PC Power Consumption: Personal Computer power consumption varies with a number of factors. The factors have shifted somewhat over the years. In early years, most of the power went to support circuitry. As time has gone by, the support circuitry has been shrunk into "chipsets" that use much less power whereas CPUs have become far more complex and power hungry. As of 2001 the largest power consumer is the CPU.

Understanding of power usage has been obfuscated by the fact that PC power supplies are typically rated to deliver much more power than is required by the PC. This is apparently done in order to handle start up surges. Even though PC power supplies are usually rated at 200 watts or more, typical desktop workstation power usage is around 50 to 80 watts. CRT Monitors also require 50 to 80 watts -- dropping to 30W or even lower, often in multiple "sleep" stages. Printers typically require about 30 watts although the heat lamp in a laser printer can require much more during the brief intervals when it is on. Laptops typically require 20-40 watts total when in use. Servers may require considerably more power than a desktop PC because of their use of massive memories and multiple hard drives.

FERC Energy Star ratings require monitor and PC consumption of 30 watts each, but achieve this by dropping the equipment into standby modes. Unfortunately, PC software often has substantial difficulty returning to normal operation from a reduced power mode and users require training to distinguish between a sleeping monitor and a powered off PC. It is possible to use these modes, but configuring a PC and monitor and training users can require a great deal of time and resource -- perhaps costing more than the energy saved. Since "Energy Star" equipment is not much more efficient when being used than normal equipment, power savings occur only when the PC is powered on but is unused. Typical savings are estimated at about 25%. Even Energy Star equipment should probably be turned off at night and on weekends.

Energy Star has a plethora of requirements including shipping with energy saving modes enabled and the ability to monitor networks in sleep mode if equipped with a network interface.

Power On 115W[L]; booting 75-85W[L]; Idle 68W[L]

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Note since 2001 the trend has been for CPUs and video cards to use even more power. Most other components require less power. Memories require less power per bit every year, but they tend to have many more bits each year and are clocked faster. A PC166 256MB RAM module is estimated to dissipate about 5watts when heavily loaded.

Return To Index Copyright 1994-2002 by Donald Kenney.