"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."
