This chapter examines the hardware building blocks essential to warehouse-scale computers (WSCs), detailing system design principles and key tradeoffs between scale-out and scale-up architectures. It explores WSC server and rack design, including the evolution from monolithic to disaggregated systems. Special emphasis is placed on the increasing importance of specialized accelerators, with in-depth analyses of machine learning accelerators like TPUs and GPUs, as well as video acceleration with VCUs. The discussion extends to networking, covering host networking, smartNICs, cluster networking, and WANs, and highlights innovations such as spine-less networking and optical switching. The chapter further delves into the varied storage needs of WSCs, discussing HDD and SSD characteristics and the trend toward disaggregated storage designs. Finally, it concludes with an overview of cross-cutting issues and a historical review of WSC design for servers, storage, and networking over the past twenty-five years.