"The fact that non-U.S. vendor like NEC had the fastest computer was seen as a big challenge for U.S. computer industry," said Horst Simon, director of the supercomputing center at Lawrence Berkeley National Lab in California.
"That an American vendor and an American application has won back the No. 1 spot — that's the main significance of this."
Earth Simulator can sustain speeds of 35.86 teraflops.
IBM said its still-unfinished BlueGene/L System, named for its ability to model the folding of human proteins, can sustain speeds of 36 teraflops. A teraflop is 1 trillion calculations per second.