Berkeley Software Distribution (BSD), also known as Berkeley Unix, is an operating system derived from Unix developed at the University of California, Berkeley from 1977 to 1995. Key events included the first BSD release in 1977, the addition of virtual memory and networking capabilities, and the release of 4.2BSD and 4.3BSD, which popularized the BSD TCP/IP stack. Variants such as FreeBSD, NetBSD, and OpenBSD continue development of the BSD operating system today.