Systems with millions of hundred-core processors would be difficult to maintain, and reliability is a big worry. New fault-tolerance methods will be required to make sure that the processing cores can all operate in conjunction. Some experts have suggested that an exascale supercomputer would bring back the heady days of the earliest vacuum tube computers – when one tube died, operators had to shut everything down, replace it and start over.
A future supercomputer processing many trillions of operations per second might only run for a few minutes before suffering an error and being forced to shut down. The solution to this problem may involve moving to more simplistic designs.
At Lawrence Livermore, we held one of the new computers for IBM's forthcoming Sequoia project in one hand. It's about half the size of a netbook PC, and there are no exposed wires. A demonstration of the IBM Dawn supercomputer – which will be installed this year as a precursor to Sequoia – showed that the design is ultra-simple: each computer is installed in a row, and the rows are installed in multiple racks. The picture only gets complicated with the interconnects, the storage and the simulation software programming.
"Simplicity in design is critical," says Seager. "An exascale supercomputer would likely have fewer parts than current-generation supercomputers. Today, an entire computer within Blue Gene/L has embedded DRAM, voltage regulatory modules and Gigabit Ethernet, but it's extremely simple."
Beyond exascale
Many questions remain when it comes to exascale computing, not least how much such a machine will cost to build. Flynn from Fusion-io says that it would cost millions of dollars just to run the virtual experiments on an exascale supercomputer, let alone the cost of producing the equipment itself. Current supercomputers cost up to $100million, and given the manufacturing scale required, an exascale supercomputer could cost 10 times as much. That would be a heavy investment to make.
Yet the march of science demands the progression of computing power to solve some of the most complex problems facing humankind – such as climate change and the cure for cancer. And what's beyond exascale? Believe it or not, zettaflop computing is already on the very distant – but just visible – horizon.
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