"If we were to develop this Tier 1 and then leave it in place indefinitely, I think it would not sufficiently recognize the most efficient products that emerged over time," he said. The idea will be to leave it in place for a limited period, while "on a slower track" the EPA figures out the type of "holistic measure" that it uses for other products, he said.

But the EPA has its work cut out for it even on the Tier 1 spec. It needs to work out which types of servers it will cover -- industry-standard servers with one to four processors are likely to be included -- and even the meaning of "idle."

"What's the definition of idle?" asked Mark Monroe, Sun Microsystems' director of sustainable computing. "How much of the OS has to be alive? Does idle mean it's responding to wake-on-LAN-type things, or is it truly in a bare minimum state?"

Like other vendors, Sun says it supports the Energy Star program in principle. But Monroe said the SPEC benchmarks being considered are untested and don't measure enough different kinds of workloads.

Some observers blame the server makers for the holdup. With customers paying more attention to power efficiency, vendors don't want to risk signing off on a specification that will make their products look bad, said Jon Peddie, president of Jon Peddie Research. "I think it is totally a political problem," he said.

He also questioned the usefulness of measuring efficiency at idle, especially as more companies are using virtualization to improve the utilization rates of servers. "It's like measuring miles per gallon when your car is sitting on the drive at home with the engine running," he said. "Who can use that?"

The difference, according to Howard, the EPA consultant, is that people don't leave their car engines running all night. But many data centers don't turn their servers off when they are not being used, because they are worried they won't come on again when needed.

Brad Brech, a distinguished engineer with IBM, said the measurements for the Tier 1 spec, though imperfect, will be a step in the right direction.

"I do believe we need more holistic measures as we go forward," he said, "but as with everything, having a good starting point gets the ball rolling."

The EPA is also working on an Energy Star rating for data centers, and Fanara said it will start to tackle storage equipment in the fourth quarter.