Windows Activation Service (WAS)
IIS is usually thought of as a Web server, hosting Web pages and applications served up to Web browsers over the HTTP protocol. With IIS 6.0, IIS introduced Application Pools – a powerful runtime container that defined the process boundary around Web sites and applications, their process identity, as well as several other recycling, activation and shutdown behaviors. Application Pools are a powerful tool for Web administrators for isolating applications and managing them for health.
IIS7 has generalized the immensely powerful HTTP process activation model that IIS 6.0 introduced with Application Pools, and has made it available for all protocols. This protocol independent service is called the "Windows Process Activation Service". The Windows Communication Foundation ships with protocol adapters that can leverage the capabilities of the "Windows Process Activation Service". This can dramatically improve the reliability and resource usage of WCF services. This whitepaper walks you through a very basic WCF service that uses the "Windows Process Activation Service".
The IIS 7 components available on these Editions serve as supporting infrastructure for Microsoft’s Windows Communication Foundation (WCF.) Collectively the IIS 7 components that provide this infrastructure are referred to as the Windows Process Activation Service (WAS.) Users who install WCF based applications will not need to explicitly install WAS, rather these components will be installed by WCF as needed.
In IIS 7.0, Windows Activation Service (WAS) manages application pool configuration and worker processes instead of WWW Service. This enables you to use the same configuration and process model for HTTP and non-HTTP sites.
Additionally, you can run WAS without WWW Service if you do not need HTTP functionality. For example, you can manage an Indigo Web service through a listener, such as NET.TCP, without running the WWW Service if you do not need to listen for HTTP requests in HTTP.sys.
Windows Process Activation Service Samples