A data core was part of the computer system of Lodestar Station 479 on Hurala. While investigating a distress call, the Tenth Doctor was trapped in the data core room. He used a spoon to tap out an SOS, which was finally detected five days later when the Wayfarer landed on Hurala for refuelling. (PROSE: Prisoner of the Daleks)
The Eleventh Doctor extracted the data core from the grating section of a New Dalek Paradigm's Supreme to get all its information about the Silence. (TV: The Wedding of River Song)