Power Consumption & Overclocking
We have a few final data points we'd like to cover before bringing this article to a close. Throughout all of our benchmarking, we monitored how much power our Intel based test system was consuming using a power meter, and also did a little overclocking. Our goal was to give you all an idea as to how much power each configuration used while idling and running under load. Please keep in mind that we were testing total system power consumption here, not just the power being drawn by the video cards alone.
The move to a "smaller", more advanced manufacturing process usually means higher clock speeds, and lower power requirements. When Intel moved from a 130nm to a 90nm manufacturing process though, their processors based on the Prescott core ran much hotter, and consumed much more power than expected. This time around, as Intel moves to an even more advanced 65nm manufacturing process, the new Presler core performs more in-line with what you'd expect.
While idling, the Pentium Extreme Edition 955 consumed only 7 more watts than the 840XE, even though the 955 is clocked over 200MHz higher and has a faster bus as well. When running with a full load, however, the Pentium Extreme Edition 955 was much more "green". The 955XE actually consumed 35 fewer watts than the 840XE, and only 20 more watts than the single core 3.73GHz Extreme Edition. Clearly, AMD's Athlons are even more power efficient though.
As we usually do anytime a new processor enters the lab, we spent some quality time overclocking the new Pentium Extreme Edition 955 to see what kind of clock speed headroom was left in its tank. Because the Extreme Edition 955 has an unlocked multiplier and Intel's D975XBX "BadAxe" motherboard has the ability to alter the processor's multiplier via the system BIOS, that's how we ended up overclocking the 955XE.
By default, the 955XE's multiplier is set to 13 with a 266MHz quad-pumped front side bus (effective speed of 1066MHz). So, to overclock the CPU without affecting any other system clocks, we bumped up our processors core voltage to 1.45v and raised the multiplier until the test system was no longer stable.
Initially, we thought we had one monster of an overclocker on our hands as our test system had no trouble booting into Windows with an effective core clock speed of over 4.5GHz. Performance was terrible at this clock speed, however, because the processor was running so hot it would immediately begin throttling. We should note that all overclocking was done with the stock CPU cooler, so this clock speed could potentially have been stable had we used more exotic cooling. By setting the multiplier to 16 and leaving the FSB at its default frequency though, we had no trouble overclocking the Pentium Extreme Edition 955 to over 4.2GHz, an impressive increase of about 800MHz.
Overclocking the processor this high meant much higher temperatures and increased power consumption, however. While idling at this clock speed, our test system consumed 227 watts of power and while running under a full load that number jumped to 334 watts. Unfortunately, we don't have terribly accurate overclocked temperatures to report though, because Intel's Desktop Control Center software wasn't compatible with the motherboard we used for testing. We did immediately reset the system and enter the hardware monitoring section of the BIOS for a few tests and saw temperatures ranging from the mid 70s to mid 80s Celsius.