Robert Comsol wrote:
The engine room presented in “The Ultimate Computer” is a double-edged sword. It could either be in the forward Main Sensor-Deflector Engine Room (where it takes over from the control computers already there) or the Warp Engine Room aft suggested by the power socket below the grated wall opening (sealed shut in Season Three because of the “M-5 experience”?).
Is "Warp Engine Room aft" the same as "in the saucer"? Because that's the only place the "The Ultimate Computer" engine room fit can be due to that long curving hallway they used so prominently in the episode. That would put at least one Season 2 style engine room in the primary hull.
There are definitely multiple engine rooms and it would appear that you can have as many or as few as you want depending if you count some as upgraded through the series or not.