[@Cyrania] Holocrons aren't like books, and they aren't taken out of the vault unless under the supervision of a Master. Also, Tython ;)

Though yeah most information is held on Datapads like E-Books (With physical books existing but extremely rare).

Holocrons themselves hold a type of hologram that when unlocked appears and gives you the information it holds in a visual/audio combination. ORRRR the information can be accessed through a terminal/datapad.

[url=http://starwars.wikia.com/wiki/Holocron#Description]Lovely Jubbly Holocron Information[/url]