FreeBSD is a free Unix-like operating system descended from AT&T Unix via BSD. Although for legal reasons FreeBSD cannot be called “Unix,” it is a direct descendant from BSD, which was historically also called “BSD Unix” or “Berkeley Unix.” Due to its permissive licensing terms, much of FreeBSD’s code base has become an integral part of other operating systems such as Juniper JUNOS and Apple’s OS X.With the exception of the proprietary OS X, FreeBSD is the most widely used BSD-derived operating system in terms of number of installed computers, and is the most widely used freely licensed, open-source BSD distribution, accounting for more than three-quarters of all installed systems running free, open-source BSD derivatives.
Characterised in 2005 as “the unknown giant among free operating systems”, FreeBSD is a complete operating system. The kernel, device drivers, and all of the userland utilities, such as the shell, are held in the same source code revision tracking tree. (This is in contrast to Linux distributions, for which the kernel, userland utilities, and applications are developed separately, and then packaged together in various ways by others.) Third-party application software may be installed using various software installation systems, the two most common being source installation and package installation, both of which use the FreeBSD Ports system.
FreeBSD development began in 1993 with a quickly growing, unofficial patchkit maintained by users of the 386BSD operating system. This patchkit forked from 386BSD and grew into an operating system taken from U.C. Berkeley’s 4.3BSD-Lite (Net/2) tape with many 386BSD components and code from the Free Software Foundation. After two public beta releases via FTP (1.0-GAMMA on 2 September 1993, and 1.0-EPSILON on 3 October 1993), the first official release was FreeBSD 1.0, available via FTP on 1 November 1993 and on CDROM on 30 December 1993. This official release was coordinated by Jordan Hubbard, Nate Williams, Rodney W. Grimes and named by David Greenman. Walnut Creek CDROM agreed to distribute FreeBSD on CD and gave the project a machine to work on along with a fast Internet connection, which Hubbard later said helped stir FreeBSD’s rapid growth. A “highly successful” FreeBSD 1.1 release followed in May 1994.
However, there were legal concerns about the BSD Net/2 release source code used in 386BSD. After a lawsuit between then Unix copyright owner Unix System Laboratories, and the University of California, Berkeley, the FreeBSD project re-engineered most of the system using the 4.4BSD-Lite release from Berkeley, which, owing to the lawsuit, had none of the AT&T source code earlier BSD versions contained, making it an unbootable operating system. Following much work, the unencumbered outcome was released as FreeBSD 2.0 in January 1995.
FreeBSD 2.0 featured a revamp of the original Carnegie Mellon University Mach virtual memory system, optimized for performance under high loads. This release introduced the FreeBSD Ports system, which made downloading, building and installing third party software very easy. By 1996, FreeBSD had become popular among commercial and ISP users, powering sites like Walnut Creek CD-ROM, Yahoo! and Hotmail. The last release along the 2-STABLE branch was 2.2.8 in November 1998.FreeBSD 3.0 brought many more changes, including the switch to the ELF binary format. Support for SMP systems and the 64-bit Alpha platform were added. The 3-STABLE branch ended with 3.5.1 in June 2000.
source from :http://en.wikipedia.org/wiki/FreeBSD