<P> In addition, the permissive nature of the BSD license has allowed many other operating systems, both free and proprietary, to incorporate BSD code . For example, Microsoft Windows has used BSD - derived code in its implementation of TCP / IP and bundles recompiled versions of BSD's command - line networking tools since Windows 2000 . Also Darwin, the system on which Apple's macOS is built, is a derivative of 4.4 BSD - Lite2 and FreeBSD . Various commercial Unix operating systems, such as Solaris, also contain varying amounts of BSD code . </P> <P> Starting with the 8th Edition, versions of Research Unix at Bell Labs had a close relationship to BSD . This began when 4.1 cBSD for the VAX was used as the basis for Research Unix 8th Edition . This continued in subsequent versions, such as the 9th Edition, which incorporated source code and improvements from 4.3 BSD . The result was that these later versions of Research Unix were closer to BSD than they were to System V. In a Usenet posting from 2000, Dennis Ritchie described this relationship between BSD and Research Unix: </P> <P> Research Unix 8th Edition started from (I think) BSD 4.1 c, but with enormous amounts scooped out and replaced by our own stuff . This continued with 9th and 10th . The ordinary user command - set was, I guess, a bit more BSD - flavored than SysVish, but it was pretty eclectic . </P> <P> Eric S. Raymond summarizes the longstanding relationship between System V and BSD, stating, "The divide was roughly between longhairs and shorthairs; programmers and technical people tended to line up with Berkeley and BSD, more business - oriented types with AT&T and System V ." </P>

History of the bsd family of operating systems