The federal government maintained its leadership in supercomputing with five of the top 10 of the world's most powerful machines under its management, according to a biannual list of the top supercomputers.

However, a Japanese supercomputer called K computer--run by the RIKEN Advanced Institute for Computational Science and developed by Fujitsu--remained No. 1 on the list for the second straight time, a position the feds are vying for with the development of a new supercomputer called Titan.

Four supercomputers run by the Department of Energy (DOE) and one by NASA remained among the top 10 most powerful in the world, all of them holding steady at their positions from a list of the top machines published in June.

Supercomputers on the biannual list are ranked by how quickly they can run calculations according to Linpack, a benchmark application developed to solve a complex system of linear equations.

[ Learn more about government supercomputers. Read Feds Detail Supercomputing's Future. ]

Several top supercomputer researchers compile the list--Hans Meuer of the University of Mannheim, Germany; Erich Strohmaier and Horst Simon of NERSC/Lawrence Berkeley National Laboratory; and Jack Dongarra of the University of Tennessee in Knoxville.

The U.S. government's most powerful machine on the list is a Cray system called Jaguar that is run by the DOE's Oak Ridge National Laboratory; it is ranked third overall. Moreover, the lab is currently building a system called Titan that researchers claim could eventually give K a run for the top spot.

Titan potentially will deliver 20 petaflops of performance at its peak, nearly two times faster than Japan's K computer, which hit 10.51 petaflops at its peak to reach the top spot on the latest list. Last year, K achieved 8.2-petaflop performance for its top ranking. "Flop" stands for floating-point operations per second, and a petaflop computer can perform a thousand trillion flops.

The other federal-run systems in the top 10 include a DOE Cray computer called Cielo at No. 6; an SGI system called Pleiades at the NASA Ames Research Center at No. 7; a DOE Cray system called Hopper at No. 8; and a DOE IBM system called Roadrunner at No. 10.

The National Oceanic and Atmospheric Administration and Department of Defense also were among federal agencies that made the top 500 with several of their supercomputing systems.

The government uses supercomputers for a range of research requiring high-computational processing, such as weather and climate simulations, space-technology development and testing, and medical research.

Rounding out the top 10 list are a Chinese supercomputer called Tianhe at No. 2; another Chinese system called Nebulae at No. 4; a Japanese supercomputer called TSUBAME at No. 5; and a system in France called Tera-100 at No. 9.

Indeed, if the list is any indication, supercomputers continue to achieve premium performance. The June list was the first time all of the systems in the top 10 achieved petaflop or greater performance, and all of the systems on the November list did as well.

Still, while K achieved a faster performance than the other systems to maintain its position, all of the others in the top 10 sustained the same peak performance from the June list.

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