Today, the cloud comes in three flavors which form the cloud stack: Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). SaaS is often built on a PaaS, which is built using IaaS.
IaaS is a platform offering raw computing power for service providers. It can also includes the servers, file or object storage, load balancers, network firewall, CDNs, etc. IaaS providers deliver these capabililites on-demand from a large cluster of equipment stationed in data centers. Amazon AWS, Microsoft Azure, Google Compute Engine, Rackspace, and IBM SmartCloud Enterprise are all leading providers of IaaS, Many big names in SaaS including Dropbox, Instagram, and Pinterest run on IaaS platforms provided by Amazon and others.
PaaS is a cloud environment or platform for developers to build cloud applications. Providers of PaaS deliver a database, an operating system, programming language execution capabilities as well as web servers. Like IaaS, the end user of the cloud application never interacts with the PaaS infrastructure. Microsoft Azure, Google Compute Engine, and Amazon AWS also have PaaS capabilities. Salesforce’s Force.com platform is another example of PaaS. The Salesforce apps available in the App Exchange are built on Salesforce Force.com platform.
SaaS is what most people think of when they hear the name of a familiar cloud service they interact with via a client such as a mobile app or browser. SaaS providers deliver software and applications via the cloud, which differ from other software in that it’s far more scalable. You are tapping into a system that is ready to use, as it is installed, maintained, upgraded and kept secure by the vendor. It’s also much easier for a software upstart to launch a new application in the cloud, which is why many SaaS apps from Slack to Salesforce dominate their respective product categories.