There is plenty of explanations of atomically precise manufacturing (APM) in text.
But I always found it hard to visualize because my intuitions for the nanoscale aren’t stellar and (maybe more importantly) I don’t know much about macroscale machines.
So, what are Drexler’s designs pointing to?
In conventional manufacturing, humans shape objects from the top down to make useful things.
A blacksmith shapes metal into a sword:
Today’s computer chips are made with photolithography – shining light on a plastic film to create desired patterns.
In both cases, the process is like making a sculpture of an elephant: start with a piece of rock (or metal, or plastic) and remove everything that doesn’t look like an elephant (or sword, or chip).
Drexler calls this bulk technology.
Productive nanosystems would assemble human-scale products from the bottom up, atom by atom, as in the video below.
I plan to go into the details of this video, but the high-level take-away is: molecular machines are assembled into a factory, which assembles large products.
That, at any rate, is the intended final destination.
As of 2019, the only examples of molecular machines come from biology on the level of proteins and protein complexes: