Since the early days of the Order and the first Jedi, holocrons had been used to store information they often contained vast amounts of important data. These devices were utilized by both Jedi, Sith. Often a holocron would have what was known as a "gatekeeper", a holographic representation of the one who created it who would assist an individual in accessing the knowledge inside after receiving the necessary password.
The Jedi Temple Archives were known to have many Jedi and even Sith holocrons safely contained within its libraries.
Cad Bane was sent by Darth Sidious to retrieve a valuable Jedi Holocron hidden within the Temple archives which detailed the names and whereabouts of every known force sensitive child in the Republic when combined with a memory crystal. The crystal was held by Jedi Master Bolla Ropal who was subsequently abducted and murdered by Bane in his quest to open the device, which could only be done with the Force. After Ropal succumbed to the torture, the Duros Bounty hunter inflicted on him in an attempt to get him to open the device. Bane used Anakin Skywalker and his Padawan Ahsoka Tano to fill his needs. Tano who had rushed into combat with Bane only to be easily overcome and captured was held hostage so that Skywalker would use the Force to open the crystal, which fearing for the life of his apprentice, he did.