What's the difference between IaaS, SaaS and PaaS?


Cloud computing gave birth to many acronyms, but none are more important than IaaS, PaaS and SaaS; the building blocks of modern computing.

For the uninitiated these are: infrastructure-as-a-service (IaaS), platform-as-a-service (PaaS) and software-as-a-service (SaaS). Here we break down all three for you, including how IaaS stacks up vs PaaS and examples of the companies that have come to dominate each category.


Infrastructure-as-a-service (IaaS) is the simplest of the three categories to define, as it is broadly the same regardless of which public cloud vendor you choose. Simply put, IaaS is where a third party provides highly automated and scalable IT infrastructure - storage, hosting, compute, networking - out of its own global data centres and only charges for what you use.

So rather than owning assets like software licences or on-premise servers, companies can flexibly rent resources according to their needs.

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This has fuelled a crowded IaaS market, worth a total of $31 billion in 2018, up from $23.6 billion in 2017 according to research firm Gartner's latest figures.

It is a market that has been dominated by AWS since day one, back in 2006. Synergy Research Group's figures for Q1 2019 have AWS as the clear market leader globally when it comes to public IaaS and PaaS service revenues at 38 percent market share, which is down 2 percent quarter-on-quarter, followed by Microsoft at 18 percent, Google at 9 percent and Alibaba at 6 percent, all up a point respectively.

Despite AWS’s dominance, Microsoft has quickly gained ground under the leadership of "cloud first" CEO Satya Nadella, building a huge global cloud network of its own. Microsoft's recent move to increase the prices of only on-premise Office 2019 packages by 10 percent creates a clear incentive for customers to adopt a cloud-first attitude too.


Platform-as-a-service (PaaS) is possibly the hardest of the three cloud models to neatly define. The idea is to provide all of the basics of IaaS, as well as the tools and capabilities needed to develop and deploy applications securely. That could be middleware, database management, analytics or an operating system.

A platform-as-a-service should provide a developer with everything they need to build and deploy an application without having to do any provisioning of the underlying infrastructure themselves.

PaaS vendors tend to be the biggest technology companies, who can offer a broad range of capabilities for their customers on a platform. Examples include Google App Engine, Oracle Cloud Platform, Pivotal's Cloud Foundry and the Salesforce-owned Heroku.

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The underlying infrastructure for different PaaS offerings varies, so Oracle and AWS would prefer you run on their own infrastructure, and others are more agnostic. For example the SAP Cloud Platform can be run on top of AWS, Azure or GCP cloud infrastructure. Red Hat's OpenShift is similarly cloud provider-agnostic.


Software-as-a-service (SaaS) is where a piece of software is hosted by a third party and can be accessed over the web, normally just by logging in, and is generally charged on a subscription basis per user or 'seat'. This differs from the old model of buying and installing software on a machine or server manually.

SaaS is much more relevant for very specific applications, like email or customer relationship management (CRM) software. Anyone who has used a Google app like Gmail or Google Docs, or cloud file storage like Dropbox, will have used a piece of SaaS.

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Major SaaS vendors include Microsoft since it moved Office to the web-based Office 365, as well as enterprise software pioneers like Salesforce with its SaaS CRM solution, and Workday's cloud-based HR software.

Copyright © 2019 IDG Communications, Inc.

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