| The distributions from Berkeley were the first UNIX-based systems to introduce many important features including the following: Demand-paged virtual-memory support Automatic configuration of the hardware and I/O system A fast and recoverable filesystem The socket-based interprocess-communication (IPC) primitives The reference implementation of TCP/IP
The Berkeley releases found their way into the UNIX systems of many vendors and were used internally by the development groups of many other vendors. The implementation of the TCP/IP networking protocol suite in 4.2BSD and 4.3BSD, and the availability of those systems, played a key role in making the TCP/IP networking protocol suite a world standard. Even the non-UNIX vendors such as Microsoft have adopted the Berkeley socket design in their Winsock IPC interface. The BSD releases have also been a strong influence on the POSIX (IEEE Std 1003.1) operating-system interface standard, and on related standards. Several features such as reliable signals, job control, multiple access groups per process, and the routines for directory operations have been adapted from BSD for POSIX. Early BSD releases contained licensed UNIX code, thus requiring recipients to have an AT&T source license to be able to obtain and use BSD. In 1988, Berkeley separated its distribution into AT&T licensed and freely redistributable code. The freely redistributable code was licensed separately and could be obtained, used, and redistributed by anyone. The final freely redistributable 4.4BSD-Lite2 release from Berkeley in 1994 contained nearly the entire kernel and all the important libraries and utilities. Two groups, NetBSD and FreeBSD, sprang up in 1993 to begin supporting and distributing systems built from the freely redistributable releases being done by Berkeley. The NetBSD group emphasized portability and the minimalist approach, porting the systems to nearly forty platforms and pushing to keep the system lean to aid embedded applications. The FreeBSD group emphasized maximal support for the PC architecture and pushed to ease installation for, and market their system to, as wide an audience as possible. In 1995, the OpenBSD group split from the NetBSD group to develop a distribution that emphasized security. Over the years there has been a healthy competition among the BSD distributions, with many ideas and much code flowing between them. | 
