Common Cloud Models: There are many different service models available for the cloud, with more being defined all the time. The three most common models are Software as a Service, Platform as a Service, and Infrastructure as a Service. Each provides a different level of manageability and customization for your solution.
1. SaaS: SaaS, or software as a service, is a cloud service that revolves around, easily the largest and most well known cloud-based service, SaaS uses the cloud to deliver software to users, which is then usually accessed via your Web browser. Unlike physical software that you install on your computer, SaaS solutions are hosted on a provider's servers. SaaS helps deliver an application that can be widely distributed and accessed. An example of this would be Google's Gmail. This email-based application is fully managed and accessed over the internet.
2. PaaS: PaaS, or Platform as a Service providers offer you a higher level of management and control by providing access to a framework from the operating system, up. The underlying architecture of the host hardware network components and OS are typically managed by the vendor, who also take care of maintenance and support. This aspect makes it a great deployment service for developers who are free to concentrate on developing and not on maintenance.
3. IaaS: IaaS, or infrastructure as a service, is essentially cloud-based computers and resources. The most popular and well known type of IaaS is the virtual machine which is a digital version of a computer or server that is accessed over an Internet connection. The infrastructure is physically kept off site, and usually managed by a provider, but you access and interact with it as if it is located on your computer or in your office.