AMD vs. Intel: power efficiency in the server room rests on RAM
 

Very generally speaking, all three reports found that, when idle, Opteron-based systems tend to consume around 40 percent less power than similarly equipped Woodcrest-based systems. When transaction processing and database workloads are run on the systems, the power gap between the two platforms steadily decreases as the load increases. Under very high load conditions, the Xeon-based systems were able to pull ahead in a few benchmarks.<br><br>

On my reading of these results, what's happening seems to be pretty straightforward. It all comes down to the fact that Intel uses FB-DIMMs and the Opteron uses vanilla DDR2. Simply put, the FB-DIMMs are much less able to naturally scale their power consumption to fit the bandwidth needs of a given workload. So the higher bandwidth, greater capacity per pin-out, and RAS capabilities that FB-DIMMs offer come at the price of higher power consumption and reduced power efficiency when the system is under less than a full load.

http://arstechnica.com/news.ars/post...rver-room.html