Ted Samson writes "In their latest round of energy-efficiency tests between AMD Opteron and Intel Xeon, independent testing firm Neal Nelson and Associates find AMD still holds an edge, but it's certainly not cut-and-dried. Nelson put similarly equipped servers through another gauntlet of tests, swapping in different amounts of memory and varying transaction loads. In the end, he found that the more memory he installed on the servers, the better the Opteron performed compared to the Xeon. Additionally, at maximum throughput, the Intel system fared better, power-efficiency-wise, by 5.0 to 5.5 percent for calculation intensive workloads. For disk I/O intensive workloads, AMD delivered better power efficiency by 18.4 to 18.6 percent. And in idle states — that is, when servers were waiting for their next work load — AMD consistently creamed Intel."