The HTTP server is either the PTC HTTP Server (powered by Apache) or a commercial HTTP server such as IIS. The PTC HTTP Server is bundled with Windchill. Other HTTP servers can be purchased separately. An HTTP server must be present on each Windchill server host. The web server provides HTML pages and Java classes, as well as gives access to a Windchill HTTP gateway (described later in this section) as an in-process Java servlet.