The Data matrix was the positronic essence of Data's being. It contained all his memories and personality. In 2379, Data attempted to transfer his matrix to his brother B-4. Initially, the attempt appeared to have failed, with Geordi La Forge believing that B-4's brain was just not sophisticated enough to be able to handle the matrix. After Data was destroyed aboard the Scimitar, his matrix soon began to surface in B-4. (TNG movie & novelization: Star Trek Nemesis)