Power and cost aren’t the only problems preventing practical exascale systems. The risk of hardware failures grows as new supercomputers pack in a greater number of components, says Bronis de Supinski, chief technical officer for Livermore Computing at Lawrence Livermore National Laboratory, in California. His lab’s IBM Blue Gene/Q supercomputer, named Sequoia, currently has a mean time between failures of 3.5 to 7 days. Such a window could shrink to just 30 minutes for an exascale system.