Infrastructure as a Service, or IaaS, gives companies access to a vital web architecture, such as storage space, servers and connections, without the business need to buy and manage this Internet infrastructure.
Due to the economies of scale and specialization involved, this can benefit both the company that provides the infrastructure and the company that uses it. In particular, IaaS allows an Internet company a way to develop and grow on demand. Both PaaS and SaaS clouds are based on IaaS clouds, since the company that provides the software as a service also provides the infrastructure to run the software. The choice of using a IaaS cloud requires a good disposition to support complexity, but with that complexity comes flexibility. Amazon EC2 and Rackspace Cloud are examples of IaaS.
Platform as a Service (PaaS) platforms are created, often within IaaS Clouds by specialists to make the scalability and implementation of any application trivial and to make their expenses scalable and predictable. Some examples of a PaaS system include: Mosso, Google App Engine and Force.com. The main benefit of a service like this is that for so little money you can start your application without more stress than the basic development and perhaps a bit of adaptation if you are dealing with an existing application. In addition, PaaS allows great design scalability because it is based on cloud computing as defined earlier in the article. If you want a lean operations staff, a PaaS can be very useful if your application capitulates. The most important negative aspect of using a PaaS Cloud provider is that these services can implement some restrictions or concessions that will not work with your product under any circumstances.
Software as a service (SaaS) is relatively mature and the use of the phrase is prior to that of cloud computing. Cloud applications allow the cloud to take advantage of the software architecture, reducing the burden of maintenance, support and operations by having the application run on computers owned by the provider. GMail and Salesforce are among the examples of SaaS executed as clouds, but not all SaaS have to be based on cloud computing.
