Turing machines are simple models of computers, invented by Alan Turing. They consist of a movable head that switches between states while reading and writing symbols (colors) on a tape.
The plot shows evolutions of the 2-state, 3-color Turing machine 596440, which is the smallest universal Turing machine.
The machine evolves on a tape with an infinite background pattern. Each row of squares gives one step in the evolution of the tape. The squares correspond to bits on the tape: blue, green, and red squares represent the digits 0, 1, and 2. The position of the head is indicated by drawing one pixel in each row darker (or lighter) if the head is in state 1 (or state 2).