Based on the package offered by the vendors, cloud computing contains three different types of service models: software-as-aservice (SaaS), platform-as-a-service (PaaS), and infrastructure-asa-service (IaaS). SaaS allows clients to use providers' applications that run on a cloud infrastructure, which can be accessed through a web browser. All needed cloud infrastructure (such as network, servers, operating systems, and application software) is hosted in vendor's house. PaaS accommodates to developers' need by offering the entire computing platform and solutions set for an application needed at client's house. PaaS allows the client to control the application software (analysis and design), however, the developer must know how to work with vendors' programming languages, interfaces and database systems. IaaS offers clients the capabilities of processing, storage, networks, and other computing resources so they can run selective software (operating systems and applications) in house. Its only tradeoff is that cloud providers manage the infrastructure in use.