"The test setup consisted of an opened-up desktop PC, a P3
International Kill-a-watt meter and a collection of peripheral
cards and disk drives. The Kill-a-watt has a 1W resolution, if a
reading alternated between 2 values such as 8 and 9 Watts, the
estimated value was called 8.5 Watts. Some of the measurements made
were small enough that they were "in the noise". Other variables
included devices with inconsistent power usage and inconsistent
line voltage. The resulting measurements were actual power used by
the power supply, this may vary from the DC power used by the
tested components. Lastly, the Kill-a-watt meter also shows power
factor; a fairly consistent value of 0.67 was read.
"The tests were performed on the machine while it was in a
number of different software states. Many of the tests were done
while at the BIOS prompt, disk drive and network adapter tests were
done while the machine was running Linux (Ubuntu 8.10). Power
consumed by external devices such as the LCD video monitor and
amplified speakers was not taken into account. When a peripheral
such as a disk drive was removed for a test, the drive was
disconnected from power and the interface cable was removed to
eliminate possible power consumption by bus termination
resistors."
