Mac OS X: What is BSD?
BSD is the Berkeley Standard Distribution. In the early 1980s, the University of California at Berkeley was a major center of focus of UNIX activity. They adapted AT&T's System III and provided more sophisticated process management and network functionality. They distributed their version of UNIX, called the Berkeley Standard Distribution, for what amounted to the cost of goods. This, in turn, was widely adapted by academia and turned into the source material for further innovations by companies such as Sun Microsystems. Darwin incorporates elements of the BSD 4.4 distribution, which provide file system support, network services, symmetric multiprocessing support, and multi-threading facilities.
BSD also provides support for the "shell" environment. Simply put, a shell is an interactive, command-line interface that allows the user to control the operating system and accomplish tasks. UNIX is often confused with its shell interface. However, the best way to view the shell is as one of many possible ways to manipulate the core services.
For three decades, the easiest way to do this was via command-line interfaces, such as the Bourne shell (sh), the C-shell (csh), the Korn shell (ksh), tcsh, bash, and many others. However, starting in the 1980s, manufacturers started to experiment with many different ways to provide similar control via graphical interfaces, such as SunView, Motif, XWindows, and others. None of these graphical approaches has reached the level of integration that Mac OS X provides.
The shell environment is completely optional for most users. It provides maximum control over the operating system. It will appeal mainly to advanced system administrators, computer science students and experienced UNIX users. The only way to get to the shell in Mac OS X is for the user to locate the Terminal application and open it.
For a brief overview of Mach, see technical document 43137:
Useful Mac OS X Terms: What is Mach?
For a brief overview of BSD, see technical document 43139:
Useful Mac OS X Terms: What is BSD?
For a brief overview of Darwin, see technical document 43140:
Useful Mac OS X Terms: What is Darwin?
For in-depth information on Mach, BSD and Darwin, see the Apple Developer Connection site: