So what's the takeaway here? I'm certainly not going to blare out that AMD chips are, hands down, more energy efficient than Intel's -- though I will acknowledge that in Nelson's previous tests (which you can read about here, here, and here), AMD CPUs have had an edge in this department. Will this picture change with the arrival of Intel's Nehalem Xeon? Nelson is eager to find out, just as soon as he can get his hands on Intel's new CPU.
Regardless of which CPU wins the green prize, clearly there can be significant differences among servers, not just in terms of raw performance but also energy consumption and efficiency. For large datacenters, a difference of 50 watts per server per hour will add up to real money. Any organization that is concerned about its utility bills, its power budget, or its carbon footprint would benefit from testing servers before investing heavily in them. Make sure they meet not only your raw performance needs but also your energy efficiency needs. Because the last thing you want is a datacenter full of Hummers when a fleet of hybrids would work just as well -- for far less.