Conclusions
We've learned a few things from our testing. On the performance front, Intel's dual-core Xeon processors generally lead AMD's Opterons across a range of applications. AMD could no doubt edge closer to the Xeon 5160's performance levels with higher CPU clock frequencies—consider the performance of the Quad FX desktop platform, for instance, or the potential of the Opteron 2220 SE at 2.8GHz—but those gains would surely come at the expense of power efficiency. And no mere 200MHz (or even 400MHz) clock speed bump is likely to erase the Xeon 5160's performance advantage entirely. Furthermore, Intel's new quad-core Xeon 5355 CPUs are absolutely second to none among x86-compatible server/workstation processors, with no peer in sight. Provided you can supply them with a workstation-class workload that uses more than four threads—or pretty much any server-class workload, since those tend to involve more parallel work—a pair of Xeon 5355 processors will easily outperform any competing solution in this price range. These quad-core Xeons deliver a tremendous amount of computing power to a relatively inexpensive two-socket infrastructure.

On the power efficiency front, we found both Xeons and Opterons to be very good in specific ways. The Opteron 2218 is excellent overall in power efficiency, and I can see why AMD issued its challenge. Yes, we were testing the top speed grade of the Xeon 5100 and 5300 series against the Opteron 2218, but the Opteron ended up drawing much less power at idle than the Xeons—a reality that switching to a lower Xeon speed grade won't remedy, since all of these Xeons share the same 2GHz minimum clock speed via DBS. Thanks in part to their lower idle power draw, the Opterons also fared best in power efficiency when measured over a set span of time in which a task was accomplished—a fair cross-section of a moment in the life of a system. Finally, the Opteron 2218 system was close to the top in terms of efficiency when we measured the energy used to complete a task, whether it was rendering a scene with POV-Ray or doing a search with MyriMatch. This broad strength across multiple measurements of power efficiency, combined with a reasonably good showing in our performance tests, confirms that AMD's Socket F Opterons make a compelling recipe for power-efficient performance.

We've learned that multithreaded execution is another recipe for power-efficient performance, and on that front, the Xeons also excel. The eight-core Xeon 5355 system managed to render our multithreaded POV-Ray test scene using the least total energy, even though its peak power consumption was rather high, because it finished the job in about half the time that the four-way systems did. Similarly, the Xeon 5160 used the least energy in completing our multithreaded MyriMatch search, in part because it completed the task so quickly. The Xeon systems' high power consumption at idle makes them less-than-ideal in terms of overall power efficiency, but they are quite good in terms of energy expended per task. The more fully occupied they are with useful work, the more efficient they become.

The server/workstation CPU picture may change soon when AMD's new 65nm Opterons arrive. These 65nm chips could bring higher clock speeds and lower power use to some degree. However, AMD isn't likely to catch up to Intel on performance until at least mid-2007, when its new quad-core Opterons with a revised microarchitecture arrive. Between now and then, the market will likely remain divided, with Xeons holding the undisputed performance crown and Opterons offering a nonetheless attractive mix of power-efficient performance.