BSD --
Berkeley Software Distribution, or
Berkeley Unix -- was a free operating system developed at the University of California, Berkeley during the 1980s, based on the original UNIX system by AT&T. Its legacy is most apparent in its direct descendants (collectively *BSDs) today, of which FreeBSD, OpenBSD and NetBSD are the most popular, but its influence and use spreads well beyond what most people are aware, and further than any other operating system that has ever existed. Indeed, all three of the world's most popular operating systems (Microsoft Windows, Mac OS X and GNU/Linux) rely on BSD code for some crucial part of their functionality.
Much of the TCP/IP stack in Microsoft Windows -- the software that allows you to access the Internet -- as well as networking tools such as
ftp.exe and nslookup.exe, have their source code derived from the historic Berkeley Unix. If you use Microsoft Windows, you rely on BSD to be able to browse this website, as well as to read your emails, chat with others over IM or VoIP, and install system updates across the Internet.
XNU, the kernel of Mac OS X -- that is, the very core of the system that makes it tick -- is heavily derived from BSD code, and unlike the BSD-derived software in Windows is open source. If you use Mac OS X, you rely on BSD in order for your computer to even run as it does. Because of this, Mac OS X is sometimes considered to belong to the *BSD family of operating systems.
In the early days of GNU, as well as later on when it achieved widespread use with Linux, there was much sharing of code between the GNU and BSD projects. For example, all *BSDs have historically used the GNU Compiler Collection (gcc) to build their source code. Much sharing of code has also taken place in the other direction, however, and today it would be difficult to imagine a GNU/Linux environment without BSD. Examples include OpenSSH, which is now the
de facto standard SSH implementation, and which is developed and maintained by the OpenBSD project, as well as a few wireless networking drivers (such as ath5k, used for some Atheros chipsets) that originated in BSDland and later found their way into Linux. If you use GNU/Linux, your OS itself may not rely on BSD to function, but it certainly does use it for some valuable functionality.
In addition to the above, the conceptual influence of BSD on modern operating system design has been dramatic. From
http://www.openbsd.org/lyrics.html#49:
"BSD 4.2 was not free, but it created and integrated so many new technologies that we all depend on today. Take a moment to consider how many things first available in BSD 4.2 you are using at this moment, to read this page -- sockets, AF_INET, virtual memory, etc.
Today, new releases of operating systems from well-known vendors contain less new features than BSD 4.2 did.
If only we could stop slacking and make a release like that!"So no matter which operating system you use, you are using BSD.