A derivative system of Unix.

　　BSD (Berkeley Software Distribution) is a derivative system of Unix, which was developed and published by the University of California at Berkeley from 1977 to 1995. Historically, BSD was once considered as a branch of UNIX-"BSD UNIX" because it shared the basic code and design with AT&T UNIX operating system. In the 1980s, many variants of UNIX licensing software were derived. More famous ones are Ultrix of DEC and SunOS of Sun Company. In 1990s, BSD was largely replaced by System V4.x and OSF/1 system. The later BSD version provided a platform for several open source software development and has been used ever since. "BSD" does not refer to any derivative version of BSD, but a branch of UNIX-like operating system.