Roadrunner An Overview of Its Architecture

On Memorial Day of 2008, the Roadrunner supercomputer broke records worldwide and exceeded a sustained speed of one petaflop per second—one million billion calculations per second. Developed by IBM in collaboration with Los Alamos National Laboratory and the National Nuclear Security Administration, Roadrunner was designed for advanced physics and predictive simulations in a classified environment.

To take VPIC to a new level, Los Alamos scientists adapted the computer code to run on Roadrunner. Roadrunner consists of 18 "connected units." Each connected unit consists of 180 "triblade" computer nodes, all of which perform calculations in parallel. Roadrunner is a hybrid supercomputer because each computer node is built with two different types of microprocessors: (1) the Opteron microprocessor and (2) the enhanced Cell Broadband Engine, or "Cell."

Roadrunner

Each computer node includes four Opteron microprocessors and four enhanced Cells. An enhanced Cell accelerates each Opteron. The Opteron is the workhorse of many conventional supercomputers, whereas the enhanced Cell was specifically modified for use in Roadrunner. The original Cell's applications included rendering detailed graphics in real time for a video-game controller—a task mathematically similar to those involved in large-scale scientific simulations.

An enhanced Cell boosts the speed at which an Opteron processes data by as much as 25 times. However, to run at top speed on Roadrunner, a code such as VPIC must be modified carefully so that it can run optimally within Roadrunner's fairly unique hybrid architecture.

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