(covers information from several alternate timelines)
A data core was an information storage device used by various civilizations.
The Earth deep space probe Friendship 1, launched in 2067, contained a data core that stored a large amount of scientific and cultural information. The core had been studied by the inhabitants of a Delta Quadrant planet, and was still intact as of 2378. (VOY: "Friendship One")
The primary data core of an automated repair station encountered by Enterprise NX-01 in 2152 incorporated living beings to boost its processing power. (ENT: "Dead Stop")
After USS Discovery was thrown into the mirror universe in 2257, Lieutenant Ash Tyler recovered a data core from the wreckage of a Klingon raider. The core was found to contain Vulcan data chips. (DIS: "Despite Yourself")
Later that year, a probe modified by an unknown party from the 28th century forcibly accessed and searched through the data core of shuttle DSC 05. (DIS: "Light and Shadows") A subsequent audit by Lieutenant Commander Airiam found multiple SQL injections by the probe, but no compromised files. (DIS: "If Memory Serves")
In 2377, the Hirogen prey hologram Kejal was attempting to reconfigure the data core of a photonic field generator to support her comrades' holomatrices, but could not determine how to increase the optronic capacity until she was assisted by Lieutenant B'Elanna Torres. (VOY: "Flesh and Blood")