The new request-processing architecture and application 
isolation environment enables individual Web applications, 
which always run in user mode, to function within a self-
contained worker process. A worker process is user-mode 
code whose role is to process requests, such as returning a 
static page or invoking an Internet Server API (ISAPI) 
extension or filter. Worker processes use HTTP.sys to 
receive requests and send responses over HTTP.

IIs 6.0 architecture is based on Http.sys kernel and 
metabase configuration is in xml format security features 
all are same like iis5.0 but passport support included in 
6.0