User blog comment:D. Cello/Assassinews 10/11 -- Desmond's Ancestry Revealed/@comment-91.182.19.112-20111013185115/@comment-3096856-20111013212756

Or in other words, the disks (Altaïr's Keys) have some recorded memories of Altaïr's life which acts like an Animus and lets Ezio view Altaïr's Memories. Its a lot like the DDS from Project Legacy.