ExCALIBUR - U.K.'s Preparation for the Arrival of the Next Generation of HPC

The articles in this special section focus on the ExCalibur high performance computing program. In n 2019, the U.K. Government funded the Exascale Computing Algorithms and Infrastructures Benefitting UK Research (ExCALIBUR) Programa with an investment of £45.7m, led by the Met Office and EPSRC along with other U.K. research bodies. The vision of ExCALIBUR is to prepare the U.K. hardware and software landscape for the emerging age of exascale computing. The ExCALIBUR priorities are as follows: 1) Separation of Concerns, 2) Co-Design, 3) Data Science, and 4) Investing in People. In 2020, in the first round of ExCALIBUR, 10 software Design and Development Working Groups (DDWG) were formed, each representing a different community and tasked with developing high-priority use cases, the cost-effective strategy to enable these, and demonstrate collaborative progress toward the successful transition to exascale. Significant funds have been invested in 2021 to support a number of these DDWGs for a further three years with some of the DDWGs combining their efforts after identifying common possible solutions to remove underlying bottlenecks in their different applications. These longer three-year projects will see substantial software and other outputs, benefiting the international HPC community. In terms of hardware, the U.K