The Direct Neural Interface, or DNI, is a computer program that allows the user to have complete control over their physiology, as well at to integrate with computer systems.
In Halo and Red vs. Blue, the Neural Interface can be used to store vital data, such as an A.I. Construct.
In Call of Duty: Black Ops III, the DNI serves as a tactical advantage for cyber soldiers, connecting them to their cybernetically augmented body, the world around them, and to their teammates, and can also allow them to communicate with each other on closed channels.
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"The Direct Neural Interface, or DNI, connect's your mind with your new body, the world around you, and your teammates. It tells you info on the environment as well as your enemies. This version is also equiped with a Digimon Analyser, which eliminates the complex and slow use of a laptop computer. You can use that within 500 feet of a digimon. However, anymore than 500 can be taxing on the mind because it'll be slower and more obscure for the DNI to process." - James "Mustang" McCracken on the Direct Neural Interface.