This document defines and explains cloud computing. Cloud computing refers to storing and accessing data and programs over the Internet instead of a computer's hard drive. It discusses the history of cloud computing beginning in the 1950s. The key components of cloud computing are clients, distributed servers located in data centers, and a central server that administers the system. There are different service models depending on what is provided via the cloud. Cloud services can be deployed in public, private, community, or hybrid models. The popularity of cloud computing is due to reduced complexity, scalability, and not needing to purchase software licenses.