Index chamber
From Halopedia, the Halo wiki
The Index Chamber is a vast room within the core of every Library on each Halo. It is the storage place of the repository of all Forerunner knowledge and study of the Flood, the Index. The Index is a T-shaped object of similar size to a human forearm. It is both a store of information and the key to activating a vast, immensely powerful, Galaxy culling superweapon, the Halo system.
At the very center of the Index Chamber is the Index, suspended in mid-air more than likely by an anti-gravity device, as this can be seen when there's a glow around it, sort of like a shield. It can only be reached via a vast anti-gravity powered lift that remains docked four levels above the floating Index.[1]
This lift may require the authorization of the Installation's Monitor in order to be activated, starting the process of retrieving the Index and the final act of activating the Halos and wiping the Galaxy clean of sentient life.
