Molecular rod-logic, roughly similar to the mechanical calculators and
computers of the sort designed by Babbage and widely used before the
invention of the transistor. Only these would be implemented with nanoscale
components.
You can find a lot interesting stuff about this off of Ralph Merkle's
reversible computing page:
http://nano.xerox.com/nanotech/reversible.html
If you want to get into real detail about some of the technologies under
discussion, you could try http://nano.xerox.com/nanotech/helicalIntro.html
or http://nano.xerox.com/nanotech/mechano.html. The latter has pictures of
some of the mechanisms envisioned.
-- Eric Watt Forste ++ arkuat@pobox.com ++ expectation foils perception -pcd