Differences between IaaS, PaaS and SaaS

Infrastructure as a Service (IaaS)Providing the fundamental building blocks of computing resources, IaaS takes the traditional physical computer hardware, such as servers, storage arrays, and networking, and lets you build virtual infrastructure that mimics these resources, but which can be created, reconfigured, resized, and removed within moments, as and when a task requires it. The most well known IaaS provider, Amazon Web Services, offers a variety of options, including their “EC2” computing platform, and “S3” storage platform.

Platform as a Service (PaaS)
Operating at the layer above raw computing hardware, whether physical or virtual, PaaS provides a method for programming languages to interact with services like databases, web servers, and file storage, without having to deal with lower level requirements like how much space a database needs, whether the data must be protected by making a copy between 3 servers, or distributing the workload across servers that can be spread throughout the world. Typically, applications must be written for a specific PaaS offering to take full advantage of the service, and most platforms only support a limited set of programming languages. Often, PaaS providers also have a Software as a Service offering (see below), and the platform has been initially built to support that specific software. Some examples of PaaS solutions are the “Google App Engine” system, “Heroku” which operates on top of the Amazon Web Services IaaS system, and “Force.com” built as part of the SalesForce.com Software as a Service offering.

Software as a Service (SaaS)
The top layer of cloud computing, Software as a Service is typically built on top of a Platform as a Service solution, whether that platform is publicly available or not, and provides software for end-users such as email, word processing, or a business CRM. Software as a Service is typically charged on a per-user and per-month basis, and companies have the flexibility to add or remove users at any time without addition costs beyond the monthly per-user fee. Some of the most well known SaaS solutions are “Google Apps”, Salesforce.com, and Microsoft’s “Business Productivity Online Suite”