Wild speculation about a sentient machine's learning process here. Much like a computer, an Exo could be accumulating his most recent memories and experiences in some sort of cache. Every once in a while (daily? weekly? monthly?), the Exo would have to enter a dormant state in which the data stored in this cache would be compiled, then undergo some form of analysis and be compressed in a format that can be stored for long term use in a larger database. Once compressed in such a fashion, the data could even be used to modify the Exo's operating system as some sort of patch that would affect his behavior and personality from now on. For instance, an Exo who recently faced numerous Fallen in battle could enter a dormant state once he has safely returned to the Tower. His combat experience would be analyzed: he could rate the effectiveness of his combat tactics, develop strategies tailored to any discernible enemy attack patterns and edit or flag relevant footage of his battle for future reference. Such vital data would then be assembled as a patch that would be immediately applied to his main operating system, effectively enhancing his combat efficiency in future encounters with the Fallen. Of course, that "learning" process would be applied to all experiences, from combat to social interaction. This brings us back to the arrival of our Ghost, outside the Wall in Old Russia. By bringing our Exo back from the dead, it would effectively be reviving it's main operating system. This system would, of course, lack any form of database to use as a reference. All the data compiled and stored for efficient long term use would have been lost. A blank slate. The most sophisticated computer the galaxy has ever known, connected to an empty hard drive, if you will. Well almost empty. Somewhere, hidden deep and brought forth by the light of the Traveler, a shadow of our former selves. A glimpse at who we once were, our past existence. A path to thread once more, in our tireless war against the oncoming Drakness: Titan, Hunter or Warlock. Edit: Excuse my English, this isn't my first language!