The IBM® POWER9™ processor is a superscalar symmetric multiprocessor designed for use in servers and large-cluster systems. It uses 14 nm technology with 17 metal layers. The POWER9 processor supports direct-attach memory. It supports a maximum symmetric multiprocessing (SMP) size of two sockets and is targeted for scale-out workloads. This user’s manual describes the POWER9 processor and provides information about the registers, facilities, initialization, and use of the POWER9 processor. This document focuses primarily on the microprocessor core and the storage subsystem.