The Perlmutter machine will be delivered to NERSC/LBNL in 2020 and will contain a mixture of CPU-only and GPU-accelerated nodes. Perlmutter will be a pre-exascale machine and contain a mixture of AMD EPYC CPU- only and NVIDIA Tesla GPU-accelerated nodes. In this talk we will describe the architecture of the machine and the analysis we performed in order to optimize this design to meet the needs of the ECP and NERSC user communities.