Imagine a tiny nanomachine that has one function in life: to grab a molecule or an assembly of several molecules, and to move it a very short distance. Take many billions of these nanomachines and arrange them in a line. You now have a 'bucket brigade' that can be used to transport one type of molecule from one place to another. Now, take many of these lines and cluster them together, connect one end to a Source (essentially a factory that takes in air and water, and spits out neatly sorted atoms, molecules and molecule assemblies) and connect the other end to a matter compiler. This is a Feed.
The Feed has one or two other functions besides carrying raw building material. Computers can pull water ice off the feed to use for refrigeration, and return warm water. Each Feed line is centered around a vacuum tube which is used to evacuate matter compilers while they are in use, so nothing can disturb the fragile arrangement of molecules as it 'grows'. The Feed lines also serve as carriers of electrical power. Finally, the Feed is bidirectional - matter compilers can also decompile anything which came out of them in the first place, returning its component parts to storage facilities at the Source.
In The Diamond Age, the matter compiler is an integral part of most of society. Massive artificial islands built offshore with Sources at their centers are linked by gargantuan Feed lines to the mainland. These Feeds are usually topped by bridges, for the islands around the Sources are big enough for many to live on, and are usually inhabited by the New Atlantans (also known as the Neo-Victorians or Vickys). Feeds are built into every new building, but in places where there are pre-existing buildings - for instance, the older districts of London or Shanghai - Feed lines are carried on overhead poles or fixed to walls.
Feed usage is monitored for suspicious activity. For that reason, certain unscrupulous (or merely paranoid) individuals have their own private Sources.
Perhaps this should be an idea, not a thing...