The IBM POWER9 processor is the latest Reduced Instruction Set Computer microprocessor from IBM. POWER9 employs a new modular core microarchitecture to counter the technology trend of decreasing frequency and increasing power density from generation to generation. The new POWER9 design enables a family of processors optimized for a broad range of server applications. The new microarchitecture is closely coupled with a rich set of new instructions geared toward data-centric applications. In this paper, we describe the POWER9 core microarchitecture innovations, its new instructions and features, and the exploitation of this new design for computing in the cognitive era.