Supercomputers can be measured in several ways, but the vital statistic is their ability to perform floating-point operations per second, or flops. Flopping as fast as possible is what makes you successful. At her peak, Sierra could hit 94.64 petaflops—94.64 quadrillion floating-point operations—per second. El Capitan, at 1.809 exaflops, is about 19 times faster. In late 2025, he was officially declared the world’s fastest supercomputer. Sierra’s juice, Neely says, was no longer worth the squeeze.
There was no big red button, no giant lever, that turned Sierra off. Someone could’ve just cut the cords, sure, but that’s not the recommended procedure. First, Sierra’s user scientists were warned, via email, to save their work. Then a DNR was formally instituted—no new parts.
The decommissioning proceeded in phases, starting with the compute nodes and the rack switches—management nodes are last, since they’re needed until the very end. The process involves running scripts that, digitally, shut the computer down, and then hard power switches are flipped off too. There’s also a dehydration. When she was alive, Sierra could get quite hot, so the lab recirculated thousands of gallons of water per minute, funneled through veiny pipes that came up from under her floorboards. As she approached death, that water had to be drained. It was tested by safety staff first, to ensure it was an environmentally healthy pH.
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