- “I am the Knowing. I observe and record. I observe and collate.”— The Knowing
The Knowing was located behind a series of corridors buried underneath Ariel's mining facilities, and filled with traps, such as wall-mounted, motion-activated lasers. Its function was to observe, record, and organize information over the course of history. Presumably, it had been collecting information for the 100,000 years since the disappearance of the Forerunners after activating the Halo Array.
During the Battle of Ariel, ODSTs Dutch and Romeo found The Knowing after their stolen Phantom crash-landed in a room containing the missing colonists, whom the Covenant had been sending through the tunnels to find traps.
Upon entering the Knowing's chamber, it acknowledged their primacy, and offered to answer any questions they had. When it was revealed that the Covenant would be able to use the Knowing's information to destroy the human race "down to [their] last DNA strand," the ODSTs decided to tell the Knowing to self-destruct itself before the Covenant could reach it. Its destruction gave cause for the Covenant to leave Ariel, seeing no reason to remain after their goal had been destroyed - they didn't even bother to glass the planet.