(第4空)Cloud computing is a phrase used to describe a variety of computing concepts that involve a large number of computers ( ) through a real-time communication network such as the Internet. In science, cloud computing is a ( ) for distributed computing over a network, and means the ( ) 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 ( ) for building the platform layer of the cloud. In turn, the platform layer is a foundation for implementing the ( ) layer for SaaS applications.