The Summit supercomputer at Oak Ridge National Laboratory remains the world’s most powerful, according to a ranking list released Monday.

It’s the third time that Summit, a IBM-built supercomputer, has been number one on the semiannual TOP500 list of of the world’s most powerful supercomputers. Summit debuted at number one in June 2018. That was the first time since 2012 that the United States had the most powerful supercomputer in the world. Summit retained the top spot in November.

The Sierra supercomputer at Lawrence Livermore National Laboratory in Livermore, California, remained at number two on the list released Monday, after climbing there from number three in November. The United States continues to have the top two systems in the world, a position that China held a year and a half ago.

Officials celebrated the launch of Summit in a ceremony attended by U.S. Energy Secretary Rick Perry on June 8, 2018. The supercomputer is capable of 200 petaflops, or 200,000 trillion calculations per second. That makes it about eight times more powerful than Titan, its predecessor, which was once the world’s fastest.

Summit delivered a record 148.6 petaflops on a benchmark test called High Performance Linpack, or HPL, a TOP500 press release said Monday. That was a slight improvement from six months ago, when Summit scored 143.5 petaflops. Summit debuted at 122.3 petaflops in June 2018.