IIS 6.0 introduces a new kernel mode driver,
called HTTP.SYS, which is integrated directly
into the Windows Transmission Control
Protocol/Internet Protocol (TCP/IP) stack. Its
purpose is to route website requests through
to web application pools. In IIS 5.0, this task
was performed by the Inetinfo.exe process.
Additionally, HTTP.SYS maintains a cache that
can be used to serve requests for content
without having to switch out of kernel mode.