I can see that. Before linux, there were lots of versions of unix from all kinds of vendors.

I'll bet all kinds of government contracts needed some way to compare vendors bidding on a contract

for example:

- These ran UTX-32, Gould's version of Unix based on a BSD 4.2 kernel developed by Gould's UNIX development centre in Urbana-Champaign (IL) to support multiprocessor systems

- AIX is based on UNIX System V with 4.3BSD-compatible extensions.

- DG/UX 1.00, released by Data General in March 1985, was based on UNIX System V Release 2 with additions from 4.1BSD.

- HP-UX (from "Hewlett Packard Unix") is a discontinued proprietary implementation of the Unix operating system developed by Hewlett Packard Enterprise

- Xenix is based on the operating system UNIX System V, which Microsoft licensed from AT&T Corporation in the late 1970s.