Cloud computing (on-demand computing)

Cloud computing is a kind of Internet-based computing, where shared resources,data and information are provided to computers and other devices on-demand. Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications and services) that can be rapidly provisioned and released with minimal management effort.
The term cloud has been used to refer to platforms for distributed computing. The old programs that drew network schematics surrounded the icons for servers with a circle, and a cluster of servers in a network diagram had several overlapping circles, which resembled a cloud.
Cloud computing, or in simpler shorthand just "the cloud", also focuses on maximizing the effectiveness of the shared resources. Cloud resources are usually not only shared by multiple users but are also dynamically reallocated per demand. This can work for allocating resources to users. For example, a cloud computer facility that serves European users during European business hours with a specific application (e.g., email) may reallocate the same resources to serve North American users during North America's business hours with a different application (e.g., a web server). This approach helps maximize the use of computing power while reducing the overall cost of resources by using less power, air conditioning, rack space, etc. to maintain the system. With cloud computing, multiple users can access a single server to retrieve and update their data without purchasing licenses for different applications.
Cloud computing has now become a highly demanded service or utility due to the advantages of high computing power, cheap cost of services, high performance, scalability, accessibility as well as availability
Cloud computing is the result of the evolution and adoption of existing technologies and paradigms. The goal of cloud computing is to allow users to take benefit from all of these technologies, without the need for deep knowledge about or expertise with each one of them.
The National Institute of Standards and Technology's definition of cloud computing identifies "five essential characteristics":
On-demand self-service.
A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with each service provider.
Broad network access.
Capabilities are available over the network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, tablets, laptops, and workstations).
Resource pooling.
The provider's computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand.
Rapid elasticity.
Capabilities can be elastically provisioned and released, in some cases automatically, to scale rapidly outward and inward commensurate with demand. To the consumer, the capabilities available for provisioning often appear unlimited and can be appropriated in any quantity at any time.
Measured service.
Cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts).

Cloud computing types
Private cloud
Private cloud is cloud infrastructure operated solely for a single organization, whether managed internally or by a third-party, and hosted either internally or externally
Public cloud
A cloud is called a "public cloud" when the services are rendered over a network that is open for public use. Public cloud services may be free
Hybrid cloud
Hybrid cloud is a composition of two or more clouds (private, community or public) that remain distinct entities but are bound together, offering the benefits of multiple deployment models. A hybrid cloud service as a cloud computing service that is composed of some combination of private, public and community cloud services, from different service providers
The specialized model of hybrid cloud, which is built atop heterogeneous hardware, is called "Cross-platform Hybrid Cloud". A cross-platform hybrid cloud is usually powered by different CPU architectures, for example, x86-64 and ARM, underneath. Users can transparently deploy applications without knowledge of the cloud's hardware diversity.[84] This kind of cloud emerges from the raise of ARM-based system-on-chip for server-class computing.
Others
Community cloud
Community cloud shares infrastructure between several organizations from a specific community with common concerns (security, compliance, jurisdiction, etc.), whether managed internally or by a third-party, and either hosted internally or externally.
Distributed cloud
A cloud computing platform can be assembled from a distributed set of machines in different locations, connected to a single network or hub service. It is possible to distinguish between two types of distributed clouds: public-resource computing and volunteer cloud.
Public-resource computing: This type of distributed cloud results from an expansive definition of cloud computing, because they are more akin to distributed computing than cloud computing.
Volunteer cloud: Volunteer cloud computing is characterized as the intersection of public-resource computing and cloud computing, where a cloud computing infrastructure is built using volunteered resources.
Intercloud
The Intercloud is an interconnected global "cloud of clouds and an extension of the Internet "network of networks" on which it is based.
Multicloud
Multicloud is the use of multiple cloud computing services in a single heterogeneous architecture to reduce reliance on single vendors, increase flexibility through choice, mitigate against disasters, etc.
It differs from hybrid cloud in that it refers to multiple cloud services, rather than multiple deployment modes (public, private, legacy)
Teleconferencing
A teleconference is a telephone meeting among two or more participants involving technology more sophisticated than a simple two-way phone connection. At its simplest, a teleconference can be an audio conference with one or both ends of the conference sharing a speaker phone. A teleconference or teleseminar is the live exchange and mass articulation of information among several persons and machines remote from one another but linked by a telecommunications system. Terms such as audio conferencing, telephone conferencing and phone conferencing are also sometimes used to refer to teleconferencing.
Audio Conferencing
Audio conferencing is the use of voice communications equipments to establish an audio link between geographically dispersed persons, one that allows them to conduct a conference. The conference call was the first form of audit conferencing and is still in use. Some firms install more elaborate systems consisting of private, high-quality audio communications circuits that can be activated with the flip of a switch.Audio conferencing does not require a computer. It only requires a two-way audio communications facility.
Audio conferencing is best suited for firms that are spread over a wide area.
Video Conferencing:
Video conferencing is the use of television equipment to link geographically dispersed conference participants. The equipment provides both sound and picture. Like audio conferencing, video conferencing also does not necessarily require a computer. With video conferencing, participants can see and hear each other. Generally, participants gather in relatively expensive, specially equipped rooms that can handle the complexities of simultaneous video and audio transmission.
There are three possible video conferencing configurations.
One-Way Video and Audio: Video and audio signals are sent from a single transmitting site to one or more receiving sites. This is a good way far a project leader to disseminate information to team members at remote locations.
One-Way Video and Two-Way Audio: People at the receiving sites can talk to people at the transmitting site, while everyone views the same video images.
Two-Way Video and Audio: The video and audio communications between all, sites are two-way. Although this is the most effective of the, electronically aided conferencing approaches, it can be the most expensive as well.
Computer Conferencing
A third form of electronic conferencing is computer conferencing. There is a fine line between this system and E-mail. Both use the same software and hardware. Two factors determine this application, who uses the system, and the subject matter.
E-mail is available to any one who has access to the network and that includes practically everyone in the office. Also, the E-mail system can be used for any purpose. Computer conferencing, on the other hand, is the use of a networked computer that allows particular task. Computer conferencing is more disciplined form of E-mail.Computer conferencing differs from audio and video conferencing because it can be used within a single geographic site. A person can use computer conferencing to communicate with someone in the office next door.