According to the Top 500 site listing the world's fastest computers, the current number-crunching champ is China's 93-petaflops Sunway TaihuLight, followed by its Tianhe-2, coming in at 34 petaflops. Japan's most powerful system at the moment is a 13.5 petaflops machine. Overall, Japan has the fourth-largest number of supercomputers in the Top 500 listing, after the US, China, and Germany.
top 500 list
Top US iat number 3, a Cray XK7 with 560,640 cores
3 DOE/SC/Oak Ridge National Laboratory
United States Titan - Cray XK7 , Opteron 6274 16C 2.200GHz, Cray Gemini interconnect, NVIDIA K20x
Cray Inc.