Sequoia will occupy 96 server racks over an area a bit larger than a tennis court. IBM won't discuss the machine in detail because it is still being developed, but Dave Turek, vice president of IBM's Deep Computing initiative, said it will be similar in design to its predecessor, Blue Gene/P, but on a much larger scale. The system will run a version of the Linux OS, use IBM's embedded Power processors and have 1.6 petabytes of main memory.

Because a computer this size has never been built, scaling the processor count, memory DIMMs and management subsystems comes with a level of uncertainty, Turek acknowleged. "This is not an exercise for the faint of heart," he said "When you push the limits of scalability you start to observe problems that were simply unanticipated."

Among IBM's challenges will be how to scale the management subsystems to automate as many tasks as possible, and to allow administrators to keep track of workloads and make the right choices during operation.

Lawrence Livermore will have to write applications that can take advantage of such a massively parallel system. It chose IBM's embedded processors because they are "easier to deal with on our complicated weapons code" than the Cell processors used for Roadrunner, Seager said.

Sequoia will be far more energy efficient than a Blue Gene/P system, according to Turek, but because of its size Lawrence Livermore will still have to double the power supply to its computing center. Sequoia will require 6 megawatts of power, compared to 1.8 megawatts for ASC Purple, Seager said.