I think it's more like a graph with edges between associated bits of information. It's easy to remember things in order, but random access is hard unless you've established links for it. For example, if you memorized how to play a song, each part links to the next but harder to ask someone what is the n-th note in a song, even if they can play the song. It would explain why making associations is a useful memory technique. Traversing this graph when you aren't near what you're looking for can be hard ("it's on the tip of my tongue").