As you can appreciate Cloud Computing is really in its infancy and is therefore likely to change drastically over time. Cloud computing is basically computing service. In this computing service model, all the servers, networks, applications and other elements that are associated with data centers are made accessible to IT and end users via the Internet, in such a way that allows IT to acquire only the type and amount of computing services that they actually need. The cloud service model varies from traditional outsourcers in a way that customers do not turn over their own IT resources to be managed and controlled. Instead they plug into the “cloud” for infrastructure services, platform (operating system) services, or software services, treating the “cloud” much as they would treat an internal data center or computer performing the same functions, essentially as a service.

The main services provided by cloud computing service model can basically be divided into three main categories namely Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS).

Infrastructure-as-a-Service (IaaS) provides virtual servers with unique IP addresses. Also, it provides blocks of storage on demand. Customers benefit from an API from which they can control and manage their servers. Moreover, because of the economies of scale and specialization involved, this not only brings advantages to the users but also to the business providing the infrastructure. This service is also known as utility computing since the customers can pay for exactly the amount of service they use, like for electricity or water. It provides grids, clusters and virtualized servers, networks, storage and systems software designed to expand or substitute the functions of an entire data center. IaaS allows an internet business to develop and grow on demand.The best example of IaaS is Amazon’s Elastic Compute Cloud [EC2] and Simple Storage Service, however, IBM and other traditional IT vendors are also offering services, as is telecom-and-more provider Verizon Business.

Platform-as-a-Service (PaaS) is a set of software and development tools that are hosted on the provider’s servers. Developers can create applications using the provider’s API’s. It should be taken in account by the developers that there are not any interoperability standards maintained as yet, so some providers may not let them to take their application and put it on another platform. PaaS basically provides virtualized servers on which users can run existing applications or develop new ones without being worried about maintaining the operating systems, server hardware, load balancing or computing capacity. PaaS also allows a lot of scalability by design. Google Apps is one of the most famous Platform-as-a-Service providers. Other good examples include Microsoft’s Azure and Salesforce’s Force.com.

The third type which is Software-as-a-Service (SaaS) makes the broadest market. It is the most widely known and broadly used form of cloud computing.In this service, the providers allow the customers only to use their applications. The software through user interface interacts with the user. SaaS offers all the functions of a sophisticated traditional application. However, these applications are provided through a Web browser, and not by a locally-installed application. It reduces worries to a great extent about application servers, storage, application development and other common concerns of IT. Salesforce.com, Google’s Gmail and Apps, instant messaging from AOL, Yahoo and Google, Twitter and VoIP from Vonage and Skype are some common examples of SaaS providers.

In conclusion cloud computing is essentially a type of computing service model that can be used at anytime, that increases on demand and decreases when you don’t have a demand, making it something that appears quite attractive especially in the current economic climate.