astructure that supports them. It is a general concept that incorporates software as a service, Web 2.0 and other recent, well-known technology trends, where the common theme is reliance on the Internet for satisfying the computing needs of the users. For example, Google Apps provides common business applications online that are accessed from a web browser, while the software and data is stored on the servers.Cloud computing is often confused with grid computing (a form of distributed computing whereby a "super and virtual computer" is composed of a cluster of networked, loosely-coupled computers, acting in concert to perform very large tasks), utility computing (the packaging of computing resources, such as computation and storage, as a metered service similar to a traditional public utility such as electricity) and autonomic computing (computer systems capable of self-management). Indeed many cloud computing deployments are today powered by grids, have autonomic characteristics and are billed like utilities, but cloud computing is rather a natural next step from the grid-utility model. Some successful cloud architectures have little or no centralised infrastructure or billing systems whatsoever including Peer to peer networks like BitTorrent and Skype and Volunteer computing like http://en.wikipedia.org/wiki/SETI@home.
The majority of cloud computing infrastructure currently consists of reliable servi
ces delivered through next-generation data centers that are built on compute and storage virtualization technologies. The services are accessible anywhere in the world, with The Cloud appearing as a single point of access for all the computing needs of consumers. Commercial offerings need to meet the quality of service requirements of customers and typically offer service level agreements. Open standards and open source software are also critical to the growth of cloud computing.As customers generally do not own the infrastructure, they are merely accessing or renting, they can forego capital expenditure and consume resources as a service, paying instead for what they use. Many cloud computing offerings have adopted the utility computing model which is analogous to how traditional utilities like electricity are consumed, while others are billed on a subscription basis. By sharing "perishable and intangible" computing power between multiple tenants, utilization rates can be improved (as servers are not left idle) which can reduce costs significantly while increasing the speed of application development. A side effect of this approach is that "computer capacity rises dramatically" as customers do not have to engineer for peak loads. Adoption has been enabled by "increased high-speed bandwidth" which makes it possible to receive the same response times from centralized infrastructure at other sites.
The cloud computing "revolution" is being driven by companies like Amazon, Google, Salesforce and Yahoo! as well as traditional vendors including Hewlett Packard, IBM, Intel and Microsoft and adopted by individuals through large enterprises including General Electric, L'Oréal, Procter & Gamble and Valeo.
The History of Cloud Computing.
The Cloud is a metaphor for the Internet, derived from its common depiction in network diagrams (or more generally components which are managed by others) as a cloud outline.
The underlying concept dates back to 1960 when John McCarthy opined that "computation may someday be organized as a public utility" (indeed it shares characteristics with service bureaus which date back to the 1960s) and the term cloud was already in commercial use in the early 1990s to refer to large ATM networks . By the turn of the 21st century, cloud computing solutions had started to appear on the market , though most of the focus at this time was on Software as a service.
Amazon.com played a key role in the development of cloud computing by modernizing their data centers after the dot-com bubble and (having found the new cloud architecture resulted in significant internal efficiency improvements) providing access to their systems by way of Amazon Web Services in 2002 on a utility computing basis.
2007 saw increased activity, including Google, IBM and a number of universities embarking on a large scale cloud computing research project, around the time the term started gaining popularity in the mainstream press. It was a hot topic by mid-2008 and numerous cloud computing events had been scheduled.
In August 2008 Gartner observed that "organisations are switching from company-owned hardware and software assets to per-use service-based models" and that the "projected shift to cloud computing will result in dramatic growth in IT products in some areas and in significant reductions in other areas".
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