It was supposed to be storage and processing but the directors thought that viewers wouldn't understand that a human brain could store (what was thought to be a

It was supposed to be storage and processing but the directors thought that viewers wouldn't understand that a human brain could store (what was thought to be at the time) a few terabytes of data, so they dumbed the concept down. It would have made so much more sense that Neo had the ability to manipulate the Matrix because his brain had admin access to it rather than "he's just some super who won the cybergenetic lottery".