What have we learned from our power requirement evaluation? First of all, it is important to make one essential decision: Do you need high 3D graphics performance? If the answer is yes, then we have to disappoint all of your low-power PC ambitions, as any graphics card capable of accelerating your heartbeat will also accelerate the electricity meter. You cannot get away with less than 40 W idle power requirements (when it only displays Windows) and 80 to 200 W power consumption in 3D mode just for the graphics card.
Let's be very clear about that, because 100-150 W is the power you need to run an entire, high-end dual-core PC with integrated graphics and a 20" TFT display! I can't help but criticize both AMD/ATI and Nvidia for not having gone against those absurdly high power requirements when their products don't have to do more but display rather static 2D information. Obviously, nothing changes as long as no one complains, because the technology for lower-power graphics solutions is already there, as we can see with mobile graphics chips.
If you still want to go with discrete graphics, which is a must for gamers and enthusiasts, pay close attention to what you buy. Stay away from the top models, as these are as power hungry as an entire PC, including the display. And you can save a lot of power by opting for upper-mainstream cards instead of high-end models; a GeForce 8600 GTS requires half the power than the 8800 GTS, but it's clearly not only half as fast. A low-end graphics card doesn't make much sense to us either, as it won't deliver enough performance for serious gaming, yet adds at least 20-25 W to the system's idle power requirements. If you want discrete graphics, go with an upper-mainstream card.
The processor is the most-popular component to actively influence system power requirements. Don't go with a single-core processor based on the false assumption that you might save some energy by eliminating the second core as you'll lose a lot of performance. Instead, we recommend going for an entry-level dual-core processor, because both AMD's and Intel's offerings stay well below the 15-W idle power requirement. AMD still offers the least idle power requirements, especially if you go for a 65-nm Athlon 64 X2 processor, while Intel's Core 2 family has the least maximum power requirements. More core and FSB clock speeds, as well as faster memory devices, mean higher power requirements. Thus, stay with what you really need.
Lastly, pay attention to the power supply, as its efficiency has an impact on the effective power requirement of the entire system, including each component you selected carefully. Whether or not a PSU has a 75% or 85% efficiency (at the 20-40%load level it mostly runs at) has a measurable impact on the power requirement and can totally negate any power-savings measures you may have taken.