Its peak performance is expected to be 360 teraflops, and will fit into 64 full racks. It will also cut down on the amount of heat generated by the massive power, a big problem for supercomputers.

The final machine will help scientists work out the safety, security and reliability requirements for the US's nuclear weapons stockpile, without the need for underground nuclear testing.The Earth Simulator has held on to the top spot since June 2002. It is dedicated to climate modelling and simulating seismic activity.

But in September, IBM said that another Blue Gene/L machine clocked up 36.01 teraflops, marginally surpassing the Earth Simulator's performance.

This was achieved during internal testing at IBM's production facility in Rochester, Minnesota though, so was not an official record.Another giant to enter the fray is Nasa's Columbia supercomputer based at its Ames Research Center in California. Its mission is to model flight missions, climate research, and aerospace engineering.

The Linux-based machine was reported to have reached a top speed of 42.7 teraflops a second in October.

Great challenges

Supercomputers are hugely important for working out very complex problems across science and society.Their massive simulation and processing power means they can improve the accuracy of weather forecasts, help design better cars, and improve disease diagnosis, as well as environmental research.

IBM's senior vice president of technology and manufacturing, Nick Donofrio, believes that by 2006, Blue Gene will be capable of petaflop computing. This means it would be capable of doing 1,000 trillion operations a second.

"When you get a computer as large as a petaflop, you can start to think of simulations that might complement the physical world," Mr Donofrio recently told the BBC News website. "You can start to be more proactive, more interactive and more innovative."

One area where Mr Donofrio sees supercomputing, and Blue Gene machines in particular, as crucial is health. He sees the machines as being able to help scientists understand one of the greatest challenges of the 21st Century, protein folding.

"Health is one of the most important problems, not just mapping the human genome, but also protein structures. "We are a great believer in simulation. It gives you another tool," he said. Once the structure of proteins are understood fully, then drugs can be tailor-made to fight diseases more effectively.

Compared to the current fastest supercomputers, Blue Gene is designed to consume one 15th the power and 10 times more compact. Since the first supercomputer, the Cray-1, was installed at Los Alamos National Laboratory in 1976, computational speed has leaped 500,000 times. The Cray-1 was capable of 80 megaflops (80 million operations a second). The Blue Gene/L machine that will be completed next year will be five million times faster.