Difference between SaaS, Paas and IaaS

Cloud computing is where software applications, data storage and processing capacity are accessed over the Internet. In this article we’ll going to examine the three ways to “cloud compute”.

The three building blocks of cloud computing are software-as-a-service or SaaS, platforms-as-a-service or PasS and infrastructure-as-a-service or IaaS. All of these allow users to run applications and store data online. However each offers a different level of user flexibility and control.

In basic terms, SaaS allows users to run existing online applications. PasS allows users to create
their own cloud applications using supplier specific tools and languages. IaaS allows users to run any applications they please on cloud hardware of their own choice.

In more detail


SaaS is the easiest way to cloud compute and is where off-the-shelf applications are accessed
over the internet. For example, GoogleMicrosoft and Zoho each offer an online word processor, spreadsheet and presentation package. There are also some great creative SAS tools including PixlrAviary, as well as dedicated business applications like NetSuite and Salesforce. The advantage of SaaS is that applications are:

  • free or charged on a subscription basis
  • accessible from any computer on the internet
  • excellent for collaborative working


Platform-as-a-service or PaaS provides an environment and a set of tools that allow users to create their own new online applications. For example, Google have a product called App Engine that enables anybody to develop, run and maintain their own web applications on Google’s infrastructure. Microsoft also has a PaaS offering called Azure that allows users to develop and run Windows and other applications in Microsoft’s cloud. Salesforce is also a big player on the PaaS landscape with an offering called Lightning Platform.

All mentioned platforms will have some sort of free subscription which can be used to test the platform for free.

PaaS allow users to

  • create new online applications very rapidly at low cost
  • run applications privately within just one business or make them available publicly

PaaS can also:

  • limit developers to the programming languages and other tools offered by the PaaS provider
  • cause vendor locking as applications built on one providers platform cannot be moved to another


Infrastructure-as-a-Service or IaaS allows a business to run whatever applications it requires on a suppliers cloud hardware. This means that existing applications can be migrated from a company data center in order to reduce IT costs.

Cloud Infrastructure and IaaS

The fundamental unit of cloud infrastructure is the server. Today, servers can also be physical or virtual. Physical servers are discrete individual computers. In contrast, so termed a “virtual server
instances” are software controlled slices of real physical servers but is shared among many users via a process called virtualization.

Depending on the types of servers involved IaaS comes in four categories. Firstly, there is the most secure and costly option of the private cloud which is where a specific number
of physical servers are dedicated to one customer.

Secondly, we have dedicated hosting where a customer rents physical servers on-demand with the cost or a number of servers always matching their requirements.

Thirdly, there is hybrid hosting where a mix of physical servers and virtual server instances are rented on-demand in an effort to reduce cost and further increase flexibility.

Finally, we have cloud hosting where a customer rents virtual server instances on-demand and often on an hourly basis.

IaaS Marketplace

Several companies are now operating in the IaaS marketplace. for example Amazon offers a number of cloud hosting products that enable a variety of virtual server instances to be purchased by the hour. These can be launched in minutes using an Amazon Machine Image (AMI)  configured either to customer specification or containing software from suppliers like Oracle, Linux Sun, IBM, Microsoft, or other suppliers.

Alternatice IaaS providers include Rackspace, and DigitalOcean who offer all hosting categories from private clouds to cloud hosting.