Computing as a discipline in its own right (rather than as a discussion of whether it is Mathematics or Physics) is a reasonably young science. Wherever you trace its roots (e.g. Turing's paper in 1936, Babbage's engines, ATLAS, ENIAC or LEO) it's much younger than most modern nation states.
I've been programming (using the loosest definition) for close to 30 years but it still seems to me that I come across parts of its history that are new to me. While it shouldn't surprise me that while I studied computing at school, at University, post-grad and now as a day-job, that there is stuff I don't know, it still causes a small pause when I read an article about something which seems pivotal but about which I know absolutely nothing.
For instance, this news item describes a conference which looks to have sown the seeds for many things that have come since. It was 1968, the world was young, IBM was old, Microsoft and Sun barely in glint in their creators' eyes; the notion of separating hardware and software was new, the largest institutions had networks that numbered in the dozens of machines. Yet some of their conclusions are fresh and remain unresolved, in particular managing large projects. (The proceedings are fascinating and full of lessons for the future software engineer.)
The question is YASOP (*) - what piece of computing history do you think still has significance to our current industry but you feel people don't know enough about?
(*) Yet Another Stack Overflow Poll