The energy consumed by data center servers, cooling equipment, and related infrastructure more than doubled in the United States and worldwide between 2000 and 2005, according to a new study.

A jump in the number of servers--especially lower-end servers costing less than $25,000--accounts for 90% of the additional power consumption, says the study's author, Jonathan Koomey, a consulting professor at Stanford University and a staff scientist at Lawrence Berkeley National Laboratory. The study was commissioned by Advanced Micro Devices, which is touting its energy-efficient processors. Only 5% to 8% of the increase in data center electricity consumption is attributed to power use per unit.

Driving the server proliferation is the insatiable appetite for Web content, such as video on demand, music downloads, and Internet telephony, Koomey says.

The total electricity bill to operate data center servers and related infrastructure equipment in the United States was $2.7 billion in 2005, compared with $1.3 billion in 2000. Worldwide, the total bill was $7.2 billion in 2005, compared with $3.2 billion in 2000.

Looked at differently, U.S. data center power consumption in 2005 was equivalent to about five 1,000- megawatt power plants, or five typical nuclear or coal power plants, Koomey says.

Data center servers consumed 0.6% of all electricity in the United States in 2005. When auxiliary infrastructure equipment, including network and cooling gear, is thrown in, that figure jumps to 1.2%, about the same percentage consumption as for televisions.

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Koomey suggests a number of things companies can do to lower their data center energy consumption: deploy virtualization software to reduce the number of physical servers; deploy more efficient cooling architectures; consider ongoing power and cooling costs when buying systems; or just change power supply products. "Power supply is a big thing, and that's just something you can drop in," he says.

Tech vendors are weighing in with more energy-efficient products. At the chip level, for example, AMD this year will introduce a quad-core processor that consumes about as much energy as older single-core products, says John Fruehe, AMD's business development manager. At the system level, Sun Microsystems' T1000 and T2000 servers are eligible for electric utility rebates in California because they consume less electricity than competing servers, says Subodh Bapat, VP of Sun Eco, a unit that oversees the company's green programs.

Fueling demand for more, cheaper servers has been the move to Linux and distributed platforms and away from "operating systems that charge per server," Koomey says. There's been a shift away from midrange servers, while high-end server volumes didn't change much from 2000 to 2005. Koomey estimated power use per type of server multiplied by the total installed base of servers, based on data from market researcher IDC.

In 2000, U.S. data centers housed about 5.6 million servers, of which 4.9 million were low end, 663,000 were midrange, and 23,000 were high end. By 2005, U.S. data centers housed 10.3 million servers, of which 9.9 million were low end, 387,000 were midrange, and 22,200 were high end.

Worldwide in 2000, data centers housed about 14.1 million servers, of which 12.2 million were low end, 1.8 million were midrange, and 66,000 were high end. By 2005, data centers worldwide housed about 27.3 million servers, of which nearly 26 million were low end,1.3 million were midrange, and 59,000 were high end.