On a Component Level
Once you have selected a processor, chipset, power supply, hard drive and other components, it’s time to compare the offerings on the market, and the available speed grades and model variations. It’s obvious that high clock speed products will provide more performance, but how important will the performance increase really be? A performance increase of less than 10% requires at least 20% more clock speed, which is hardly noticeable at all; hence it makes a lot of sense to stay within the affordable mainstream. A mid-speed Core 2 Duo processor will provide among the best energy efficiency, while the power consumption of fast versions will increase more noticeably than performance will.
Once you chose your processor, make sure you pick a reasonable clock speed. The highest speeds will increase power consumption more than performance. However, idle power consumption doesn’t vary too much between identical products at different speeds, as the idle clock speed typically is the same.
I already mentioned the issue with multiple voltage regulator phases on motherboards. If you go for a high-end product, it will feature anything from 6 to 12 phases to deliver power reliably, but energy efficiency suffers with every phase added unnecessarily. The motherboard makers are now aware of this, and equip their boards with mechanisms that detect the processor load and dynamically add or remove phases to regulate the processor voltage. Make sure you check for energy-controlling mechanism such as so-called Energy Processing Units (EPUs, from Asus) or limit yourself to a small number of voltage regulator phases if you don’t need your motherboard to support extreme overclocking.
Power saving mechanisms with graphics cards are not yet as sophisticated. In fact, most graphics cards in the upper mainstream and the high end consume more power than the entire motherboard with the processor. AMD’s ATI Radeon 3000 series is based on a 55 nm manufacturing process and provides the best performance per watt ratios at this time. Nvidia’s GeForce 9600 GT is a possible alternative that plays in the same league. However, both ATI and Nvidia are aware of this, and will increasingly be implementing power saving features into their desktop products. This should not be difficult to achieve, as these technologies have been available, but they were only used for mobile graphics solutions. If you want to be sure you minimize power consumption, then you cannot go for high-end graphics solutions, which require between 60 and 200 W per graphics card. Any fully featured mainstream card typically provides the best ratio of performance and performance per watt. Please look at our Best Graphics Cards for the Money May 2008 article for recommendations.
While power supplies can only be selected by power and by type (active/passive, cooling technology, and so forth) you can look for efficiency numbers. The industry rates its best products as “80+”, which means that they have an energy efficiency of 80%. This, however, doesn’t mean that they cannot be better, or worse. As with other components, energy efficiency depends on the particular load.
Hard drives can have a small impact on power consumption, as there are drives with multiple platters per drive and those with only a few or even just one platter. Terabyte hard drives are excellent examples, as there are models using five, four or even only three platters to store the same 1000 GB capacity. The fewer platters a drive is based on, the lower the power consumption.
