This Datacron unlocks the codex entry - Galactic History 74: Revan and Malak Fall
This datacron holds unheard of power and knowledge collected by an ancient race. You access its power and discover writings which are clearly only one small piece of a massive galactic history:
Finally, the Mandalorians had been routed. The Jedi generals Revan and Malak had killed Mandalore and hounded the remnants of the enemy fleet far beyond the boundaries of Republic space--and in so doing, performed terrible deeds and learned dark powers.
But there were darker days to come. During Revan's pursuit of the Mandalorians, he and Malak discovered the ancient Sith Empire hidden on Dromund Kaas. Realizing this Empire was the true threat to the Republic, Revan and Malak faced the Sith Emperor himself, intending to cut off the serpent's head--but the Emperor was too powerful. Overwhelmed by the Emperor's dark presence, they pledged themselves to his service.
The Sith Emperor anointed Revan and Malak as true Sith Lords and sent them to seek out the Star Forge, an ancient alien space station capable of producing powerful starships and droids. Never revealing the existence of the Emperor, Revan and Malak then returned to the armies that had followed them against the Mandalorians, armed their loyal servants with the Star Forge's weapons, and marched to war against the Republic.
This Datacron as well as Presence +4 are both located in The Nightmare Lands, so you will want to get both of these back to back. You will find this Datacron in The Boneyard heroic area to the west in The Nightmare Lands. Once in the Boneyard your first stop will be the northern destroyed walker which has a Fallen Trooper next to it whom you need to collect a Shield Decoder off of (Screenshots 1 & 2). Once you have the shield decoder you will want to head just northeast of where you found the body to the red force field area in the ground.
Here you will find a computer terminal that you must use to deactivate the force field, obviously this terminal requires the Shield Decoder you just found (Screenshots 3 & 4). Using the terminal deactivates the Red Force Field, which once deactivated you will want to ride the elevator down to the room below where you will find the Datacron.