IBM was picked from five bidders because its costs were lower and it provided a better "risk reduction plan" -- essentially a backup plan if something goes wrong, Seager said. He declined to name the losing bidders but said it was a close contest.

The price tag for the system won't be disclosed until a later date, but such computers can easily run into hundreds of millions of dollars.

Besides managing nuclear weapons, Sequoia will be used for research into astronomy, energy, the human genome and climate change, IBM said. The system will allow forecasters to predict local weather events that are less than 1 kilometer across, it said, compared to 10 kilometers today.

While it is being built, Lawrence Livermore will use a smaller IBM supercomputer called Dawn to develop the weapons applications that will run on Sequoia. Dawn will be operational in the coming months and perform at 500 teraflops.

It's not certain that Sequoia will be the most powerful supercomputer in the world by the time it goes into operation, but Turek sounded confident that it will be.