Memory files

Memory files could be accessed by the Fourth Doctor by searching through his own subconscious.

While facing off against the Ectoslime, the Doctor consulted his memory files - hoping that he had encountered the creature before and could therefore remember a weakness. While searching he listed off many other creatures he had encountered including; the "Abominable snowmen", Autons, Axos, Dæmons, Daleks and dinosaurs. Eventually he located his memory file on the Ectoslime and recalled that one of their distinguishing characteristics is a highly developed sense of humour. (COMIC: Doctor Who and the Iron Legion)