The Spartan Neural Interface is an upgrade of the standard Neural Interface that is used by the UNSC SPARTAN-II supersoldiers. The Spartan Neural Interface was implanted in the Spartans upon the reception of their MJOLNIR Mark V armor.
It is assumed that, like the Neural Interface from which it is derived, it may not be removed without advanced surgery or killing the host.
In addition to the standard functions of a Neural Interface, the Spartan Neural Interface is unique in that it is designed to allow an AI to directly interface with the Spartan's brain. Therefore, the AI is said to reside both inside the armor and inside the wearer's mind. Essentially, it is in both places at once. The interface allows the AI access to most of the suit's internal systems, though the Spartan has override control. The AI is capable of significantly improving the data transfer rate between the motor cortex of the Spartan and the MJOLNIR's processing unit, further improving the Spartan's already lightning-quick reaction time.
The AI Data Crystal Chip is inserted into a socket near the base of the Spartan's skull in the MJOLNIR armor.
The only Spartans confirmed to receive and utilize the interface is John-117, Victor-101, and Naomi-010. John-117 used it to integrate Cortana, and this has proven vital over the course of the Halo trilogy. Victor-101 used it to integrate Iona. Naomi-010 used it integrate Black Box to fight the Jiralhanae on a cruiser in Halo: Glasslands.