Perhaps my favorite video on YouTube is this glorious footage of someone hooking a 1930s teletype up to a computer running Linux:

https://m.youtube.com/watch?v=2XLZ4Z8LpEE

Watching it for the first time is what finally made ed click for me.

And yes, I was disappointed that the author clearly didn't understand why ed has the UI it does. It's about the teletype, not the computational cost of having a WYSIWIG UI.