Mac OS X comes with Apache, an open source web server responsible for more than half of all the Internet's web sites.[*] At its most basic level, Apache runs as a daemon named httpd that supports the Hypertext Transfer Protocol (HTTP); it listens to web surfers' requests (on port 80, by default) and replies with response codes and web pages.
Apache's configuration information lies in the /etc/httpd directory, mainly in the file /etc/httpd/httpd.conf. This file sets up options through lists of directives and values, often mapped to filesystem directories and other criteria. Many of its options are highly specific to Mac OS X, so that Apache works "out of the box"; turning on web services with a single click in the Sharing pane (see the earlier section "Running Services Through the Sharing Pane") launches a full-featured web server on a fresh Mac OS X installation. Here are some highlights (and variances from the defaults that are in a platform-independent Apache installation):
DirectoryRoot directive defines the location of the server's default location for HTML files and other web-servable documents—in other words, what you'd see if you pointed your web browser to http://localhost/. Mac OS X sets this directive to /Library/WebServer/Documents/.
Following the usual Unix tradition, Mac OS X Apache lets a host's individual users build personal web sites in their own home folders, accessible by pointing a web browser to http://