For the fourth consecutive time, Tianhe-2, developed by China's National University of Defense Technology, has retained the top spot as the world's fastest supercomputer, according to a biannual Top500 list of supercomputers released here on Monday.

The updated list came on the heels of an announcement Friday by the US Department of Energy (DOE) that it will spend 325 million US dollars on building two supercomputers, which will be three to five times faster than Tianhe-2.

Although the United States clearly wants to regain the supercomputing crown from China, Jack Dongarra, professor of the University of Tennessee and Top500 editor, insisted that there is no connection between the two announcements.

"The (US) systems will be operational in 2018. It's just a coincidence," Dongarra wrote in an email to Xinhua, adding that there will be additional announcements to come from the DOE.

And before that, there will be no machine that can dethrone the Chinese supercomputer, he said.

Tianhe-2, which means "Milky Way-2" in Chinese, can operate at 33.86 petaflops per second (Pflop/s), the equivalent of 33,860 quadrillion calculations per second.

The National Supercomputer Center in Guangzhou in south China, where Tianhe-2 is installed, is reportedly making an update to increase the system's speed to more than 100 Pflop/s.

Titan, installed at the DOE's Oak Ridge National Laboratory, remains the No. 2 system with a performance of 17.59 Pflop/s. Sequoia, installed at the DOE's Lawrence Livermore National Laboratory, is again the No. 3 system with a performance of 17.17 Pflop/s.

Japan's K computer is the No. 4 system with 10.51 Pflop/s, followed by Mira, installed at the DOE's Argonne National Laboratory, which has a performance of 8.59 Pflop/s.

In fact, the top10 list was almost the same as the one published six months ago. The only new entry was at number 10, a 3.57 Pflop/s Cray Storm system installed at an undisclosed US government site.

"These machines in the top10 are very expensive and provide extreme computing power. Perhaps we have enough computing power for the moment and not enough funding for the next generation just now," Dongarra said, noting that the interest and need by science for these systems and more powerful systems will not end.

In terms of overall systems, the United States remains the top country with 231, but this number is down from 233 in June 2014 and down from 265 on the November 2013 list, nearing the country's historical low number on the list.

China still occupies the No. 2 position as a user of supercomputers, ahead of Japan, Britain, France, and Germany. But the number of systems installed in the Chinese mainland has fallen to 61, compared with 76 on the previous list.

The Top500 list is considered one of the most authoritative rankings of the world's supercomputers. It is compiled on the basis of the machines' performance on the Linpack benchmark by experts from the United States and Germany.