Reb Moshe Feinstein zt”l knew virtually all of Shas, Shulchan Aruch and many of their commentaries by heart.  He also possessed a flawless command of many works of the Rishonim and Achronim, the great authors of Torah works spanning the last thousand years.  He seemed to remember everything he ever learned.

R’ Moshe used to say that it is possible for a person to remember what he learns even without having a very good memory.  We have no trouble recalling incredible sights that we see only once in a very long time.  A person who was present once in his life at Cape Canaveral to watch the lift-off of the space shuttle will not forget that sight.  Similarly, if a person appreciates the beauty and pricelessness of every word of Torah, and savors every thought and teaching, he will recall what he learns.