These are some pictures I took from a FDM 2000 at TNO in Eindhoven.
You can clearly see the drivetrain. By the amount of cables I would say that the machine 'knows' exactly what the flowrate is.
This is the inside with the heating chambers. The chamber itself has the same diameter as the filament. The surrounding material is used as an accumulator to keep the temperature constant at any flowrate. So the chamber isn't wide but it is quite long.
The exchangelable tip and the solenoid construction.