Source: https://starwars.fandom.com/wiki/Holocron/Legends
OVERVIEW
A holocron, short for holographic chronicle, was an organic crystal-lattice device which stored phenomenal quantities of data guarded by the device’s gatekeeper. Holocrons were used to hold information on Force techniques and instruction manuals by Force users beginning with the Sith and then the Jedi some three thousand years later.
DESCRIPTION
Most holocrons were shaped like polyhedra; Jedi holocrons were usually cubical, while Sith holocrons typically took the form of a pyramid, but other geometric shapes also existed. The Telos Holocron represents an atypical shape. Regularly, a holocron could be held in one’s hand.
The holocron employed patterns of organic crystals and hologrammic technology to capture the appearance and cognitive networks of the holocron’s owner, and transform this into a three-dimensional hologram. This gatekeeper acted as a guide through the holocron’s store of information, as a search and recovery engine with a more personal touch. These gatekeepers could relate stories from the holocron’s archives to events in the life of the one who activated the holocron. Jedi gatekeepers could sense the ability and level of a Jedi, and offer or restrict information accordingly—so that Padawans were not shown information too advanced and dangerous for their basic stage. Sith holocrons usually had the same restrictive mechanism like Jedi holocrons, but the gatekeeper could corrupt the unaware listener.
A great many holocrons were stored in the Jedi Archives on Coruscant, kept in a specific Holocron Chamber within the Jedi Temple. In addition to holding the holocrons created by Jedi in the field, the Archives also held the details on creating holocrons and directions on accessing them.
Usually, only Force-sensitive users could access a holocron, while data holocrons did not require Force sensitivity to access. This suggests that holocrons were partially powered by the Force. Once opened, Force-insensitive users could communicate with the gatekeeper as well as Force-sensitive users.
Some holocrons were activated by taking them apart with the Force and then inserting a special crystal that made the holocron readable. The Crystal was usually hidden away for safe-keeping by the founder of the holocron, but there have been instances in which a certain Jedi or Sith has protected the crystal at all times by keeping it on their person.