IBM claims top four 'greenest' supercomputers, and 18 of top 19

Roadrunner is world's fastest, but fourth most efficient

IBM built the world's fastest supercomputer, and can now lay claim to building 18 of the world's 19 most efficient.

The recently released Green500 ranking takes the list of the world's 500 fastest supercomputers and re-orders them based on efficiency, as measured by performance per watt. No company dominates this metric quite like IBM.

Big Blue's Roadrunner system at the Department of Energy's Los Alamos National Laboratory has maintained the lead spot in the Top 500 Supercomputer Sites, which ranks machines by raw speed. But Roadrunner came in fourth place in the green list, behind three other IBM installations.

The world's most efficient is an IBM BladeCenter cluster at the University of Warsaw, which produces 536 MFlops for each watt of energy used. An MFlop is equal to 1 million floating point operations per second. In terms of raw speed, the Warsaw computer is the 422nd fastest.

Two IBM computers tied for second place in the Green500 list: another machine at the Department of Energy and one at IBM's Poughkeepsie Benchmarking Center. The first non-IBM machine clocked in at No. 5, that being the Greatly Reduced Array of Processor Elements with Data Reduction (GRAPE-DR) system at the National Astronomical Observatory of Japan, which produced 429 Mflops per watt.

IBM's Blue Gene design, introduced two years ago, took every spot on the Green500 list from No. 6 through No. 19 due to various clusters throughout the world that use the technology.

The 20th most efficient supercomputer is an NEC cluster using Intel Xeon processors deployed at the University of Stuttgart. Overall, IBM said it claimed 57 of the top 100 positions on the Green500 list.

The list is published by and sponsored by SuperMicro. The latest version is the fifth edition of the biannual ranking.

The average efficiency of computers on the Green500 list increased 10 per cent, from 98 MFlops per watt to 108 MFlops per watt, according to At the same time, aggregate power increased by 15 per cent from 200 to 230 megawatts.

One notable trend has commodity processors competing more strongly against custom-made models.

"Four- and six-core commodity processors keep improving in energy efficiency and surpass previous-generation custom processors," according to Green500. "Now, 20 of the top 50 energy-efficient supercomputers utilize commodity processors."

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