Explaining BSD

Greg Lehey

<grog@FreeBSD.org>

In the open source world, the word “Linux” is almost synonymous with “Operating System”, but it is not the only open source UNIX® operating system. According to the Internet Operating System Counter, as of April 1999 31.3% of the world's network connected machines run Linux. 14.6% run BSD UNIX. Some of the world's largest web operations, such as Yahoo!, run BSD. The world's busiest FTP server of 1999 (now defunct), ftp.cdrom.com, used BSD to transfer 1.4 TB of data a day. Clearly this is not a niche market: BSD is a well-kept secret.

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 like this.

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Table of Contents
1 What is BSD?
2 What, a real UNIX®?
3 Why is BSD not better known?
4 Comparing BSD and Linux

1 What is BSD?

BSD stands for “Berkeley Software Distribution”. It is the name of distributions of source code from the University of California, Berkeley, which were originally extensions to AT&T's Research UNIX 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.

Unlike the Linux kernel, there are several different BSD kernels with differing capabilities.
The C library, the base API for the system.

The BSD C library is based on code from Berkeley, not the GNU project.
Utilities such as shells, file utilities, compilers and linkers.

Some of the utilities are derived from the GNU project, others are not.
The X Window system, which handles graphical display.

The X Window system used in most versions of BSD is maintained by one of two separate projects, either the XFree86™ project or the X.Org project. This is the same code as Linux uses. BSD does not normally specify a “graphical desktop” such as GNOME or KDE, though these are available.
Many other programs and utilities.

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