Cloud computing is Internet-based computing, whereby shared resources, software and information are provided to computers and other devices on-demand, like a public utility. It is a paradigm shift following the shift from mainframe to client-server that preceded it in the early ’80s. Details are abstracted from the users who no longer have need of, expertise in, or control over the technology infrastructure “in the cloud” that supports them. 1] Cloud computing describes a new supplement, consumption and delivery model for IT services based on the Internet, and it typically involves the provision of dynamically scalable and often virtualized resources as a service over the Internet.  It is a byproduct and consequence of the ease-of-access to remote computing sites provided by the Internet.  The term cloud is used as a metaphor for the Internet, based on the cloud drawing used in the past to represent the telephone network, and later to depict the Internet in computer network diagrams as an abstraction of the underlying infrastructure it represents. 6] Typical cloud computing providers deliver common business applications online which are accessed from another web service or software like a web browser, while the software and data are stored on servers. A technical definition is “a computing capability that provides an abstraction between the computing resource and its underlying technical architecture (e. g. , servers, storage, networks), enabling convenient, on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction.  This definition states that clouds have five essential characteristics: on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service.  The majority of cloud computing infrastructure, as of 2009[update], consists of reliable services delivered through data centers and built on servers. Clouds often appear as single points of access for all consumers’ computing needs. Commercial offerings are generally expected to meet quality of service (QoS) requirements of customers and typically offer SLAs.