jeremycole is correct, its closest real world analogy is a bubble memory or the short lived fad of using CCDs as a large linear memory (that went nowhere around the mid 80s) or most accurately its compared to an ancient mercury delay line (although Hg delay lines and CCDs are/were not persistent but their mechanical operation is similar)

There was a fad of endless loop tapes in the 80s... Exatron stringy-floppy. That is probably the closest physical analogy. Think "cassette tape interface" with electrically controllable R/W on an answering machine cassette, all conceptually of course this isn't how it actually worked. It had nothing to do with a floppy other than storing about the same amount of data, very java vs javascript like.

http://en.wikipedia.org/wiki/Exatron_Stringy_Floppy