Spartan neural interface

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 receipt 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 suits 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 soldier's 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 Spartan known for sure to have recieved this is John-117. He was given it due to him being Cortana's carrier, but the others may have also recieved it, although it was never explicitly stated. The only Spartan known to utilize the ability to carry an AI in their armor is the Master Chief and he has used this to great effect carrying Cortana who proved vital to him.