Asus A8N32-SLI Deluxe A64-939 Motherboard

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EIGHT PHASE POWER EFFICIENCY

Methodology

As a general rule, a motherboard does not consume a large amount of power, but when it does, it's almost always the voltage regulation module (VRM) that is at fault. It's a simple matter of physics: A high power processor requires a voltage around +1.5V. The PSU supplies only +3.3V, +5V, and +12V. Therefore, the motherboard must convert one of these voltages into a form that the processor can use; it is +12V line that's generally used to supply the processor. These days, almost every motherboards pull this +12V from the AUX12V line — the juice provided via the 2x12V connector.

There are inherent losses in the conversion from +12V to +1.5V. The total power drawn by the motherboard is always higher than the power required by the processor. The excess is lost in the form of heat. The less efficient the conversion, the more heat is produced, and the more power is drawn by the system overall. Motherboards that can do the voltage conversion efficiently run cooler and require less power under load. Typical motherboards tend to be between 65-80% efficient.

Let's put that in perspective. Assume that a processor draws 75 watts under load (a conservative estimate for many of today's processors). A motherboard with a VRM that is 80% efficient will add almost 20 watts of additional heat to the system. A 65% efficient motherboard may add double that amount!

The A8N32-SLI Deluxe has the potential to cut the amount of heat in the system significantly — if it lives up to its claim of being highly efficient. How efficient is "highly efficient"? We just had to find out, so we decided to compare the A8N32-SLI against another highly regarded nForce4 motherboard.

In this comparison, the same components (or components with equivalent power requirements) were installed on both systems, and the total power draw from the AC source was measured. Any differences in power consumption would be attributed to the motherboards alone.

The following components were used for the comparison:

Test tools included:

  • AC power was measured with an Extech Power Analyzer / Data Logger 380803 power meter. This is a new welcome addition to our lab that allows more precise, unmanned, long term AC power monitoring.
  • Processor voltage was monitored using SpeedFan 4.27
  • Processor specifics were documented using the incredibly useful utility A64 TCaseMax v1.18 by Arthur Liberman, who runs the web site www.thecoolest.zerobrains.com. Please see the sidebar for more details. A screen capture of the result details the processor specifics:

What the above tells us is that this is a fairly cool running processor. A TDP of 65.6W is pretty good for a dual-core processor of this caliber. It also tells us that this is the maximum power the processor will draw under full load with the Vcore at 1.35V.

SIDEBAR: AMD64 TCaseMax v1.18
Text as posted by Arthur Liberman in the www.thecoolest.zerobrains.com/forums

"This is a new type of program, which checks AMD64 CPUs for their maximum rated case temp or TCaseMax and reports the TDP which corresponds to the processor in question.

"On most AMD processors TCaseMax and TDP values are constant, and depend on CPU type and model, but on the E Revision chips, both this value and the default voltage are variable.These are the chips that have variable values:

  • Athlon64 (Venice, San Diego)
  • Athlon64 FX (San Diego)
  • Athlon64 X2 (Manchester, Toledo)
  • All Rev E Opterons and Dual Core Opterons

"What this all means is this: On 90nm manufacturing process, the power leakage of transistors on individual processors differs greatly, this is why AMD implemented TCaseMax. Each CPU has a different TDP rating, here's how it works:

"A program reads the TCaseMax value off the CPU, then depending on the processor (CPU type like A64, Opteron;CPU Rating like 3500+, 146) it finds the processor's Thermal Profile (If you download the "AMD Opteron™ Processor Power and Thermal Data Sheet" and look at pages 10-11 you'll see the different thermal profiles). When the thermal profile is determined, the program finds the TDP rating that corresponds to the CPU's TCaseMax value.

"So in a few words, the higher the TCaseMax, the higher the TDP of a processor will be (the transistor leakage is higher), so the processor will run hotter. Several people have reported that the Opterons rated at 71C TCaseMax were pretty hot. On the other side these processors will be able to reach higher clock speeds.

"That is why we see that on average processors with higher TCaseMax can usually reach higher CPU speeds when overclocked."

The ASUS A8N32-SLI Deluxe was compared against a DFI LanParty NF4 Ultra D. The motherboards were tested in three states:

  • Idle, with Cool 'n' Quiet
  • Idle, without Cool 'n' Quiet
  • Under load, running two simultaneous instances of CPUBurn

Now, here's where it gets hairy: The A8N32-SLI Deluxe does not run the processor at its stock voltage of 1.35V. Out of the box, it was running slightly high, at 1.39V. This slight difference is enough to bias the test results, so the processor voltage was adjusted down manually by 0.0375V, resulting in a final voltage of ~1.36V — close enough. But, there's a catch. The voltage cannot be manually adjusted while Cool 'n' Quiet is enabled, which meant that the Cool 'n' Quiet test could not be completed. In the end we tested it with the Vcore at default.

Test Results

EFFICIENCY COMPARISON: TEST RESULTS
Processor State
ASUS A8N32-SLI Deluxe
DFI LanParty NF4 Ultra D
Idle (CnQ)
116W*
97W
Idle (No CnQ)
141W
105W
Load (2xCPUBurn)
176W
159W
*Processor Voltage for this test was 0.04V higher than stock

Surprised? We sure were! We were so surprised that we re-ran the test a couple more times — and got the same result.

The absolute numbers are not in question — only their meaning. The smallest difference between the two boards was 17 watts, at full CPU load. That is a significant amount of heat. In idle, where most systems spend the majority of their time, the difference was 36W, more than double that. Mind you, most people will run CnQ, and the difference then drops to 19W.

The results of this test raised more questions that it answered. How could the ASUS board, with its eight-phase power circuitry, draw so much more power under the same conditions than the DFI board? This question forced us to go back and reexamine our methodology. No conclusions could be drawn, but a few things seemed clear:

  1. A higher total power draw doesn't necessarily mean that the motherboard is less efficient. The 36 watt difference between the two motherboards at idle is far too much to attribute to differences in motherboard VRM efficiency alone.
  2. The two motherboards do not have identical chipsets.

One other item that was examined was the power testing results for the Asus A8N-SLI Premium board that was used in a PC built for an old friend of Mike Chin in Thailand. A different PSU was used, but its efficiency is slightly lower than the one used here; most other components were reasonably close: The same model processor, a single HDD, a gig of RAM, and a slightly less power hungry video card, the 6800GS. Here are the results, from the table on page six of that article.

Asus A8N-SLI Premium (Thailand system)
Processor State
Total AC Power
Idle (CnQ)
94W
Idle (No CnQ)
99W
CPUBurn, Prime95 and 3DMark05 simultaneously
190W

The maximum power draw of 190W can be discarded because it was a peak measured while the system was under higher load than the other two boards tested here. However, the idle power measurements are much closer to those of the DFI LanParty NF4 Ultra D board than the Asus A8N32-SLI Deluxe. Why?



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