The lowest level is infrastructure-as-a-service (IaaS). This is where pre-configured hardware is provided via a virtualised interface or hypervisor. There is no high level infrastructure software provided such as an operating system, this must be provided by the buyer embedded with their own virtual applications. Platform as a service (PaaS) goes a stage further and includes the operating environment included the operating system and application services. PaaS suits organisations that are committed to a given development environment for a given application but like the idea of someone else maintaining the deployment platform for them. Saas offers fully functional applications on-demand to provide specific services such as email management, CRM, ERP, web conferencing and an increasingly wide range of other applications.