Test notes
Our aim in the following tests is two-fold: to determine how much the conversion to 65nm has affected the energy efficiency of the Athlon 64 X2, and to see how much overclocking headroom these new parts have. We're not really testing performance today, so consider this a down payment on a future CPU comparo that has performance in its scope. For now, if you're wondering about processor performance, I suggest you check out our Core 2 Extreme QX6700 review for a broad-based comparison or our Quad FX review for a more focused look at very high-end solutions.

I have included some results from Core 2 Duo processors in our tests, but they come with a caveat. We're testing the AMD processors with a relatively low-power motherboard, because our other option on Socket AM2, the Asus M2N32-SLI Deluxe, had some problems (innately high power consumption due to dual 16-lane PCIe 16X slots and dual Nvidia core-logic chips, as well as some crashes with Cool'n'Quiet enabled.) I had hoped to test the Intel CPUs with an Asus P965 Express-based motherboard because the P965 was the lowest power consumer in our Core 2 chipset roundup, but I fried that board attempting to update its BIOS. Doh! Instead, I used Intel's D975XBX2 mobo, which is fairly efficient but still has some additional auxiliary chips and expansion slots that our AMD mobo lacks.

Also, you'll see that we've test a 90nm version of the Athlon 64 X2 3800+ labeled "EE SFF" in the table below. That's the Energy Efficient Small Form Factor version of the 3800+ with a 35W power rating, not the 65W Energy Efficient version.

You will see test results for the Core 2 Duo E6400 processor in this article. That processor came to us courtesy of the fine folks at NCIX. Those of you who are in Canada will definitely want to check them out as potential source of PC hardware and related goodies.

Finally, because we're focusing on power testing, I've only included processors for which I have actual samples—no simulated results achieved by underclocking higher speed-grade CPUs. I did underclock the Core 2 Extreme X6800 to E6600 speeds for our one performance test, though.

Our testing methods
Our test systems were configured like so:

Thanks Crucial for providing us with memory for our testing.

Also, all of our test systems were powered by OCZ GameXStream 700W power supply units. Thanks to OCZ for providing these units for our use in testing.

The test systems' Windows desktops were set at 1280x1024 in 32-bit color at an 85Hz screen refresh rate. Vertical refresh sync (vsync) was disabled.

We used the following versions of our test applications:

• CPU-Z 1.38
• Cinebench 9.5 64-bit Edition

The tests and methods we employ are generally publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.