The specification aims to help customers identify the most power-efficient servers when making purchases. The Energy Star program already covers desktop PCs, monitors, light bulbs and dozens of other products. Products are identified with an Energy Star label.

The third draft establishes power consumption limits for when a server is in an idle state, something that had not been established in the second draft. To qualify for the Energy Star logo, vendors must also meet minimum requirements for power supply efficiency and publish a data sheet for each server indicating its power and performance levels for maximum, minimum and typical configurations.

The specification covers servers with up to four processor sockets. The EPA said it chose to exclude blade systems from the draft because SPEC indicated that its for measuring idle consumption can't run on blades. Future specifications will "look for appropriate ways to address blade systems," the EPA said.

The specification is due to take effect on Feb. 1, 2009. A more comprehensive "Tier 2" specification planned for October 2010 may include servers with more than four sockets.

The idle power limits have been set at 60 watts for one-socket systems and 271 watts for four-socket systems. Additional components are given an additional power allowance. For example, a second hard drive gets an additional 15 watts of power.