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 communication 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 infrastructure 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 infrastructure layer serves as the(74)for building the platform layer of the cloud. In turn,the platform layer is a foundation for implementing the(75)layer for SaaS applications.