Back in 1979, Bernard Greenberg wrote a long document about Emacs on Multics. If you’re interested in the history of Emacs and how it evolved, you’ll probably enjoy reading through the document. It’s fairly long and detailed but all that detail is revealing.
It’s hard today to appreciate how difficult it was to implement Emacs—or any video editor—on a large mainframe like the H6000 system that Multics ran on. The problem was that the hardware didn’t really support per-character input and processing—let alone echoing the characters to the display—so special effort, including patching the OS, was necessary to make it work.
Multics was written in Multics PL/I, which despite being a complete, well designed language was not suited to incremental development. It was, therefore, a poor choice to implement Emacs with its extensibility. Instead, the controversial decision to use Lisp was made—remember that the original ITS Emacs was built as a set of macros on top of the TECO editor. That fateful decision with its profound effect on Emacs extensibility is still with us today. It’s success should give pause to those suggesting alternative languages such as Python, JavaScript, Ruby, or whatever as the Emacs’ implementation/extension language.
By reading Greenberg’s account, you see why Emacs is the way it is today. Although the text representation was different from today’s gap buffer, many of the original implementation details can still be seen in the current versions of GNU Emacs.
As I said, it’s a long document but worth reading if you’re interested in Emacs’ history and beginnings.
UPDATE : Goldberg –> Greenberg