El Capitan Supercomputer Detailed: AMD CPUs & GPUs To Drive 2 Exaflops of Compute

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Back in August, the United States Department of Energy and Cray announced plans for a third United States exascale supercomputer, El Capitan. Scheduled to be installed in Lawrence Livermore National Laboratory (LLNL) in early 2023, the system is intended primarily (but not exclusively) for use by the National Nuclear Security Administration (NNSA), who uses supercomputers in their ongoing nuclear weapons modeling. At the time the system was announced, The DOE and LLNL confirmed that they would be buying a Shasta system from Cray (now part of HPE), however the announcement at the time didn’t go into any detail about what hardware would actually be filling one of Cray’s very flexible supercomputers.

But as of today, the wait is over. This afternoon the DOE and HPE are announcing the architectural details of the supercomputer, revealing that AMD will be providing both the CPUs and accelerators (GPUs), as well as revising the performance estimate for the supercomputer. Already expected to be the fastest of the US’s exascale systems, El Capitan was originally commissioned as a 1.5 exaflop system seven months ago. However thanks to some late configuration changes, the DOE now expects the system to reach 2 exaflops once it’s fully installed, which would cement its place at the top of the US’s supercomputer inventory.

Overall, El Capitan is the second (and apparently final) system being built as part of the US DOE’s CORAL-2 program for supercomputers. Like the similar Frontier system, El Capitan comes with a $600 million price tag and is intended to ensure the US’s leadership in supercomputers in the exascale era. LLNL will be using the system to replace Sierra, their current IBM Power 9 + NVIDIA Volta supercomputer. All told, El Capitan will be 16 times more powerful than the system it replaces. LLNL will be using it primary for nuclear weapons modeling – substituting for actual weapon testing – while the system will also see secondary use as a research system in other fields, particularly those where machine learning can be applied.

El Capitan is the second exascale supercomputer win for AMD, who is also providing the CPUs and GPUs behind the 1.5 exaflops Frontier system for Oak Ridge National Laboratory. And indeed, at a high level El Capitan looks a whole lot like Frontier from a hardware perspective. With Cray serving as the prime contractor on both systems, El Capitan and Frontier are Cray Shasta systems, employing AMD’s processors along with Cray’s cabinets and their Slingshot interconnect technology. However in an interesting turn of events, LLNL is being just a bit more forthcoming about what specific hardware will be in their new supercomputer.

On the CPU side of matters, AMD will be supplying a standard version of their Zen 4-based “Genoa” EPYC processor. As it’s still two generations out from AMD’s current wares, the amount of information on Zen 4/Genoa is limited, but AMD is promising support for next-generation memory, Infinity Fabric 3, as well as broad promises of both single and multi-threaded performance leadership. Notably, this is a greater level of detail on the CPU than we currently have for Frontier, which is using an unspecified and customized next-generation EPYC CPU.
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