By Jeff Caruso, Network World (US) | Nov 17, 2011
The three primary types of cloud computing are IaaS, PaaS and SaaS - infrastructure, platform and software as a service, respectively. When you take a closer look, you'll see that what will decide this argument are your own company's needs and comfort level.
These services are made possible by virtualization, the ubiquity of high-speed networks and the capabilities of today's browsers. With these things in place, it becomes less necessary to own your own infrastructure, or even to own your own software. You can get what you need from the cloud, as you need it.
The easiest way to understand these as-a-service offerings is to start with SaaS, the most abstract layer and the one you may already be using today, even at a personal level. A simple example of SaaS is an online email service, like Gmail. If you use Gmail, you are not hosting your own email server. Google is hosting it, and you are simply accessing it through your browser-as-client. But email is just one application that your company uses, and today there are applications online for many business purposes.
SaaS is really geared toward the end users in your organization and doesn't take much to get started. The provider figures out how many resources to devote to your use of the application. The provider figures out the servers, the virtual machines, the network equipment, everything. You just point your browser at it.
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.