In 1979 I was developing the same application on several different systems with Basic. Durango (https://en.wikipedia.org/wiki/Durango_F-85 https://en.wikipedia

In 1979 I was developing the same application on several different systems with Basic. Durango (https://en.wikipedia.org/wiki/Durango_F-85 https://en.wikipedia.org/wiki/Durango_F-85) and Sord (https://en.wikipedia.org/wiki/Sord_Computer_Corporation https://en.wikipedia.org/wiki/Sord_Computer_Corporation) are 2 of the names I remember. Most had classic line numbers but one had a forward on full screen editor. You could fullscreen edit what was on the screen. This include adding new lines anywhere visible. Any action that made text scroll off the top was inaccessible and would be written to disk. To get back to earlier lines you had save all and restart.