The United States has retaken top place in the Top500 list after 5 years of supremacy by China. Computers constructed by IBM for the United States Department of Energy have pushed the previous 2 record-holders, both Chinese, into second and 4th place.
The world's fastest computer is now Summit, constructed by IBM for the DoE's Oak Ridge National Laboratory, with a performance of 122.3 petaflops (floating point operations per second).
It pushed China's 93-petaflop Sunway TaihuLight into second place after 2 years at the top.
In fact, it's a double win for IBM due to the fact that the company constructed another computer for the DoE, Sierra, and it's taken 3rd place, pushing another Chinese computer, Tianhe-2A into 4th. Both Summit and Sierra use IBM's Power9 processors with Nvidia accelerators.
Tianhe-2A held the leading slot from June 2013 to June 2016 before being deposed by Sunway. It has slipped down the rankings despite an enormous-- and massively efficient-- upgrade that almost doubled its computing power, from 33.9 petaflops to 61.4 petaflops, for a less-than-4-percent boost in power usage.