IaaS vs. PaaS vs. SaaS

Saas, A simple example of SaaS is an online email service, like Gmail. SaaS is really geared toward the end users in your organization and doesn't take much to get started.

IaaS is at the other end of the cloud spectrum. In this scenario, you want to maintain control of your software environment, but you don't want to maintain any equipment. You don't want to have to buy servers and put them in a climate-controlled room or any of that. Instead, you go to an IaaS provider and request a virtual machine.

PaaS is somewhere in between IaaS and SaaS. It's not a finished product, like SaaS, and it's not a tabula rasa, like IaaS. PaaS gives your application developers hooks and tools to develop to that particular platform. For example, Microsoft's Windows Azure gives you tools to develop mobile apps, social apps, websites, games and more. You build these things, but you use the APIs and tools to hook them into the Azure environment and run them there.