IBM produces the most powerful and energy efficient computers on the planet, according to the latest supercomputing Green500 list from Green500.org.

The top 20 most efficient supercomputers are built by IBM, or use the company's high performance computing technology, according to Green500.org; overall Big Blue holds 39 of the top 50 positions, in a list made up of computers used in astronomy, meteorology and pharmaceuticals research.

"Modern supercomputers can no longer focus only on raw performance. To be commercially viable these systems must also be energy efficient," said David Turek, vice president of Deep Computing at IBM.

"IBM has a rich history of innovation that has significantly increased microprocessor energy efficiency. We have also driven advances that include our Cool Blue technology portfolio, and added to our Project Big Green solutions designed to simultaneously reduce datacentre costs and energy use."

A list of the top 500 green supercomputers was first suggested in April 2005 during a keynote by Dr Wu-chun Feng at the International Parallel & Distributed Processing Symposium Workshop on High-Performance, Power-Aware Computing. This year's report is sponsored by components company Supermicro.

Overall, the most energy efficient system in the world is a supercomputer based on QS22 Blade servers at the University of Warsaw's Interdisciplinary Centre for Mathematical and Computational Modelling. According to IBM this produces more than 536 million floating point operations per second per watt of energy.