This document discusses cloud computing architectures and service-oriented architectures. It describes two types of virtualization architectures - virtualization as the operating system and virtualization with a host operating system. It also discusses multi-tenancy architecture, where multiple users share resources for efficiency, and security needs to be ensured at all levels. Finally, it defines service-oriented architecture as an architectural style using services that communicate with each other, and notes that cloud computing is built on service-oriented architecture principles with services communicating via web services.