The U.S. now has two machines atop the world’s supercomputer rankings, with a pair of IBM Corp.-built systems holding first and second place ahead of their Chinese competitors.

The latest edition of the Top500 List shows that the U.S. Department of Energy’s Summit supercomputer (pictured), which first secured the No. 1 spot in June, has increased its lead at the top. That machine now boasts a performance score of 143.5 petaflops thanks to a recent upgrade, up from 122.3 petaflops previously.

Meanwhile, Summit’s sister computer Sierra is the new No. 2, displacing China’s Sunway TaihuLight with a score of 94.6 petaflops following its own upgrade.

The Top500 List uses a mathematical test called Linpack to assess how fast the machines are at performing calculations. In the case of Summit, its processing power is equal to all of the humans in the world each performing 19 million calculations per second, which is a pretty impressive feat to say the least.

A second test, called the High-Performance Conjugate Gradient, is also used, and Summit and Sierra both came out on top here as well.

Supercomputers are generally used for research purposes, including tasks such as the virtual testing of nuclear bombs, trying to understand how the universe was formed, forecasting climate change and aerodynamic modeling for aircraft.

Summit is owned by the Oak Ridge National Laboratory and is designed for artificial intelligence workloads that pertain to high-energy physics and materials discovery, among other things. The lab claims it can perform more than 3 billion-billion calculations per second in some cases.

Sierra is jointly operated by the DOE’s National Nuclear Security Administration and the Lawrence Livermore National Lab.

Both machines are powered by a combination of IBM’s Power9 central processing units and Nvidia Corp.’s V100 graphics processing units. They’re enormous too, made up of numerous rows of refrigerator-sized computer cabinets. Summit boasts 2.4 million processor cores in total, while Sierra has 1.6 million.

The third and fourth most powerful supercomputers are both Chinese. TaihuLight has slipped down to third overall with a 93-petaflops performance, while Tianhe-2A takes fourth place with a score of 61.4. Rounding out the top five is Piz Daint, hosted at the Swiss National Supercomputing Center, with a score of 21.2 petaflops.

Chinese-built supercomputers still dominate the rankings overall, with 227 of the top 500 originating from that country. Meanwhile, the U.S. is home to just 109, a new all-time low.

Photo: Oak Ridge National Laboratory