Cloud Service Models: Comparing SaaS, PaaS and IaaS

Defining what makes up Cloud Computing can be hard because it can be so many things. Many cloud computing vendors are not able to help clarify the definition because labeling products as Cloud Computing may make them appear current or more relevant. Even with all the marketing hype, Cloud Computing can be easily broken down into three different delivery models as are defined by NIST and known as an SPI model. SPI stands for Software, Platform and Infrastructure. With all the talk taken away, these models just represents hardware and software.

cloud computing

Cloud computing is what enables hardware and software to be delivered as services. The term service is typically used to indicate that they can be provided on demand and are typically paid on a per usage basis. The more you use the more you will pay. Cloud Computing provides computing services in the same way as a restaurant provides food, when we need computing space we use them from the cloud. The more we use these cloud services, the more we will have to pay. When we stop using the cloud services, then we stop paying.

Since computing can be a mean many things, Cloud Computing has a lot to deliver as a service. This is where the SPI models help organize things.

Software as a Service – SaaS

This is usually for end user applications that are sent on demand over the network on a pay per use basis. This software does not require client installation, only a browser and network connectivity are needed. One example of SaaS is Microsoft Office365. Before its launch, if an end user needed to use Word, they would then have to buy it, install it, then backup files, etc. With Office365, Word is available for a small monthly fee, it has no client installation and the files are automatically backed up, the software upgrades are performed automatically and the software is easily accessed from almost anywhere. If you decide you do not need Word anymore, then you stop paying the monthly fee. It is that simple.

Platform as a Service – PaaS

This type of service is typically used by software development companies to help run their software products. Software products have to have physical servers to run on, often Web servers too. This is all the platform that these application runs on. Building this service yourself can be a very time consuming task and it also needs to be constantly monitored and updated. PaaS provides all the platform out of the box enabling software applications to be given to the platform which will then execute them with no other requirements for administration of lower level components.

Infrastructure as a Service – IaaS

This type of service covers a huge range of features, from the individual servers to a private network, disk drives, numerous long term storage devices and email servers, domain name servers and messaging systems. All of these services can be produced on demand and they will often include software license fees for the operating systems and accompanying software that is installed on the servers. Some organizations will be able to build a complete computing infrastructure using IaaS on demand.

All of the services that are provided through cloud computing and can fit into one of the three delivery models above. Most end users will use SaaS, the software development teams will use PaaS and IT departments whose responsibility is the infrastructure will use IaaS. There is more to cloud computing and much more to learn, including topics like the automatic scaling and security abilities. But from a starting point, the categorizing of the deliver models should help customers and businesses understand that all parts of cloud computing are covered and that it can be useful for everybody involved.

To learn more about the cloud, cloud computing and what it means, visit Cloud Service on

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