I think Jef Raskin credited Stallman and Emacs with inventing incremental search, saying that all text search was "either incremental or excremental". In The Humane Interface, a page or so earlier, he introduces it by saying:
> The less common strategy is the incremental search, a popular example of which is found in EMACS, an editor used with the UNIX operating system (Stallman 1993). In most implementations of incremental searches, as with the delimited search, the user first summons a dialog box that contains a field in which the user can enter the pattern. When he types the first character of the pattern, however, the system uses this character alone as a complete pattern and immediately begins to search for the first instance of that character in the chosen search direction. If an instance of that first character is found before the next character of the pattern is typed, the instance is selected ...
HandyFind, which has an ambiguous relationship with Raskin, says:
> Being able to find words as you type has been a popular feature in editors used by software programmers for a long time. The feature usually goes by the name "Incremental Search". The initial idea and implementation was done circa 1974 by researchers at MIT and later included in the popular word processor named "EMACS" (Richard Stallman, 1979). Recently, this feature has become more widespread and is sometimes referred to as Find As You Type, Search As You Type, Type Ahead, Inline Search, Interactive Search, Look-Ahead Search or Word-Wheeling. The claim that incremental search and LEAPing should be a fundamental part of making software easier to use was argued by Jef Raskin in his excellent book The Humane Interface, along with many other great ideas!
(http://www.handykeys.com/about.htm)
One critical difference is that Emacs incremental search is modal: sometimes (in incremental search minor mode) typing "x" adds it to your search string, and sometimes (in, say, fundamental-mode) typing "x" adds it to your document. The advance (as he saw it) of LEAP was that it's quasimodal, like Ctrl or Alt, and therefore much less prone to user error. It's also, I suspect, faster to use (though I've never had a Cat to try on); you'd think that going to the end of the sentence by typing LEAP-. would be about as fast as typing M-e, while using Emacs incremental search in the same way requires typing C-s . RET. That is:
press LEAP
press .
release LEAP || release .
vs.
press Ctrl
press S
release Ctrl || release S
press .
release . || press RET
release RET
which is just a significantly longer sequence of actions that must be carried out perfectly. (Actually you can release S and . in the sequence as late as you want, assuming you don't have key jamming problems, but you still need six steps instead of three.) I haven't modeled this with GOMS or anything but it seems like it would take longer.
As for "one big text file", yes, that was the major finding of Danny O'Brien's ethnographic work on "Life Hacks".