BSD Operating Systems

BSD/OS (originally called BSD/386 and sometimes known as BSDi) was a proprietary version of the BSD operating system developed by Berkeley Software Design, Inc. (BSDi). BSD/OS had a reputation for reliability in server roles; the renowned Unix programmer and author W. Richard Stevens used it for his own personal web server for this reason.


Historic BSD

BSD was originally derived from Unix, using the complete source code for Sixth Edition Unix for the PDP-11 from Bell Labs as a starting point for the First Berkeley Software Distribution, or 1BSD. A series of updated versions for the PDP-11 followed (the 2.xBSD releases). A 32-bit version for the VAX platform was released as 3BSD, and the 4.xBSD series added many new features, including TCP/IP networking.

For many years, the primary developer and project leader was Bill Joy, who was a graduate student at the time; funding for this project was provided by DARPA. DARPA was interested in obtaining a programming platform and programmer's interface which would provide a robust, general purpose, time-sharing computing platform which would not become obsolete every time computing hardware was or is replaced. Such an operating system would allow Department of Defense software, especially for intricate, long-term finance and logistics operations, to be quickly ported to new hardware as it became available.

As time went on, code was later ported both from and to Unix System III and still later Unix System V. Unix System V Revision 4 (SVR4), released circa 1992, contained much code which was ported from BSD version up to and including 4.3BSD.

Comparison of BSD Operating Systems

There are a number of Unix-like operating systems based on or descended from the Berkeley Software Distribution (BSD) series of Unix variants. The three most notable descendants in current use are FreeBSD, OpenBSD, and NetBSD, which are all derived from 386BSD and 4.4BSD-Lite, by various routes. Both NetBSD and FreeBSD started life in 1993, initially derived from 386BSD, but in 1994 migrating to a 4.4BSD-Lite code base. OpenBSD was forked in 1995 from NetBSD. Other notable derivatives include DragonFly BSD, which was forked from FreeBSD 4.8, and Apple Inc.'s iOS and Mac OS X, with its Darwin base including a large amount of code derived from FreeBSD.

Most of the current BSD operating systems are open source and available for download, free of charge, under the BSD License, the most notable exceptions being Mac OS X and iOS. They also generally use a monolithic kernel architecture, apart from Mac OS X and DragonFly BSD which feature hybrid kernels. The various open source BSD projects generally develop the kernel and userland programs and libraries together, the source code being managed using a single central source repository.

In the past, BSD was also used as a basis for several proprietary versions of UNIX, such as Sun's SunOS, Sequent's Dynix, NeXT's NeXTSTEP, DEC's Ultrix and OSF/1 AXP (now Tru64 UNIX). Of these, only the last is still currently supported in its original form. Parts of NeXT's software became the foundation for Mac OS X which, together with iOS, is among the most commercially successful BSD variants in the general market.



OpenBSD aims at security, correctness, and being as free as possible. Security policies include revealing security flaws publicly, known as full disclosure; thoroughly auditing code for bugs and security issues; various security features, including the W^X page protection technology and heavy use of randomization; a "secure by default" philosophy including disabling all non-essential services and having sane initial settings; and integrated cryptography, originally made easier due to relaxed Canadian export laws relative to the United States. Concerning software freedom, OpenBSD prefers the BSD or ISC license, with the GPL acceptable only for existing software which is impractical to replace, such as the GNU Compiler Collection. NDAs are never considered acceptable. In common with its parent, NetBSD, OpenBSD strives to run on a wide variety of hardware.

The OpenBSD project has spawned numerous child projects such as OpenSSH, OpenNTPD, OpenCVS, OpenBGPD, PF and CARP. Many of these are designed to replace restricted alternatives.



NetBSD aims to provide a freely redistributable operating system that professionals, hobbyists, and researchers can use in any manner they wish. The main focus is portability, through the use of clear distinctions between machine-dependent and machine-independent code. It runs on a wide variety of 32-bit and 64-bit processor architectures and hardware platforms, and is intended to interoperate well with other operating systems. NetBSD places emphasis on correct design, well-written code, stability, and efficiency. Where practical, close compliance with open API and protocol standards is also aimed for. In June, 2008, the NetBSD Foundation moved to a two clause BSD license, citing changes at UCB and industry applicability.