John Von Neumann's Self-Reproducing machine is implemented as a special case of a Universal Constructor embedded in a two-dimensional cellular automaton space. The Universal constructor is cable of operating on a tape in the same way as a Turing machine does. In fact, von Neumman's cellular automata are a generalization of a Turing machine where the computer and the tape are embedded in the same space. Moreover the computer is able to operate everywhere in the same way as it operates on the tape. As a result a Universal Constructor is able read descriptions of structures stored in tapes and to construct the corresponding structures in the embedding space. If provided with its own description, the Universal constructor will be able to self-reproduce, and to duplicate its genetic information stored in the tape. Below we show the animimated sequence of the construction of a small loop, described in the tape visible at the right of the constructor.
The source of a software implementation of von Neumann's cellular automaton space, together with some tools for building and evolving automata is available at ftp://ftp.ira.uka.de/pub/cellular-automata/jvn The original ms-dos version (developed in collaboration with Renato Nobili) of the same program is also available at this address.
A complete description of this implementation of von Neumann's self-reproducing machine can be found at:
U. Pesavento, An Implementation of von Neumann's Self-Reproducing Machine, Artificial Life Journal, 2, 337--354 (1995).
A Windows version of the software demonstrating this process has been implemented by Tim Hutton.
More information on this implementation and on von Neumann's Universal Constructor in general can be found on wiki.