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UNIX is a registered trademark of The Open Group in the United States and other countries.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this document, and the FreeBSD Project was aware of the trademark claim, the designations have been followed by the <quote>™</quote> or the <quote>®</quote> symbol.
$FreeBSD: head/en_US.ISO8859-1/articles/explaining-bsd/article.xml 51926 2018-06-29 07:33:14Z eadler $
In the open source world, the word <quote>Linux</quote> is almost synonymous with <quote>Operating System</quote>, but it is not the only open source <trademark class="registered">UNIX</trademark> operating system.
So what is the secret? Why is BSD not better known? This white paper addresses these and other questions.
Throughout this paper, differences between BSD and Linux will be noted <emphasis>like this</emphasis>.
What is BSD?
BSD stands for <quote>Berkeley Software Distribution</quote>. It is the name of distributions of source code from the University of California, Berkeley, which were originally extensions to AT&amp;T's Research <trademark class="registered">UNIX</trademark> operating system. Several open source operating system projects are based on a release of this source code known as 4.4BSD-Lite. In addition, they comprise a number of packages from other Open Source projects, including notably the GNU project. The overall operating system comprises:
The BSD kernel, which handles process scheduling, memory management, symmetric multi-processing (SMP), device drivers, etc.
The C library, the base API for the system.
<emphasis>The BSD C library is based on code from Berkeley, not the GNU project.</emphasis>
Utilities such as shells, file utilities, compilers and linkers.
<emphasis>Some of the utilities are derived from the GNU project, others are not.</emphasis>
The X Window system, which handles graphical display.
The X Window system used in most versions of BSD is maintained by the <link xlink:href="">X.Org project</link>. FreeBSD allows the user to choose from a variety of desktop environments, such as <application>Gnome</application>, <application>KDE</application>, or <application>Xfce</application>; and lightweight window managers like <application>Openbox</application>, <application>Fluxbox</application>, or <application>Awesome</application>.
Many other programs and utilities.
What, a real <trademark class="registered">UNIX</trademark>?
The BSD operating systems are not clones, but open source derivatives of AT&amp;T's Research <trademark class="registered">UNIX</trademark> operating system, which is also the ancestor of the modern <trademark class="registered">UNIX</trademark> System V. This may surprise you. How could that happen when AT&amp;T has never released its code as open source?
It is true that AT&amp;T <trademark class="registered">UNIX</trademark> is not open source, and in a copyright sense BSD is very definitely <emphasis>not</emphasis> <trademark class="registered">UNIX</trademark>, but on the other hand, AT&amp;T has imported sources from other projects, noticeably the Computer Sciences Research Group (CSRG) of the University of California in Berkeley, CA. Starting in 1976, the CSRG started releasing tapes of their software, calling them <emphasis>Berkeley Software Distribution</emphasis> or <emphasis>BSD</emphasis>.
Initial BSD releases consisted mainly of user programs, but that changed dramatically when the CSRG landed a contract with the Defense Advanced Research Projects Agency (DARPA) to upgrade the communications protocols on their network, ARPANET. The new protocols were known as the <emphasis>Internet Protocols</emphasis>, later <emphasis>TCP/IP</emphasis> after the most important protocols. The first widely distributed implementation was part of 4.2BSD, in 1982.
In the course of the 1980s, a number of new workstation companies sprang up. Many preferred to license <trademark class="registered">UNIX</trademark> rather than developing operating systems for themselves. In particular, Sun Microsystems licensed <trademark class="registered">UNIX</trademark> and implemented a version of 4.2BSD, which they called <trademark>SunOS</trademark>. When AT&amp;T themselves were allowed to sell <trademark class="registered">UNIX</trademark> commercially, they started with a somewhat bare-bones implementation called System III, to be quickly followed by System V. The System V code base did not include networking, so all implementations included additional software from the BSD, including the TCP/IP software, but also utilities such as the <emphasis>csh</emphasis> shell and the <emphasis>vi</emphasis> editor. Collectively, these enhancements were known as the <emphasis>Berkeley Extensions</emphasis>.
The BSD tapes contained AT&amp;T source code and thus required a <trademark class="registered">UNIX</trademark> source license. By 1990, the CSRG's funding was running out, and it faced closure. Some members of the group decided to release the BSD code, which was Open Source, without the AT&amp;T proprietary code. This finally happened with the <emphasis>Networking Tape 2</emphasis>, usually known as <emphasis>Net/2</emphasis>. Net/2 was not a complete operating system: about 20% of the kernel code was missing. One of the CSRG members, William F. Jolitz, wrote the remaining code and released it in early 1992 as <emphasis>386BSD</emphasis>. At the same time, another group of ex-CSRG members formed a commercial company called <link xlink:href="">Berkeley Software Design Inc.</link> and released a beta version of an operating system called <link xlink:href="">BSD/386</link>, which was based on the same sources. The name of the operating system was later changed to BSD/OS.
386BSD never became a stable operating system. Instead, two other projects split off from it in 1993: <link xlink:href="">NetBSD</link> and <link xlink:href="@@URL_RELPREFIX@@/index.html">FreeBSD</link>. The two projects originally diverged due to differences in patience waiting for improvements to 386BSD: the NetBSD people started early in the year, and the first version of FreeBSD was not ready until the end of the year. In the meantime, the code base had diverged sufficiently to make it difficult to merge. In addition, the projects had different aims, as we will see below. In 1996, <link xlink:href="">OpenBSD</link> split off from NetBSD, and in 2003, <link xlink:href="">DragonFlyBSD</link> split off from FreeBSD.
Why is BSD not better known?
For a number of reasons, BSD is relatively unknown:
The BSD developers are often more interested in polishing their code than marketing it.
Much of Linux's popularity is due to factors external to the Linux projects, such as the press, and to companies formed to provide Linux services. Until recently, the open source BSDs had no such proponents.
In 1992, AT&amp;T sued <link xlink:href="">BSDI</link>, the vendor of BSD/386, alleging that the product contained AT&amp;T-copyrighted code. The case was settled out of court in 1994, but the spectre of the litigation continues to haunt people. In March 2000 an article published on the web claimed that the court case had been <quote>recently settled</quote>.
One detail that the lawsuit did clarify is the naming: in the 1980s, BSD was known as <quote>BSD <trademark class="registered">UNIX</trademark></quote>. With the elimination of the last vestige of AT&amp;T code from BSD, it also lost the right to the name <trademark class="registered">UNIX</trademark>. Thus you will see references in book titles to <quote>the 4.3BSD <trademark class="registered">UNIX</trademark> operating system</quote> and <quote>the 4.4BSD operating system</quote>.
Comparing BSD and Linux
So what is really the difference between, say, Debian Linux and FreeBSD? For the average user, the difference is surprisingly small: Both are <trademark class="registered">UNIX</trademark> like operating systems. Both are developed by non-commercial projects (this does not apply to many other Linux distributions, of course). In the following section, we will look at BSD and compare it to Linux. The description applies most closely to FreeBSD, which accounts for an estimated 80% of the BSD installations, but the differences from NetBSD, OpenBSD and DragonFlyBSD are small.


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articles/explaining-bsd.pot, string 28