While there are many important systems in high performance computing (HPC) available today, the HPC community lacks a single reference on the key aspects of the systems, such as application workloads, procurement timeline, and facilities specification. This book provides the first comprehensive resource to describe these systems and their hardware and software architectures. The first part of the book explores current trends in HPC. The second part presents detailed descriptions of deployed systems that span a number of architectures, application workloads, facilities, and sponsors.