SOFTWARE AS A SERVICE

In some ways, SaaS is very similar to the old thin-client model of software provision, where clients, in this case usually web browsers, provide the point of access to software running on servers. SaaS is the most familiar form of cloud service for consumers. SaaS moves the task of managing software and its deployment to third-party services. 

PLATFORM AS A SERVICE

PaaS functions at a lower level than SaaS, typically providing a platform on which software can be developed and deployed. PaaS providers abstract much of the work of dealing with servers and give clients an environment in which the operating system and server software, as well as the underlying server hardware and network infrastructure are taken care of, leaving users free to focus on the business side of scalability, and the application development of their product or service.

INFRASTRUCTURE AS A SERVICE

Moving down the stack, we get to the fundamental building blocks for cloud services. IaaS is comprised of highly automated and scalable compute resources, complemented by cloud storage and network capability which can be self-provisioned, metered, and available on-demand.

IaaS providers offer these cloud servers and their associated resources via dashboard and/or API. IaaS clients have direct access to their servers and storage, just as they would with traditional servers but gain access to a much higher order of scalability. Users of IaaS can outsource and build a “virtual data center” in the cloud and have access to many of the same technologies and resource capabilities of a traditional data center without having to invest in capacity planning or the physical maintenance and management of it.