uses common resources and a single instance of both the object code of an application as well as the underlying database to support multiple customers simultaneously ¨ Google apps, Office 365, ZOHO, github, SalesForce.com, Oracle, etc. Platform as a Service: provides developers with a platform for hosting of web applications as a service ¨ Google AppEngine, Microsoft's Azure, Heroku.com, etc. Infrastructure as a Service: Delivery of computer infrastructure as a service ¨ GoGrid, Flexiscale, Layered Technologies, AppNexeus, Joyent, and Mosso/Rackspace, Amazon etc. Architecture SaaS PaaS IaaS Hardware