Anneke is 100% correct. Usually, there will be either a well in the cooktops that is kept just below boiling, or the responsible line cook will have a large pot of boiling water (refreshed as it boils down). As orders come in, a portion of par-cooked pasta is put in a receptable (that looks like a bain with lots of holes, with a handle) and dunked in the re-cooking bath. When it's done, it's pulled out, allowed to drain briefly, and then dumped into the saute pan with the sauce and other ingredients. Plated, finished with whatever, and ready to go.