“X, or the X Window System, is a graphical user interface for
most varieties of UNIX. XFree86 is a free version of X that is
used by both BSD and Linux. You can obtain more information
about what XFree86 is and how it is developed at XFree86.org.”
“Where do I get X?
XFree86 ships with FreeBSD, NetBSD, and OpenBSD. The install
program for each of the BSD’s has an option available for
installing the current version of XFree86. Additionally, XFree86 is
available in the ports collection. However, if you feel the need to
be more than current, you can download the latest and greatest from
www.xfree86.org and install it by hand at anytime. The stock
XFree86 distribution compiles out of the box on most any BSD
system.”
“How do I know if X is setup and where it installed to?
XFree86 usually installs to /usr/X11R6. On some systems it can
install to /usr/X11/. The configuration file for X is
/etc/XF86Config. The latest snapshot of XFree86 puts the config
file in /etc/X11/XF86Config.”