An enhancement module was a piece of portable computer technology that could be used to provide large amounts of active memory for a tech cube. Together, these two pieces made an optronic data core.
In 2369, with the help of Reginald Barclay, the holographic James Moriarty and Countess Regina Barthalomew were stored in a tech cube equipped with an enhancement module to keep their holodeck program running continuously. The module had enough active memory to provide the characters a lifetime of experiences. (TNG: "Ship In A Bottle")
The box-like enhancement module was represented via a prop designed by Makeup & Effects Laboratories. Prop fabrication specialist Don Coleman found the idea of the device appealing. "The box was a vacuform pull with some pieces glued on the outside," explained Coleman. (Star Trek: The Next Generation 365, p. 289)