We expected that it would be hard to get the Core i5-661 system to run at only 25W idle power, but it turned out that the entire project was pretty easy to execute. Our test results show impressively that matching the power supply to your expected output (with some power reserves, of course) is imperative. Replacing the high-output 750W PC Power and Cooling PSU, which is a neat piece of hardware for a high-end gaming rig, with a low-power 220W PSU made the largest difference in our efforts to lower system power. Everything else is secondary. Voilà—26W reached with zero performance impact.
22-28W Idle Power is Realistic
We tried running the system with only one DDR3 DIMM module instead of two, but found that the savings are below 1W. At the same time, this measure would have had a noticeable impact on performance. This also applies to the hard drive, but we were able to save an additional 2W to 3W there. Still, even if you only pick a suitable power supply and optimize component voltage, it's absolutely possible for anyone to recreate our 25W build—assuming that you go for the latest mainstream 32nm Intel hardware and a motherboard with the H55/H57 chipset. The voltage reduction reduced peak power, but had little impact on idle power.
Let me come back to the question of why this is relevant. For power users, it really isn't. You'll probably go straight to a quad-core machine and not bother with power consumption questions. For average users, it becomes relevant if you want to go for a low noise system, or if you intend to pair high performance with the lowest possible acoustic footprint. This is typical of an HTPC, living room machine, or home server application. Keep in mind that a 3+ GHz Core i5 dual-core system is significantly faster than any other dual-core configurations around. It's finally possible to get strong performance at the power consumption levels of a dreadfully-slow Atom machine.
Intel’s Low Power Platform Means Higher Cost
However, there is a significant catch: you have to be aware that the new Intel platform is not a bargain. The processors are expensive, especially if you look at AMD’s pricing in comparison. Obviously, AMD has to stay aggressive on pricing to remain competitive from a performance perspective, but the result really makes you wonder. Do you really need to spend several hundred bucks on a Core i5 solution to reach the lowest power, or will an AMD solution at half the cost, but higher power consumption, be more suitable? We've made it clear that energy cost isn’t really an issue at this low level. If you want to go for the lowest power, for whatever reason, Clarkdale-based Core i5 processors paired with suitable components are unbeatable. They're just expensive relative to the competition, which is why we continue to recommend the i5-750 to enthusiasts at the $200-ish price point where you find the i5-661.