Cloud Computing term was derived from the symbol of “Cloud” which is often used to represent the “Internet” in the flowcharts and diagrams. It represents anything that involves delivering Hosted Services over the Internet.

Characteristics of Cloud Computing:

Cloud computing has three basic characteristics which distinguish it from traditional hosting.

• It is sold only on demand. It may be by the minute or hour.

• Provider manages the service completely.

• User can use as much capacity of services as needed, in a given time.

Deployment Models

A cloud may be “Public “ or “Private” .

1. Public Cloud:

A Public cloud sells offers to every one on the Internet. Service provider provides services to general public. These services may be offered on a pay per use model or free.

2. Private Cloud:

When cloud services are offered for any special organization or to limited persons, it is known as Private Cloud. User has to buy and manage the services himself. That’s why it is not so popular.

3. Hybrid Cloud:

It may be defined as composition of two clouds. In Hybrid cloud, entities to be combined remain the same but bound together to get the benefits of multiple deploying models. It lacks flexibility and security but provides fault tolerance for in-house-applications.

Categories of Services of Cloud Computing:

Cloud services are divided into three categories.

• Infrastructure as a Service:

Infrastructure as a Service is the model in which service provider owns the equipment and is responsible for the hosting, maintaining and running it. The payment is made on a Per use basis . Client can ask for more services online as soon as required. As payment is made on per use basis, it is also known as Utility Computing . Sometimes Infrastructure as a Service is referred to as Hardware as a Service.

• Platform as a Service:

Platform as a Service is the model of cloud in which applications are developed on the Platform of the provider over the Internet. Service providers use Websites, Gateways or Portals installed on customer’s computer to provide services. Platform as a service is cost effective as different infrastructure services are used from a single vendor rather than maintaining multiple hardware facilities.

• Software as a Service:

In this cloud model Application Software is installed and operated in the cloud and cloud users access this software from the cloud clients. Both, the Application and Data is hosted by the provider which enables user to access services form anywhere over the Internet.