Unix was the first accessible real computer system like we know it. I worked with AT&T and Bell Atlantic for a project, and they provided several 3B2 systems for the project and for us to work on them in ~1992. They were used internally for all sorts of business applications, and the interface was typically a green screen like a Televideo 9xx. The only other systems I found that accessible and easy to use were Sun-like CAD workstation knockoffs that ran BSD 4.3 Unix in ~1989. https://en.wikipedia.org/wiki/3B_series_computers#3B2