Cloud computing is location independent computing, whereby shared servers provide resources, software, and data to computers and other devices on demand, as with the electricity grid. Cloud computing is a natural evolution of the widespread adoption of virtualization, service-oriented architecture and utility computing. Details are abstracted from consumers, who no longer have need for expertise in, or control over, the technology infrastructure "in the cloud" that supports them.
Cloud computing describes a new supplement, consumption, and delivery model forIT services based on the Internet, and it typically involves over-the-Internet provision of dynamically scalable and often virtualized resources. It is a byproduct and consequence of the ease-of-access to remote computing sites provided by the Internet.This frequently takes the form of web-based tools or applications that users can access and use through a web browser as if it were a program installed locally on their own computer.
The National Institute of Standards and Technology (NIST) provides a somewhat more objective and specific definition here. 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. Typical cloud computing providers deliver common business applications online that are accessed from another Web service or software like a Web browser, while the software and data are stored on servers.
Most cloud computing infrastructures consist of services delivered through common centers and built on servers. Clouds often appear as single points of access for consumers' computing needs. Commercial offerings are generally expected to meet quality of service (QoS) requirements of customers, and typically include service level agreements (SLAs). The major cloud service providers include Amazon,Rackspace Cloud, Salesforce, Skytap, Microsoft and Google. Some of the larger IT firms that are actively involved in cloud computing are Huawei, Cisco, Fujitsu, Dell, Red Hat, Hewlett Packard, IBM, VMware, Hitachi and NetApp.
credit : http://en.wikipedia.org
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