Mini Tour: AT&T UNIX/i386 SVR4 v2.1 (x86)

This is the operating system AT&T UNIX SVR4 v2.1 running under VirtualBox. This was an official AT&T reference release of UNIX SVR4 for the PC. Ken Thompson and Dennis Ritchie were the 'inventors' of UNIX and worked at AT&T bell labs at the time. Whilst UNIX historically did exist as a specific operating system, UNIX is better thought of as a family of operating systems which can often be completely distinct from each other but share a common ancestry. UNIX is perhaps the most widely deployed 'family' of operating systems in history, serving as the basis for thousands of past and present operating systems as well as inspiring clones of UNIX such as GNU/Linux.

https://en.wikipedia.org/wiki/Unix