IaaS
Infrastructure as a service
A Virtual Machine (VM) built by the enterprise is hosted by a cloud host. This provides control down to the operating system to the enterprise. The cloud host manages the physical hardware.
PaaS
Platform as a Service
The enterprise hosts web applications and services in the preconfigured virtual machines provided by cloud host. The cloud host manages all layers up to the operating system level. The enterprise manages the applications.
SaaS
Software as a Service
The enterprise consumes software services hosted by the cloud host. For example, a hosted Sharepoint server falls in this category.
