The prom (programmable read only memory) is an intregrated circuit within the controller holding all the operating parameters of the engine/transmission for the VIN of the car.
It is replaceable and can be removed from one controller to another. Or bought from the dealer if you supply the vehicle's VIN and state registration, sometimes.
Since yours is a 93, I would wager the IC is soldered into place. If you decide to buy a salvage yard controller, take your OEM ECM to a TV repair and the salvage yard ECM (OF THE SAME PART NUMBER) and have the two IC's changed. The repair people will have the correct equipment to do this.
Otherwise, bite the bullet......