Latest ranking of the speedy machines includes old favourites such as IBM's Blue Gene/L, plus a few surprises

It was November 2000 when the first supercomputer passed four teraflops, or four trillion calculations per second. Now, that's the minimum requirement to even show up on the latest version of a list of the 500 fastest machines.

Supercomputing, which pits the highest-end machines against challenges such as forecasting the global climate in coming decades or finding oil reservoirs underground, is a fast-changing field. The Top500 list, released twice annually at supercomputing conferences, has the most turnover compared with the preceding list yet, according to the researchers who compile it.

Many systems on the newest Top500 ranking, set to be released on Wednesday at the International Supercomputing Conference in Dresden, weren't on the list at all when the last one was released in November 2006.

But one familiar supercomputer, IBM's Blue Gene/L at Lawrence Livermore National Laboratory, again topped the Top500 Supercomputer Sites list with 131,072 processors, staying far ahead of its closest competitors by achieving speeds of 280.6 teraflops. The big change is Cray's Jaguar system, which leapfrogged from the number 10 to the number two position. The only two other systems to surpass 100 teraflops were also made by Cray: Oak Ridge National Laboratories' Jaguar, at 101.7 teraflops, and Sandia National Laboratories' Red Storm, at 101.4 teraflops.

The total performance of all 500 systems reached 4.92 petaflops, or 1,000 teraflops. The systems on the November list topped out at 3.54 petaflops, and the June 2006 compilation totalled 2.79 petaflops.

IBM dominated the list with six of the top 10 systems and 192 of the total 500, though HP is actually the overall leader in terms of the percentage of systems. Forty percent, or 203 of 500, are powered by HP, but IBM's total teraflop sum is 2,060, almost double HP's total of 1,202.

Coming in at number five, IBM's New York Blue at Stony Brook University is new to the list, as is IBM's similar Blue Gene system at Rensselaer Polytechnic Institute at number seven. Dell's Abe PowerEdge 1955 server, at the University of Illinois' National Center for Supercomputing Applications, made its at the number eight spot.

The main measurement used in compiling the list is the Linpack measurement, which puts each system through its paces by having to solve a dense system of linear equations. The Top500 acknowledges it isn't a complete test of system performance, but it's a way to test for performance on a similar problem across each system. The need for a more complete benchmarking system has been under discussion for several years.

Intel managed to increase its lead over AMD in the number of systems using x86 processors. Just over half — 52 percent — of the systems use Intel's x86 chips, up from 45.6 percent, while AMD's share shrunk from a 22.6 percent share to 21.2 percent. Intel's Itanium processors are beginning to move off the list, appearing in 28 of the 500 systems, down from last year's count of 35.

The most noticeable change in applications of supercomputing is the rise in the number of systems used in geophysics, which rose from 23 in November to 37 on the newest list.

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