Nanites eating through linear memory crystals
Linear memory crystals were a part of computer cores of Federation computers in the 24th century.
Linear memory crystals were found in the computer core of the Galaxy-class USS Enterprise-D. In 2366, evolved nanites used the crystals as nourishment. (TNG: "Evolution")
The Star Trek Encyclopedia, 4th ed., vol. 1, p. 481 defined "linear memory crystal" as the "optically refractive material used in isolinear optical chips, a key part of optical data processing devices."