IBM's Blue Gene still heads the Top 500 list of supercomputers, though AMD's Opteron processor has made good progress.

Retaining the number-one spot on the biannual list for the fourth time, IBM's BlueGene/L System at the US Department of Energy's Lawrence Livermore National Laboratory recently reached a Linpack benchmark performance of 280.6 teraflops (trillions of calculations per second). No other system has yet passed the 100-teraflop mark.

IBM supercomputers accounted for about half of the overall list, which was released at the International Supercomputing Conference, with HP taking nearly a third.

The Top500 list, known for its rapid turnover, was slower in that respect this year. Some 158 systems were bumped this time around, compared with more than 200 systems displaced in the June 2005 list. But in the fast-paced world of high-performance supercomputing, no systems maker can afford to rest on its laurels for long, especially at the high end of the list.

"The thresholds to get into the top 50 move fast; machines are there one day, gone the next," said Herb Schultz, manager for IBM Blue Gene.

"In the next six months you should see discussions about what's next. It's no secret Blue Gene has been in the market for a little while, and we're looking at ways to make the chips faster, get more chips on a core, and do a faster job of interconnecting nodes. So you could expect to see a product with the same architecture, but that's faster and maintains the same power and cooling envelope as the current Blue Gene does," Schultz said.

Among other trends on the list, Intel microprocessors powered 301 of the systems, which was down from 333 last year; while AMD's Opteron processors gained some ground to account for 81 systems, compared with only 25 systems one year ago.

Most of the supercomputers on the list – nearly 300 – are housed in the US; Europe now has 83 systems, which is down from the 100 systems they had six months ago. Meanwhile, Asia has 93 systems, which is up from 66 six months ago.