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The personal computer may be one of the most revolutionary and wildly successful consumer products of all time. In the 1990s, the number of U.S. households owning computers jumped from 14.8 million in 1990 to 60 million in 2001 as consumers embraced digital photography, e-mail, and a plethora of new applications made possible by personal computers[1,2]. On the job, over half of America’s workforce today uses a computer. In a very short span of time, computers have become central to the economy and our daily lives. But the computer revolution has also entailed a rapid growth in energy consumption to power personal computers (PCs) and the network infrastructure that make the Internet possible. Computers – including desktops, laptops, and even servers – are ripe for energy efficiency improvements.

What do we mean when we say "computer"?
When we talk about computers at EfficientProducts.org, this encompasses a vast array of products, some of which are typically used by consumers or small offices, and a small fraction of which are only used in high-end data center or scientific applications. To help eliminate some of the confusion, below are definitions of some common computer types:

Desktop: a stationary computer used in home or office settings that usually requires additional user interface peripherals such as a keyboard, mouse, and monitor in order to operate.
Integrated desktop: a desktop computer whose monitor and computer hardware (such as the central processing unit (CPU), video hard and hard disk drive (HDD)) are located in the same physical housing (e.g. Apple’s iMac G5).
Workstation: a desktop computer with high-end graphics, processing, and storage capabilities. Workstations are typically used in professional video production, 3D rendering, and science/engineering applications and often contain multiple processors, dual graphics cards, etc.
Laptop/notebook: a computer designed for portable operation that usually includes an integrated keyboard, track pad, and monitor and that is able to run independent of electricity from an AC wall plug through use of an onboard battery or other energy storage device.
Desktop-derived Server: a subset of servers that are similar in configuration and performance to many desktop computers. These servers are less powerful than those found in data centers and are typically used in small office environments to share printers/files and provide Internet connectivity.

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How many computers are in use and how much energy do they use?
In 2004, there were 150 million desktops, 50 million laptops, and about 10 million desktop-derived servers in use in the U.S. To put these figures in perspective, there are approximately 111 million households in the U.S. today[3],meaning that there is now more than one desktop or laptop in use per U.S. household. Over half of American households own one, and over half of the American work force uses one on the job[4]. These numbers are expected to continue climbing, since more than 50 million new units are sold every year[5], and many consumers continue to use their old computers even when they purchase new ones.

The average desktop computer (without its accompanying monitor) now consumes 200 to 400 kWh per year of electricity (nearly as much as a highly efficient refrigerator). Laptops consume about 80 to 140 kWh per year, and desktop-derived servers consume about 1,500 kWh per year (as much as a typical home uses annually for all electric lighting). In total, the above mass-market computers represent about 2 to 3% of all U.S. electricity consumption. The nation pays an electric bill of more than $6 to $10 billion per year for its computers, and the resulting carbon dioxide emissions from power plants represent about 1% of the national total. Out of all appliances, the U.S. Department of Energy has identified computers as the one whose energy use is growing the fastest[6].

Computer Environmental Impacts

Computer Type	Annual Energy Use (kWh)	Electricity Cost (USD) [7]	CO₂Emissions (lbs.) [8]
Desktop	200 - 400	$16 - $32	268 - 536
Laptop	80 - 140	$6 - $11	107 - 188
Server	1,500	$120	2,012

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How can I find today's most efficient computers?
The U.S. Environmental Protection Agency’s (EPA) ENERGY STAR program, 80 PLUS, and Climate Savers Computing Initiative (CSCI) all maintain criteria for computer efficiency. 80 PLUS and CSCI both rate the efficiency of internal power supplies. The current ENERGY STAR label v4.0 signifies that the computer meets a series of energy efficiency criteria, including low Idle, Sleep and Standby mode power as well as 80 PLUS power supply efficiency. For more information on these programs and compliant products please visit the ENERGY STAR, CSCI, and 80 PLUS websites.

Here are a few helpful tips that can help you identify the most efficient and cost-saving computer for your needs:

If purchasing a desktop, look for models that bear the ENERGY STAR and/or 80 PLUS logo.
Check out EfficientProducts.org research on new computing technologies that can boost the efficiency of a computer far beyond ENERGY STAR requirements.
Purchase a computer with enough performance to meet your computing needs, but no more. For most users that are purely interested in office applications, web surfing, and e-mail, a laptop computer is the ideal choice. Laptop computers typically use less than a third of the energy of a desktop computer and monitor. If you still need a desktop computer, consider some of the newer “mini” style computers that incorporate highly efficient laptop components but have performance comparable to other desktops.
Look for energy-saving computer processor technologies such as AMD’s Cool’n’Quiet technology or Intel’s Enhanced Intel SpeedStep (EIST). Processors with these features scale back power consumption when the computer is not being heavily taxed by the user and can cut power consumption by up to 20% when the computer is idling.

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What is the definition of efficiency for computers?
When the ENERGY STAR program began labeling energy-efficient products in 1992, one of the first product categories that the program chose to tackle was computers. ENERGY STAR first began labeling desktop computers based on whether they could enter a low-power “sleep” or “standby” mode when not in use.

Since the inception of ENERGY STAR’s landmark computer specification, efficiency advocates and industry have labored to identify and promote new areas for energy efficiency improvements in computers. Most recently, ENERGY STAR version 4.0 included active mode with the requirements ranging from 50 to 95 W.

One current utility-sponsored efficiency program that also addresses active mode efficiency is the 80 PLUS program. Operated by Ecos Consulting, the 80 PLUS program promotes the sale of desktop computers and desktop-derived servers that contain highly efficient power supplies. Climate Savers Computing Initiative, started by Google and Intel, also promotes effieicncy through power supplies. Since all of the computer’s electrical power must pass through its power supply, highly efficient power supplies can result in substantial energy savings that are completely transparent to the user. For more information about the 80 PLUS program or CSCI, please visit www.80PLUS.org and www.climatesaverscomputing.org.

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Is there a way to test efficiency?
Typically, computer efficiency can be tested by measuring the system’s power consumption (not including the monitor) in different modes of operation, using a power meter. For some of the latest ideas on these test methods and some hypothetical holistic measures of computer efficiency, we recommend that you visit the ENERGY STAR program’s web page documenting the ongoing revision process for the computer specification.

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U.S. Census Bureau, Statistical Abstract of the United States: 1994 (114th edition), Washington D.C., 1994. p. 742
U.S. Census Bureau, Statistical Abstract of the United States: 2004 – 2005 (124th edition), Washington D.C., 2004. p. 621
U.S. Census Bureau… 2004. p. 50
U.S. Census Bureau… 2004. p. 407
Michelle Kessler, “Roaring laptop sales boost PC market,” USA Today, January 25, 2005, p. B1.
See Michael Thelander, “IT and the $8 Billion Electric Bill,” IT Professional, November/December 2004, pp. 49-56 and www.eia.doe.gov/oiaf/aeo/overview.html#consumption.
Assumed average utility rate of $0.08 per kWh of electricity. See www.eia.doe.gov.
Assumed average electricity generation profile, resulting in 1.341 lbs. CO₂ emissions per kWh electricity generation. See U.S. Department of Energy, U.S. Environmental Protection Agency, Carbon Dioxide Emissions from the Generation of Electric Power in the United States, Washington D.C., July 2000. p. 2

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What's New?

How Low Can We Go? A White Paper on Cutting Edge Efficiency in Commercial Desktop Computers
This white paper discusses in detail the results of recent efficient desktop computer research conducted by Ecos and EPRI, demonstrating savings of 40% to 70% over computers meeting today's ENERGY STAR v4.0 desktop requirements.

How Low Can We Go? Pushing the Limits of Efficiency in Desktop Computers
This 4-page brief discusses cutting edge technologies that can slash the energy use of today's PCs using almost entirely off-the-shelf components.

How Low Can We Go? Presentation from 2008 APEC, Austin, TX
A more detailed look at highly efficient desktop computer builds.

Research

How Low Can We Go? Presentation from 2008 APEC, Austin, TX
A more detailed look at highly efficient desktop computer builds.

NRDC Laptop Efficiency Summary
A 4-page summary of NRDC's laptop efficiency research.

NRDC Laptop Efficiency Report
A detailed report on efficiency opportunities in laptops.

Test Methods

NRDC Draft Idle Mode Test Method
Proposed test method for testing the power consumption of a computer when it is idling, drafted by the Natural Resources Defense Council (NRDC).

Internal Power Supply Test Method
Thorough test method in development to test internal power supplies such as those found in computers.

Programs and Policies

ENERGY STAR computer specification

ENERGY STAR computer specification revision

80 Plus Program

Australian Greenhouse Office: Appliance Energy Programs

Top Runner

TCO Label for Computers

Other Useful Info

Scientific American: Power-Thrifty PCs

Silent PC Review

Xbit Laboratories