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Cloud computing is Internet-based computing, whereby shared resources, software, and

information are provided to computers and other devices on demand, like the electricity grid.

Cloud computing is a paradigm shift following the shift from mainframe to client–server in theearly 1980s. Details are abstracted from the users, who no longer have need for expertise in, or 

control over, the technology infrastructure "in the cloud" that supports them.[1]

 Cloud computingdescribes a new supplement, consumption, and delivery model for IT services based on the

Internet, and it typically involves over-the-Internet  provision of dynamically scalable and oftenvirtualized resources.[2][3] It is a byproduct and consequence of the ease-of-access to remote

computing sites provided by the Internet.[4] 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 installedlocally on their own computer.[5]  NIST provides a somewhat more objective and specific

definition here.[6] 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 ,[7] and later to depict the Internet incomputer network diagrams as an abstraction of the underlying infrastructure it represents.[8]

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. A key element of cloud computing is customization and the creation of a

user-defined experience. 

Hybrid cloud

See also: Cloud storage gateway

A hybrid cloud environment consisting of multiple internal and/or external providers[61] "will be

typical for most enterprises".[62] By integrating multiple cloud services users may be able to easethe transition to public cloud services while avoiding issues such as PCI compliance.[63]

Another perspective on deploying a web application in the cloud is using Hybrid Web Hosting,where the hosting infrastructure is a mix between Cloud Hosting for the web server, and

Managed dedicated server for the database server.

The Intercloud[66]  is an interconnected global "cloud of clouds"[67][68] and an extension of the

Internet "network of networks" on which it is based. [69] The term was first used in the context of 

cloud computing in 2007 when Kevin Kelly stated that "eventually we'll have the intercloud, the

cloud of clouds. This Intercloud will have the dimensions of one machine comprising all servers

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and attendant cloudbooks on the planet.".[67] It became popular in 2009[70] and has also been used

to describe the datacenter of the future.[71]

The Intercloud scenario is based on the key concept that each single cloud does not have infinite physical resources. If a cloud saturates the computational and storage resources of its

virtualization infrastructure, it could not be able to satisfy further requests for service allocationssent from its clients. The Intercloud scenario aims to address such situation, and in theory, each

cloud can use the computational and storage resources of the virtualization infrastructures of other clouds. Such form of pay-for-use may introduce new business opportunities among cloud

 providers if they manage to go beyond theoretical framework. Nevertheless, the Intercloud raises

many more challenges than solutions concerning cloud federation, security, interoperability,QoS, vendor's lock-ins, trust, legal issues, monitoring and billing.[citation needed ]

The concept of a competitive utility computing market which combined many computer utilities

together was originally described by Douglas Parkhill in his 1966 book, the "Challenge of the

Computer Utility". This concept has been subsequently used many times over the last 40 years

and is identical to the Intercloud.

Grid computing is a term referring to the combination of computer resources from multipleadministrative domains to reach common goal. What distinguishes grid computing fromconventional high performance computing systems such as cluster computing is that gridstend to be more loosely coupled, heterogeneous, and geographically dispersed. Although agrid can be dedicated to a specialized application, it is more common that a single grid willbe used for a variety of different purposes. Grids are often constructed with the aid of general-purpose grid software libraries known as middleware.

“Distributed” or “grid” computing in general is a special type of  parallel computing that relies oncomplete computers (with onboard CPUs, storage, power supplies, network interfaces, etc.)

connected to a network (private, public or the Internet) by a conventional network interface, such

as Ethernet. This is in contrast to the traditional notion of a supercomputer , which has many processors connected by a local high-speed computer bus.[citation needed ]

The primary advantage of distributed computing is that each node can be purchased as

commodity hardware, which, when combined, can produce a similar computing resource as

multiprocessor  supercomputer, but at a lower cost. This is due to the economies of scale of  producing commodity hardware, compared to the lower efficiency of designing and constructing

a small number of custom supercomputers. The primary performance disadvantage is that the

various processors and local storage areas do not have high-speed connections. This arrangement

is thus well-suited to applications in which multiple parallel computations can take placeindependently, without the need to communicate intermediate results between processors.[citation

needed ] The high-end scalability of geographically dispersed grids is generally favorable, due to the

low need for connectivity between nodes relative to the capacity of the public Internet.[citation