Difference between HTTP.SYS and WAS in IIS

HTTP.SYS (Hypertext Transfer Protocol Stack) is the kernel level components of IIS. All client request comes from client hit the HTTP.Sys of Kernel level. HTTP.SYS then makes a queue for each and every request for each and individual application pool based on the request.

Whenever we create any application pool IIS automatically registers the pool with HTTP.SYS to identify the particular during request processing.

WAS(Windows Activation Service) is a new feature of IIS, that allows all the features of the Windows Communication Framework stack, like non-HTTP channels and other stuff.

IIS is the web server that hosts the services that are activated via WAS.

WAS - is the new process activation mechanism that ships with IIS 7.0. WAS builds on the existing IIS 6.0 but is more powerful because it provides support for other protocols besides HTTP, such as TCP and Named Pipes.

For more details, go through IIS architecture