Codd's self-replicating computer

Abstract

Edgar Codd's 1968 design for a self-replicating cellular automaton has never been implemented. Partly this is due to its enormous size, but we have also identified four problems with the original specification that would prevent it from working. These problems potentially cast doubt on Codd's central assertion, that the eight-state space he presents supports the existence of machines that can act as universal constructors and computers. However, all these problems were found to be correctable, and we present a complete and functioning implementation after making minor changes to the design and transition table. The body of the final machine occupies an area that is 22,254 cells wide and 55,601 cells high, composed of over 45 million nonzero cells in its unsheathed form. The data tape is 208 million cells long, and self-replication is estimated to take at least 1.7 x 10(18) time steps.