Design of the IBM z15 microprocessor

The latest-generation IBM Z processor provides enhanced performance and compute capacity compared to its IBM z14 predecessor. This article describes some of the major improvements in both process and design including out-of-order load-and-store sequencing, single-instruction multiple-data and floating point enhancements, a new modulo arithmetic engine for accelerating elliptic curve cryptography, a hardware sort accelerator, and a workflow that modernized the development of these features. Outside of the central processing unit (CPU), the cache sizes have increased on all levels, and each processor chip now contains 12 CPUs. System topology changes have been introduced allowing up to five drawers to exist in a fully populated system. The processor cache subsystem includes numerous improvements in the area of fetch, store, and cache management policies aimed at speeding up both traditional data serving workloads and highly virtualized environments alike.