Since we’ve just passed the Matter Replicator trope, and since it may be relevant to an upcoming FAQ question, I thought I’d throw out some definitions relating to such things that may make things clear. Well, clearer.
A nanofac is the basis of nanofacturing technology. Think of it as essentially a 3D printer which can handle arbitrary molecular components with single-atom resolution. (It doesn’t have to: a lot of the time it can simply place pre-assembled multi-atom components picked out of its feed, but the point is that it can.) While it can use free-floating assembler nanites as part of its operation, the vast majority of the work is done in a supercooled vacuum chamber by an array of distant descendants of the atomic force microscope. The materials supply it needs is fed to it as a suspension of molecular components called nanoslurry available in a variety of forms, supplied as a utility from a central nanosource that makes the stuff from raw materials and recycles the return feed of all the stuff that the nanofacs don’t use.
Most important to note is that a nanofac is not a discrete thing you can buy itself – it’s just the term for the central construction array as a module.
What you can buy, on the other hand, is a cornucopia, which is a general-purpose construction device that comes in sizes ranging from desktop-printer-sized (the ubiquitous nanoforge) to dishwasher/fridge size. These are common household, etc., appliances, packaged as vending machines by companies like Valuematic Vending, and are basically a user interface/power supply/etc. wrapped around an appropriate nanofac. They can make pretty much anything you can describe in a recipe, or conceptual seed, to give it its formal name, although if it’s something too big to fit into its vacuum chamber what you’ll get is a heap of parts over several runs which you have to assemble manually following the v-tags after you get them out. (They may or may not bond permanently once you do this.)
A specialized cornucopia, on the other hand, is a fabber. These exist because in nanofacturing, there’s essentially a scale with versatility at one end and efficiency at the other. A cornucopia is a magical device that can make everything, but isn’t the fastest or most efficient way to make anything in particular.
So there are fabbers, which trade off that ability for greater speed and efficiency and customized user-friendliness in doing one particular thing. So while you want a cornucopia available to you, certainly, what you want in your wardrobe is a clothing fabber, in your kitchen is a food fabber, in your sickbay is a pharmafabber, in your wet bar is a cocktail fabber, etc., etc.
And finally, it’s worth noting that assembling things atom by atom, or molecule by molecule, is not actually a terribly efficient way to do things in the first place. It works fine for small objects, sure, where the convenience outweighs the inefficiency, and especially for those made out of lots of tiny components with fine detail to assemble. But large things, especially large things with large areas of relatively homogeneous structure, you really don’t want to make that way.
Which is where autofacs come in. An autofac is a automated assembly system that contains an array of nanofacs for making individual detailed components, but which also contains lathes and drills and presses and kilns and extruders and all manner of other macroscale manufacturing-process equipment, along with plenty of motile robots whose job is to do the assembly of all the different outputs of these processes into the end product. (So they take in nanoslurry for the ‘facs, but also metal ingots, ceramic powder, plastic granules, etc., etc., as their raw materials.)
These vary in size from the relatively modest autofacs you’ll find in most neighborhoods, belonging to companies like Ubiquifac, whose job is to construct large goods people have ordered on-line at a point relatively local to them for immediate delivery, up through larger factories – such as the ones that take nanoslurry and sheet metal in at one end and have finished vehicles drive out the other – all the way to truly giant many-square-miles really-can-build-anything complexes like the Hive.