Cloud computing is a general term for anything that involves delivering hosted services over the Internet. These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS).

A cloud service has three distinct characteristics that differentiate it from traditional hosting.

• It is sold on demand, typically by usage
• Users can access the service via the web.
• The Service is fully managed.

Significant innovations in visualization and distributed computing, as well as improved access to high-speed Internet, have accelerated the interest in cloud computing.

There are different levels where that model can be applied – and the desired benefits attained:

• Infrastructure-as-a-Service (IaaS) – Virtual machine services accessed over the network, providing compute and/or storage capabilities
• Platform-as-a-Service (PaaS)– Platform software services (such as web, application, database servers, enterprise service buses and other middle ware, with associated security mechanisms) on which web service-based applications can be built
• Software-as-a-Service (SaaS) – Applications provided as a service from the cloud, with end-user licences procured or “released” in line with changing demand.