The dilithium crystal servo subsystem was a subsystem within the warp propulsion system of the Galaxy-class starships. The dilithium crystal was positioned in the center of the servomechanism inside the antimatter reactor core. An engineer from a control interface woould enter the parameters for the servo, which would move the device in the desired direction, in a simulation, then in a real world setting. By working in a simulation, the engineer tested their ideas and could experiment with the device, without putting the ship in danger. When inputting the parameters, in both situations, the dilithium chamber was off-line.
Design Team 7 of the Theoretical Propulsion Group was responsible for improving the design of this subsystem, which would be installed in the USS Enterprise-D in the early 2360s. (TNG: "Booby Trap", okudagram)