Cloud computing is a phrase used to describe a variety of computing concepts that involve a large number of computers (71) through a real-time commutinication network such as the Internet. In science, cloud computing is a (72) for distributed computing over a network, and means the (73) to run a program or application on many connected computers at the same time. The architecture of a cloud is developed at three layers: infrastructure, platform, and application.The infrastucture layer is built with virtualized compute,storage,and network resources. The platform layer is for general-purpose and repeated usage of the collection of software resources. The application layer is formed with a collection of all needed software modules for SaaS applications. The infrastucture layer serves as the (74) for building the platform layer of the cloud. In turn,the platform layer is foundation for implementing the (75) layer for SaaS application.