Today, the industry recognizes three distinct cloud service models, each providing a different trade-off between control/flexibility and total cost.
- Infrastructure as a Service (IaaS): Virtual infrastructure hosting virtual machines and mostly existing applications e.g. Windows Azure, Amazon EC2
- Platform as a Service (PaaS): Cloud application infrastructure that provides on-demand application-hosting environment e.g. Windows Azure
- Software as a Service (SaaS): Cloud service model where an application is delivered over the Internet and customers pay on a per-use basis e.g. Office365 – SharePoint Online, Exchange Online, Skype for Business; Project Online, and CRM Online.