Road to Exascale Computers

Exascale computers, which would be 1000 times more powerful than today's fastest supercomputers, will need to have optics playing a bigger role, said Jeffrey Kash of IBM Research during a presentation at Frontiers in Optics 2009.

Kash, who said he was presenting his own views and not those of IBM Research, said that VCSEL-based optics have displaced electric cables today in supercomputers, but with power, density and cost requirements increasing exponentially as the systems get powerful, the need increases to move to on-chip optics.

The top supercomputer today is the IBM Roadrunner petascale floating point operations per second (petaflops) machine at Los Alamos National Laboratory in New Mexico, which became operational in 2008 contains 55 miles of active optic cables. To highlight the inroads optics has made recently in such computers, Kash pointed out that Japan's supercomputer, the NEC Earth Simulator, the fastest supercomputer in the world between 2002 and 2004, contained no optics, and the ASCI Purple machine installed at Lawrence Livermore National Lab in 2005 uses optics for longer links and copper for shorter ones.

Because a 10x increase in performance means the machine will consume double the power, to make future supercomputers feasible to build and to operate optics will need to be more widely used he said. In 2008 a 1-petaflop computer cost $150 million to build and consumes 2.5 MW of power. Using the same technology, by 2020 a 1 exaflop machine would cost $500 million to build and consume 20 MW of power.

Kash gave a timeline that would find optics replacing electrical backplanes by 2012 and replacing electrical printed circuit boards by 2016. In 2020, optics could be directly on the chip. In a less aggressive scenario, by 2020 all off-chip communications need to be optical, he said.

But for that to happen, to get optics up to millions of units in 2010, the price needs to drop to about $1 per Gb/s, he said. Today, Gb/s processing costs about $10.

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Melinda Rose
Senior Editor

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