Knights of The Old Republic
A Sith holocron was a device used by Sith to store information. Typically, they required use of the dark side to activate.
Sith holocrons were immediately identifiable with respect to Jedi holocrons, as they were usually pyramidal in shape, and etched with strange symbols and ancient hieroglyphs. Inscriptions usually lined the bottom of the device, and various dark incantations were found all over the smooth surface. At the holocron’s apex rested a black crystal, used to power the holocron’s store of information.
The design of the holocron was not the only way to discern its affiliation: Sith holocrons emitted a dark presence, creating tremors in the Force upon activation. It took a great deal of willpower for a Jedi to access the dark devices, and some of the more inexperienced Jedi often felt sickly or fell ill merely laying their gaze upon one.
Internally, however, Sith holocrons worked in much the same way as a Jedi holocron. The black crystal of the Sith holocron was made up of intricate lattices and vertices, capable of storing massive amounts of information, as well as the holocron’s Sith gatekeeper. The holocron was able to capture the appearance and cognitive networks of the holocron’s owner, and transform this into a three-dimensional hologram
The process by which holocrons were created was a very difficult one. In the days of the old Sith Empire, holocrons were prevalent among the Dark Lords just as Jedi holocrons were among Jedi Masters. Many rare materials had to be gathered, and much meditating on the will of the dark side was necessary to focus the Sith Lord’s power.
Sith holocrons originated from secrets shared with the Sith King Adas by Rakatan soldiers trying to gain the trust of the Sith ruler. Adas made a holocron based on Rakatan design and presumably the art of holocron making originated among the ancient Sith from this.