This article defines SaaS, PaaS, IaaS, and other such Cloud Computing terms.

While the markets seems saturated with sassy SAAS and PAAS definitions already, perhaps the myriad of slightly differently slanted definitions is making the concept a bit cloudy.

As I showed in a cloud computing diagram in an article last week about vendors, there are really three different kind of AAS forms: 1. Software as a Service (SAAS), 2. Platform as a Service (PAAS) and 3. Infrastructure as a Service (IAAS).

Traditional Web Application Deployment

In order to understand the ‘AAS’ aspect, we should look at the traditional web application deployment model first.

A. To deploy or use software, we must purchase servers from hardware vendors like Dell, HP, and IBM. Or, Sun, if you want to have storage. If we are intending this web application for external use, we must also buy data center equipment such firewalls, switches, routers, load balancers, VPNs etc, for performance quality and data security.Next, we must buy bandwidth and hosting services.

B. OK. Once we have the server, we’ll need to purchase and install an operating system, and subsequently an application server stack, such as Tomcat for Java, LAMP for PHP or Perl. Next, we’ll likely to need some database software like MySQL.

C. Once the hardware is bought, and the application server stack is built, now…, finally, we can install the actual web application.

Iaas, Paas and Saas Defined

By looking at this traditional software deployment model, we can identify the three steps easily:
A. Infrastructure
B. Platform
C. Software

So, IAAS, is offering all that’s mentioned at A. as a service, PAAS is offering all that’s mentioned at B as a service and finally SAAS is offering what is mentioned at C. as a service.