Various models are available depending on the services required. Software as a Service (SaaS) is the term used to describe applications installed and running on servers belonging to a third-party provider. In many cases, the applications are operated via a browser. In addition, all the data relating to the applications is stored at the provider’s computer centres. Platform as a Service (PaaS) makes a cloud-based development or production environment available to users for their own applications. Finally, Infrastructure as a Service (IaaS) provides users with virtual computer resources such as computing power, hard drive storage or server environments.