IBM's Roadrunner cluster has once again claimed the title of fastest supercomputer in the world.

The Los Alamos research system extended its run at the top of the rankings with a top computing rate of 1.105 petaflops, more than one thousand trillion operations per second.

Roadrunner was unveiled last spring, and immediately jumped to number one on the March 2008 issue of the Top 500 Supercomputer list.

Roadrunner's lead did narrow significantly, however. Cray's Jaguar system at Oak Ridge National Laboratory became only the second system ever to break the petaflop barrier, with a speed of 1.059 petaflops.

Third on the list was the SGI Pleiades cluster at NASA's Ames Research Center, with a relatively pedestrian 487.01 teraflops, followed by the US Department of Energy's BlueGene/L cluster. The top nine supercomputing systems were all located in the US.

The Shanghai Supercomputer Center's Dawning system claimed the top international spot with 180.6 teraflops, while the top system in the UK was a 92.98 teraflop IBM Power cluster at the European Centre for Medium-Range Weather Forecasts in Reading.

Intel claimed the lion's share of the processors powering the Top 500 machines. Although the Roadrunner and Jaguar systems run on AMD chips (Roadrunner also uses a variation of IBM's Cell processor), Intel processors were found in 373 of the 500 systems, or 75.8 per cent.

AMD and IBM tied for second place on the chip tally, each powering roughly 12 per cent of the systems on the list.

The famous Apple-powered COLSA cluster continued its three-year run on the list, claiming the 310th slot. The self-made cluster was constructed by the Alabama-based technology services firm in 2005 from 1,562 Xserve G5 servers.