A partially built supercomputer has kept its spot at the top of the list of most powerful machines on the planet.

The BlueGene/L machine currently under construction at the Lawrence Livermore National Laboratory in the US was crowned top number-cruncher.

Its current processing peak of 136.8 teraflops will be doubled by time construction work is completed.

As a result, the organisation drawing up the list expect it to dominate the rankings for some time to come.

Big numbers

The Top 500 list is drawn up every six months and is a snapshot of the most powerful machines on Earth.

IBM's BlueGene/L took the top spot for the second time largely because its processing capacity doubled in size since the last list was drawn up.

When it is finished the machine will use 65,536 processors to tackle problems such as molecular dynamics, metrial modelling as well as turbulence and instability in hydrodynamics.

In the last list, released in November 2004, the machine's peak performance was 70.72 trillion calculations every second - a measurement known as teraflops.

The machine in second place is also a BlueGene system that was recently installed in IBM's Thomas J Watson Research Center in New York. At its peak that machine has proved capable of cranking through 91.2 teraflops.

As well as dominating the top two places, IBM is the dominant supplier of supercomputers on the list. In all 51.8% of the machines on the list sport its badge.

Silicon Graphics, NEC, Hewlett-Packard and Cray all have machines in the list. Cray's newest machine, the Red Storm, made it to the number 10 slot on the list.

Top supplier of the chips to do the number crunching was Intel. Its hardware was used in 333 of the systems listed. Also, five of the top 10 machines listed by the Top 500 organisation are BlueGene computers.

Third in the Top 500 list was Nasa's Columbia supercomputer at the Ames Research Center in California.

In the six months since the last list was drawn up half of the computers listed have been replaced by more powerful machines, a testament to the pace of innovation and to the increasing power found in silicon.

The basic power requirement needed to get on to the Top 500 list is 1.166 teraflops, a leap upwards from the basic 850.6 gigaflops benchmark from the November 2004 list.

The Top 500 list is compiled by Hans Meuer of the University of Mannheim in Germany, Erich Strohmaier and Horst Simon of NERSC/Lawrence Berkeley National Laboratory in the US and Jack Dongarra of the University of Tennessee in Knoxville.

The 25th edition of the list was unveiled at the International Supercomputing Conference held from 21-24 June in Heidelberg, Germany.