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| Active | Since 2018[1] |
|---|---|
| Operators | National Nuclear Security Administration |
| Location | Lawrence Livermore National Laboratory |
| Architecture | IBMPOWER9 CPUs NvidiaTesla V100 GPUs Mellanox EDRInfiniBand[2] |
| Power | 11MW |
| Operating system | Red Hat Enterprise Linux[3] |
| Memory | 2–2.4 PiB[1] |
| Speed | 125petaflops (peak)[2] |
| Ranking | TOP500: 20, June 2025 |
| Purpose | Nuclear weapon simulations[4] |
| Website | hpc |
Sierra orATS-2 is asupercomputer built for theLawrence Livermore National Laboratory for use by theNational Nuclear Security Administration as the second Advanced Technology System. It is primarily used for predictive applications in nuclear weaponstockpile stewardship, helping to assure the safety, reliability, and effectiveness of the United States' nuclear weapons.
Sierra is very similar in architecture to theSummit supercomputer built for theOak Ridge National Laboratory. The nodes in Sierra are Witherspoon IBM S922LCOpenPOWER servers with two GPUs per CPU and four GPUs per node. These nodes are connected with EDRInfiniBand. In 2019 Sierra was upgraded withIBM Power System AC922 nodes.[5][6]
Sierra is composed of 4,474 nodes, 4,284 of which are compute nodes. Each node has 256GB of RAM, 44IBMPOWER9 cores spread across two physical sockets, and FourNvidia Tesla V100 GPUs, each providing 16GB of VRAM. This gives the complete system 8,948 CPUs, 17,896 GPUs, 1.14 PB of RAM, and 286 TB of VRAM.[7]
Sierra has consistently appeared on theTop500 list, peaking at second place in November 2018.[8] As of November 2023, it is in tenth place.[9] Only 4.6 petaflops of its performance come from its CPUs, with the large majority (120.9 petaflops) coming from the Tesla GPUs.[7]