consumption and may well account for the reduced power consumption reported for full load conditions elsewhere.
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Pentium 4 820D (dual core) |
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