43BSD

43BSD is a shorthand term used in some historical Unix and BSD archives to denote the 4.3BSD release lineage produced by the University of California, Berkeley. It is not an official release name; canonical members of the 4.3BSD family include variants such as 4.3BSD-Tahoe and 4.3BSD-Net/2, among others. The label appears in informal documentation, mailing lists, and archival software collections as a compact way to refer to the 4.3BSD line that followed 4.2BSD.

The 4.3BSD family, released in the mid-1980s, introduced improvements over earlier BSD releases, including advancements in the virtual memory system, system performance, and portability. It also expanded networking capabilities, contributing to the maturation of TCP/IP and the BSD sockets API that would become standard in later Unix systems. Support for multiple hardware architectures common at the time, such as VAX and several workstation platforms, was a characteristic feature of these releases.

In practice, 43BSD is primarily of historical interest. It is discussed in historical accounts of BSD development and appears in preservation and emulation projects that seek to recreate early BSD environments. Modern BSD descendants—FreeBSD, NetBSD, and OpenBSD—trace their lineage back to the 4.3BSD era, though the exact usage of the term "43BSD" varies by source.

Availability of 4.3BSD derivatives is maintained in various archival repositories and vintage software collections, where enthusiasts and researchers study the evolution of BSD Unix and its networking stack.