Proving that performance isn't everything, the latest Top500 list of supercomputers for the first time also measures energy efficiency.

The latest ranking listed IBM's new Roadrunner as the most efficient on the list -- and the most powerful, at 1.026 petaflops, or 1.026 quadrillion calculations per second.

The list was unveiled last week at the International Supercomputing Conference in Dresden, Germany.

Jack Dongarra, a professor at the University of Tennessee and co-creator of the Top500 list, noted that Roadrunner still needs as much energy as an average-size shopping mall.

Top500 co-author Erich Strohmaier, a computer scientist at Lawrence Berkeley National Laboratory, attributed Roadrunner's efficiency to its use of both AMD Opteron processors and the Cell chips that run Sony's PlayStation.

"Roadrunner is the most powerful [system] and uses some of the most efficient technology," said Strohmaier.

Dan Olds, an analyst at Gabriel Consulting Group Inc., said that advances in technology should drive down the cost of running supercomputers before the next landmark performance level -- exaflop -- is reached.