All three types of services; PaaS, IaaS, SaaS come under the cloud computing category. Depending upon the varying needs of customers, the services of cloud computing companies. While some clients may require only Platform as a Service, in which the client would like to hire the available platforms from which they can carry on their computing business, others may restrict their usage to Internet as a Service, through which the client can access the web services and web application and create a virtual desktop.
SaaS, on the other hand helps customers to outsource their software requirements, and use software which are also being used by the various other customers of the service provider, and meet their applications and business needs, on that software. Most of these services are pay per service and you pay a prescribed fee every time you avail a fixed unit of service usage, and you are not the owner of the software or platforms.
Though all the three methods offer services for which pay every time you use, care must be taken in availing the services. Most importantly, a customer must find out how secure their data is with the potential service provider. Even Internet as a service, can be manipulated as the web is accessed through the service provider, the host may have devices to rob personal data. More importantly the service provider may have located their hardware to distribute the service in a particular place, that can be sensitive to an organization's data.
In view of the risks involved, the emergence of some organizations such as the Cloud Security Alliance or CSA have brought the 3 types of services under one a single domain and allows certification to service providers who meet their guidelines.
As the three services offer three types of virtual worlds, whether it is the Platform to conduct or host your business in the PaaS method; or accessing web services and application through the Internet in the IaaS method, or making use of software through cloud computing and virtualization or your desktop, the services are classified under cloud computing, which in layman’s language refer to accessing various facilities owned by a third party, through the web.