Microsoft Azure IaaS:
This is the most basic Microsoft Azure offering, which at bottom
gives you a server in the cloud. Opting for that service, you are in
full control over the virtual machine, and are responsible for managing
everything from the operating system up to the application you are
running.
Microsoft Azure PaaS:
This service level also provides an operating system, a database, a
web server, an environment for executing your code, and additional
services such as identity management. By choosing PaaS for your project
needs, Microsoft Azure Cloud Service puts up with all of the tedious
operating system details for you, so you can focus all your energy on
what really matters to you – developing business applications your
customers will love.
Microsoft Azure SaaS:
Level where applications are built and hosted through third-party vendors that usually charge for a certain amount of service – Microsoft Office 365
is one such example. Today, most SaaS applications are built on a cloud
platform due to the low cost of entry and the ability to scale up as
your customer base grows.