The choice of Arm certainly makes sense, given its European roots in the UK, and its commercial licensing scheme. Anyone can buy an Arm license and develop a processor of their own design, something not possible with Intel, AMD, or NVIDIA technology. In some ways, RISC-V is even more attractive, since it’s offered as an open standard architecture that can be had at no cost under a BSD license, either for developing free implementations or proprietary designs.
It’s worth noting that the selection of Arm and RISC-V has not been officially announced. However, given inclination of some of the major European players — the long history of the Mont-Blanc exascale project with Arm (including its latest project to build an Arm-based SoC for exascale machines), BSC’s enthusiasm for RISC-V (it recently hosted the RISC-V Workshop), and Atos’s interest in both architectures — it’s hard to fathom any other choice. Of course, OpenPower and even MIPS are possibilities, but neither one has been the focus of any European HPC research. Coming up with a completely new processor architecture is the least likely option, given the timeframes for the pre-exascale and exascale deployments. […]