Xanadu vs. the web: Part I - Prologue

I started out to write a post called "Hypertext vs. the web" which would try to compare early predictions of what hypertext was supposed to be against the way we use the web.  The idea was that, while we do indeed have documents with links embedded in them leading every which way, that's not the dominant way we use the web.  Wikipedia being an obvious and successful counterexample.

But you can't talk about early predictions of hypertext without talking about Xanadu.

So what was (or is) Xanadu?  In cold honesty and to the best of my understanding, Xanadu is a failed vision, but there's little to be learned from simply calling something a failure.  There can, however, be much to be gained from trying to understand what the vision in question was, and why it failed.  The full story is a long one, spanning decades and branching off in myriad directions, but I would like to take a few posts to explore the subject in broad outlines.  My aim is to compare a vision of what the web (or rather, its analog) might have been against what it actually turned out to be, and also to try to understand why things turned out the way they did.

As a bit of a disclaimer, I haven't used Xanadu (but that's part of the point: arguably no one has), nor have I seen a demo of it in its full form, nor am I closely or even not-so-closely acquainted with anyone involved, nor have I even corresponded with anyone involved.  In short, all I know about Xanadu is what I read on the web.  Given that the topic here is "Xanadu vs. the web", and there can be a certain antagonism between proponents of Xanadu and proponents of the web, this view is not without its distortions, but it's what I've got so I'm going with it.