I was very surprised that ASUS pays so much attention to their new ASUS EPU power-saving technology in general and ASUS P5N-D mainboard in particular. Even the marketing slogan for this board says: “The best platform combining powerful performance with great energy efficiency". ASUS EPU (Energy Processing Unit) technology is mentioned on both sides of the mainboard package, in the brief list of specifications and in the detailed spec sheet on the company web-site. This technology allows changing the number of active phases in the processor voltage regulator circuitry depending on the current workload thus saving power. You can even watch a funny video about gardens blooming on our planet thanks to all the saved energy. And when we saw the first results of ASUS P5K-SE with ASUS EPU technology and Gigabyte GA-EP35-DS3L using similar DES (Dynamic Energy Saver) technology and both mainboards kind of failed, the companies responded with indignant press-releases.
ASUS can certainly doubt the credibility of the test results performed by their competitor. There may appear alternative comparisons or it may even get to the next level – a legal level. I personally am not so interested in the outcome of this duel, although I do understand the importance of power-saving technologies and am eager to encourage their promotions and development.
Each of these two competing technologies has its cons and pros. As you remember, Gigabyte DES is more flexible in changing the number of active phases, while ASUS EPU uses a two-step adjustment algorithm. However, DES requires a special utility to be installed and running constantly, because, this technology doesn’t work with an overclocked processor. So, for me any pretty much any other overclocker Gigabyte DES is useless. You can read more about Gigabyte DES in our article called Do We Really Need Intel X48 Express? - Gigabyte GA-X48T-DQ6 Mainboard Review.
We have also discussed ASUS EPU in one of our previous articles, namely Asus P5E Mainboard Review and as far as I remember, we were not very enthusiastic about it either. Of course, this technology does work and does save power, although there was no significant result. They keep stressing the advantages of ASUS EPU technology, while keeping quiet about typical drawbacks of most ASUS mainboards eliminating the power-saving gain.
As you know, power-saving technologies do not work on Intel based ASUS mainboards if the processor core voltage has been increased above the nominal. As a result, if you change the processor voltage during overclocking, any ASUS mainboard will consume more power than a similar mainboard from another manufacturer with Intel power-saving technologies up and running and lowering the voltage and multiplier in idle mode.
That is why it is interesting to compare ASUS EPU against Gigabyte DES only from the marketing prospective. It may also be interesting from a legal standpoint, too, if the fight goes too far. However, mainstream overclockers do not really care about these technologies, even though they were initially targeted for them. That is why I wouldn’t even have thought of checking out the power consumption if it hadn’t been for ASUS’ insistent promotion of EPU’s advantages. For that reason and also since I had three different mainboards on the same chipset, it was very interesting to see how their power consumption rates compare.
For our tests we used Extech Power Analyzer 380803. The device is connected before the PSU, so it detects the power consumption of the entire system without the monitor. It even detects the losses in the PSU. It may be a disadvantage for ASUS EPU efficiency estimates, because it only works for the processor voltage regulator circuitry and any insignificant power savings may simply get lost against the background of the entire system. However, it is power consumption of the entire system and not that of its individual components that matters for us, end-users.
Our testing methodology was very simple. We only replaced the mainboards and CPUs in our system case. We loaded the most optimal BIOS settings, without any additional changes. The only thing we did was disabled the FDD, because there was non in our testbed, and enabled power-saving technologies if they were disabled by default. Once Windows Vista loaded I waited until the system became idle and recorded the power data. We used FPU-test from S&M 1.9.1 utility to measure the system power consumption under heavy workload:
As you can see, the reference mainboard on NVIDIA nForce 750i SLI chipset was the most economical. MSI P7N SLI Platinum and Asus P5N-D mainboards consumed about the same amount of power, but ASUS mainboard still required more. We saw the same with a different processor. For example, here are the results taken with Intel Core 2 Duo E4300 CPU:
CPUs drop their clock frequency multiplier to x6 and their core voltage to 1.1V in idle mode that is why the systems with different processors showed pretty similar power readings in these operational conditions. Although Intel Core 2 Duo E4300 CPU works at only 1.8GHz compared to a 3.0GHz Intel Core 2 Duo E8400, the system equipped with the former processor consumes more power, since its Vcore is higher: 1.325V against 1.225V by E8400.