This made more sense in the days when 80 column by 25 lines were all that one could see into a computer, and BSD Unix shells had no sensible response to arrow keys ...<p>In those days, having three or four Emacs buffers where one could have a couple of files being edited, a shell session, and the output of the compiler was considered a blessing.<p>The rest of the "OS" moniker referred to things such as email and NNTP clients written in Elisp. It was really possible to start the day in Emacs and never leave, and I saw some people do it, although it was never quite my cup of tea. Fortunately, megapixel displays and window systems soon came to the rescue.