This document discusses power provisioning for large computer systems like data centers. It first shows the hierarchy for distributing power in a data center and issues that can lead to inefficient power usage like staged deployments and variable loads. It then analyzes the power usage profiles of different server components and workloads like web search, finding that actual peak power often differs from nameplate ratings. Finally, it explores approaches for improving power efficiency, such as CPU voltage/frequency scaling and reducing idle power consumption.