View photo gallery: The new supercomputer uses graphic processing units as accelerators to achieve a maximum theoretical speed of 20 petaflops.

Oak Ridge National Laboratory has the fastest supercomputer in the world.

The lab’s Titan supercomputer topped the latest list of the world’s 500 fastest supercomputers for Nov. 2012. The Cray XK7 system reached 17.59 petaflops — that’s quadrillions of calculations per second. The machine has over half-a-million processors and over a quarter of a million NVIDIA K20x accelerator cores.

This past summer, Lawrence Livermore National Laboratory’s Sequoia system was named the fastest computer, giving the United States the opportunity to claim the fastest supercomputer mantle for the first time since 2009. Now, the U.S. occupies the top two slots on the Top 500 list.

Oak Ridge unveiled Titan late last month, claiming at the time that it would be named either the fastest or second-fastest high-performance computer in the world. Titan, which is Oak Ridge’s Jaguar system transformed, is different from Sequoia in that it is an open machine. This means researchers in both the public and private sector can use it to run experiments. Livermore’s Sequoia is a secure machine, used exclusively to manage the nation’s nuclear weapons stockpile.

Oak Ridge’s achievement is a realization of one of the president’s national security priorities: making the United States the top achiever in the high-performance computing world. In addition to supercomputing dominance, cybersecurity has been high on the president’s agenda. As The Post’s Ellen Nakashima reports, in mid-October the president signed a secret directive giving the U.S. military permission to act more aggressively in thwarting cyberattacks.

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