1.22. The X Window System
In 1988, an organization called the MIT (Massachusetts Institute of Technology) X Consortium was formed to promote and develop a vendor-neutral windowing system called the X Window System. (It was called "X" because it was a follow-on to a window system called "W" that was developed at Stanford University.) The organization eventually moved away from MIT and became known as the X Consortium. The XFree86 Project, Inc. is another major group developing X; they produce a freely redistributable version that's used on Linux and other Unix-like systems such as Darwin.
A window system is a way of dividing up the large screen of a workstation into multiple virtual terminals, or windows. Each window can interact with a separate application program -- or a single application can have many windows. While the "big win" is to have applications with point-and-click mouse-driven user interfaces, one of the most common applications is still a simple terminal emulator (xterm (Section 5.9)). X thus allows a workstation to display multiple simultaneous terminal sessions -- which makes many of the standard Unix multitasking features such as job control less important because programs can all be running in the foreground in separate windows. X also runs on many kinds of hardware, and it lets you run a program on a remote computer (across a network) while the program's windows are displayed on your local system. Because Unix systems also run on many kinds of hardware, this makes X a good match for Unix.
Unix boxes are, by default, characters-based systems. GUI systems are added to facilitate ease of use, as well as to provide access to a great number of sophisticated applications. The Mac OS X, though, is already a GUI, built on the BSD-based Unix environment, Darwin.
Though Darwin doesn't come with X Windows, you can download and install this, as well as X Windows-based GUIs, such as XDarwin (accessible at http://www.xdarwin.org) and OroborOSX (available at the Apple web site at http://www.apple.com).
--TOR and JP
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