Turing Machines with Memory
A Turing machine (TM) uses an infinite tape with cells on it. At every update, a head, represented by a triangle, reads the color of the cell it is over, writes a color onto the same cell, and then moves either left or right.[more]
A memory Turing machine looks back steps to see what color the current cell was back then. Everything else stays the same compared to regular TMs. Turing machines with memory allow for more complex behavior than a regular TM.
Simply click on a cell under "initial conditions" to edit it, and then observe the Turing machine's reaction.[less]
 S. Wolfram, A New Kind of Science, Champaign, IL: Wolfram Media, 2002 p. 78.