The New Architecture in IIS 7 Modularity is the key word and was the ultimate design concept surrounding the complete redevelopment of the request processing pipeline in IIS 7. There are 40 different modules that make up the feature set of IIS, divided into eight categories. These modules are individually listed here, so you can see how different modules make up the functional stack that is IIS 7.
Common HTTP Web Server Components
Windows Process Activation Service
Health and Diagnostics
New: The Windows Process Activation Service
All installations of IIS 7 require a service new to Windows Server 2008, known as the Windows Process Activation Service, or WPAS. WPAS essentially maintains and administers all worker processes and application pools for IIS on any given machine, listening for new requests and either assigning them to existing processes or starting new work processes and marshalling the request to that process. WPAS also acts as a clearinghouse for configuration information for sites, application pools, and overarching web applications running on the machine.