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Computers

Upgraded US supercomputers claim top two spots on Top500 list

But China has more of the 500 fastest machines on the planet than ever, and the US hits an all-time low.

IBM built Lawrence Livermore National Laboratory's Sierra supercomputer.

IBM built Lawrence Livermore National Laboratory's Sierra supercomputer.

Randy Wong/LLNL

The US now can claim the top two machines on a list of the 500 fastest supercomputers, as Sierra, an IBM machine for nuclear weapons research at Lawrence Livermore National Laboratory, edged out a Chinese system that last year was the very fastest.

The Top500 list ranks supercomputers based on how quickly they perform a mathematical calculation test called Linpack. The top machine, IBM's Summit at Oak Ridge National Laboratory, had claimed the No. 1 spot in June with a speed of 122.3 quintillion mathematical operations per second, or 122.3 petaflops.

But an upgrade gave it a score of 143.5 petaflops on the newest list. To match that speed, each person on the planet would have to perform 19 million calculations per second. Sierra got an upgrade, too, boosting its performance from 71.6 petaflops to 94.6 petaflops and lifting it from third place to second.

Summit and Sierra are siblings, each using IBM Power9 processors boosted by Nvidia Tesla V100 accelerator chips and connected with Mellanox high-speed Infiniband network connections. They're gargantuan machines made of row after row of refrigerator-size computing cabinets. Summit has 2.4 million processor cores and Sierra has 1.6 million.

Supercomputers are used for tasks like virtual testing of nuclear weapons, aerodynamic modeling of aircraft, understanding the formation of the universe, researching cancer and forecasting climate change effects. They're expensive but prestigious machines that can keep scientists and engineers at the vanguard of research.

Supercomputers have gotten steadily faster on the Top500 list of the world's fastest machines, but those gains started faltering about a decade ago as chip performance slowed down.

Top500

The US once dominated the Top500 list, but China has steadily risen in clout. Its Sunway TaihuLight topped the Top500 for two years with a 93 petaflop score, and China extended its lead in the number of machines on the list.

A total of 227 of the Top500 machines are in China, compared with an all-time low of 109 for the US. The November list is the 52nd one released by a collection of academic researchers who compile it twice yearly for supercomputing conferences.

Linpack is only one speed test, though, and the Top500 has another designed to capture a broader range of performance abilities, the High-Performance Conjugate Gradient (HPCG) benchmark. On it, Summit and Sierra are head and shoulders above competing supercomputers.

Although Summit and Sierra use IBM's Power9 CPUs, the vast majority of Top500 machines use Intel processors. With the difficulties maintaining the performance increases described by Moore's Law, supercomputer makers have increasingly turned to various accelerator chips more specialized for mathematical calculations. Nvidia's chips, derived from its graphics processors, dominate this usage.

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