IaaS (infrastructure as a service) refers to the delivery of computing capacity and infrastructure as a service. Also known as HaaS (hardware as a service), IaaS encompasses all of the physical computing resources that support delivery of applications as a service. IaaS provides a major cost savings to organizations, as it provides access to additional computing capacity on demand, without the need for a major capital investment in additional hardware, etc. There are fewer players in the IaaS marketplace for this reason, as compared to PaaS (platform as a service) and SaaS (software as a service) providers, due to the large capital and operational expenses that are required to establish and maintain IaaS delivery.
IaaS can be delivered via a public cloud, a private cloud, a community cloud or a hybrid cloud. The infrastructure that is delivered by IaaS resides on the bottom layer of a cloud computing stack; with PaaS delivery occurring on the middle layer and SaaS delivery occurring on the top layer. In many cases, IaaS is bundled together with PaaS and SaaS delivery – as a complete cloud computing solution, as is the case with the hosted cloud services delivered by providers such as Amazon.com (i.e. its AWS offering), Google (i.e. its App Engine offering) and Microsoft (i.e. its Azure/AppFabric offerings). In addition, IaaS frequently incorporates virtualization into its design in order to facilitate optimal levels of utilization for physical computing resources. Network connectivity and storage capacity are also included in the IaaS definition, since these resources are a part of the physical computing resources that are delivered by IaaS.