I'm upgrading my SageTV server which idles at ~85W with a Q6600, Asus mATX board, 2x2GB RAM, Corsair 450W PSU. Looking at several alternatives, will also create an additional file server too. Inspiration from Matt Garmin, Green Frank, others here, and a LOT of reading on German website Hardwareluxx, some real low power nuts.
Common components, wired PS/2 keyboard, USB mouse, onboard graphics ==>VGA==> LCD monitor
1) AMD Sempron 140 unlocked to dual core, Asus M4A785-M, 2x1GB RAM, Intel Pro PCI-e x1 NIC (uses 2W), 3.5" WD 640AAKS OS drive, 3 Samsung 2TB drives, Seasonic 300W Bronze PSU
Using heavily modded Kstat10 settings, shut off unused devices in BIOS. Same readings if single or dual core.....scratches head. Asus EPU-4 software no diff.
Win7 OS power save mode etc.
p0 @2700MHz 1.0875V = 84W with Prim95 running
p1 @1900MHz 0.9250V = 74W " " "
p2 @1500MHz 0.8375V = 69W " " "
p3 @ 800MHz 0.7125V = 64W " " "
Idle at 41W
Max CPU 84W (running Prim95 large FFT)
2) Intel DH61WW, i3-2100, 1x4GB RAM, 3.5" WD 640AAKS drive, Seasonic 300W Bronze, updated BIOS (adds tabs, not many useful options though), shut off parallel/serial ports, sound, etc. No other tweaking done.
Win7 OS power save mode, etc.
Max CPU 51W (running Prim95 large FFT)
Idle Ubuntu 11.04 "Natty" 23W
Adding in the 3 additional Samsung 2TB drives idle is 39W, with drives "spun down" idle is 28W in Ubuntu desktop. Unity, yuck.
Tested using KillaWatt. Sylvania 75W light bulb measures 73W, generic 40W was 39W, and generic 100W was 91W. I am not sure about these cheapo bulbs, trust the meter more.