EPU Testing:
In this portion of the review, the ASUS P5E64 WS Evolution motherboard was run through a series of tests in order to monitor not only performance data, but also electrical data. There are five profiles available in AI Gears, and three were chosen to see just how EPU might impact system performance. Maximum power savings, high performance, and turbo modes were chosen, since auto mode wouldn't provide results that were particularly unique, and medium power saving mode wound up being very similar to high performance mode in preliminary testing.
The first thing to consider is the different performance profiles associated with the three modes of operation:
» Maximum Power Savings - 1800MHz CPU (6x 300MHz FSB), 1200MHz memory
» High Performance - 3000MHz CPU (9x 333MHz FSB), 1333MHz memory
» Turbo - 3150MHz CPU (9x 350MHz FSB), 1400MHz memory
Basically, maximum power savings mode is an extreme underclock, high performance mode is the same as stock settings, and turbo mode is a slight overclock (about 5%). None of these profiles allow you to get too crazy with overclocking, and all of the benchmarks shown previously were run at speeds even higher than turbo mode.
The chart below combines data taken from a few sources in order to establish a baseline reading on the electrical properties of these three modes of operation.
The CPU voltage value was recorded from the main screen of AI Suite, and could be confirmed from other system diagnostic utilities. What we see is that the maximum power savings mode offers a 10.6% reduction in voltage over the other two modes. Even more interesting is that even in high performance or turbo modes, the CPU voltage is about 0.2V less than I would apply otherwise. If I was manually setting the CPU voltage it would be just above 1.3V, but with EPU it will apply that voltage only if necessary.
The CPU wattage value was recorded from the tool tip provided in the Window's taskbar. This value would fluctuate a bit upon each check, and the modal value of a dozen samples was chosen. What it shows is that the maximum power savings mode really does have a high percentage impact on CPU power consumption... almost 75% in this test! The problem is that CPU power is such a small portion of overall system power, that the net benefit is almost trivial.
The final bit of data from the chart above is for total (system) wattage, as monitored with a Seasonic Power Angel. This confirms that despite the 75% power savings on the CPU, the total power savings from your electrical outlet is just 4 watts, or 3.6%. Something small is better than nothing, but it is hard to get excited about it.
The next test involved running OCCT for a 30 minute session while stressing the processor and memory. OCCT was used to monitor the CPU voltage, while the Power Angel was used to monitor the total power being drawn from the wall. The screenshots below summarize the results from OCCT for each of the three modes of operation, and from left to right we have maximum power savings, high performance, and turbo.
  
What we see here, and confirmed looking back at the idle load testing results, is that the voltage actually drops under load in maximum power savings mode. In high performance and turbo mode the voltage now climbs to about where I would have set it if I had configured the system manually. In terms of total power consumption, maximum power savings mode sees a rise of 20 watts (17.9%), while high performance mode and turbo mode rose 43.1% and 49.1%, respectively.
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