Last year, Japan fired up an ultrafast computer that puts its closest competitors to shame. What will it take for the United States to catch up?

Even in a field defined by continuous breakthroughs, the achievement was a shocker: last March the Japanese government fired up a computer that soon proved to be the fastest in the world, in some cases outperforming the next-fastest computer by a factor of 10. The Earth Simulator, built by NEC, took four years to assemble and cost at least $350 million. It quickly delivered real-world scientific results in global-climate modeling, completing simulations that made other computers look crude.