George Coulouris of Queen Mary College wrote an editor called em (editor for mortals, as opposed to ed, “the standard editor”), which was eventually mutated and evolved into an editor called ex or indeed vi, by Bill Joy.
Em is a QMC variant of the standard Unix text editor - ed. It includes all of ed, so the documentation for ed is fully applicable to em. Em also has a number of new commands and facilities designed to improve its interaction and increase its usefulness to users at fast vdu terminals (such as the ITT’s at QMC).
via this article in The Register:
where Bill Joy is quoted on the process of writing ex:
It took a long time. It was really hard to do because you’ve got to remember that I was trying to make it usable over a 300 baud modem. That’s also the reason you have all these funny commands. It just barely worked to use a screen editor over a modem. It was just barely fast enough. A 1200 baud modem was an upgrade. 1200 baud now is pretty slow.
9600 baud is faster than you can read. 1200 baud is way slower. So the editor was optimized so that you could edit and feel productive when it was painting slower than you could think. Now that computers are so much faster than you can think, nobody understands this anymore.
The people doing Emacs were sitting in labs at MIT with what were essentially fibre-channel links to the host, in contemporary terms. They were working on a PDP-10, which was a huge machine by comparison, with infinitely fast screens.
So they could have funny commands with the screen shimmering and all that, and meanwhile, I’m sitting at home in sort of World War II surplus housing at Berkeley with a modem and a terminal that can just barely get the cursor off the bottom line.