Scientists want faster, more powerful high-performance supercomputers to simulate complex physical, biological, and socioeconomic systems with greater realism and predictive power. In May, Los Alamos scientists doubled the processing speed of the previously fastest computer. Roadrunner, a new hybrid supercomputer, uses a video game chip to propel performance to petaflop/s speeds capable of more than a thousand trillion calculations per second. "The computer is a speed demon. It will allow us to solve tremendous problems," said Thomas D'Agostino, head of the National Nuclear Security Administration, which oversees nuclear weapons research and maintains the warhead stockpile. The computer might also have many medical and science applications, including developing biofuels or discovering drug therapies. Modern supercomputers have thousands of identical computer nodes, each containing a microprocessor and a separate memory. The nodes are connected to form a cluster and work simultaneously on a single problem.A huge obstacle to increased performance is the memory barrier. In the not-too-distant past, the time to fetch data from the node memory and load it into the processing units (called the "compute core") of a microprocessor was comparable to the time it would take that core to do the number crunching. Now the number crunching is 50 times faster than the time to fetch and load data. The time spent in data retrieval and communications can no longer be ignored. Clearly, the old solution for increasing supercomputer performance—miniaturizing circuits and using faster clocks—is breaking down. "We replace our high-performance supercomputers every four or five years," says Andy White, leader of supercomputer development at Los Alamos. "They become outdated in terms of speed, and the maintenance costs and failure rates get too high." In 2002, when Los Alamos scientists were planning for their next-generation supercomputer, they looked at the commodity market for a way to make an end run around the speed and memory barriers looming in the future. What they found was a joint project by Sony Computer Entertainment, Toshiba, and IBM to develop a specialized microprocessor that could revolutionize computer games and consumer electronics, as well as scientific computing.
Roadrunner is a cluster of approximately 3,250 compute nodes interconnected by an off-the-shelf parallel-computing network. Each compute node consists of two AMD Opteron dual-core microprocessors, with each of the Opteron cores internally attached to one of four enhanced Cell microprocessors. This enhanced Cell does double-precision arithmetic faster and can access more memory than can the original Cell in a PlayStation 3. The entire machine will have almost 13,000 Cells and half as many dual-core Opterons.