Machines computations and universality : 4th international conference MCU 2004 Saint Petersburg Russia September 21 24 2004 ; revised selected papers This book constitutes the thoroughly refereed postproceedings of the 4th International Conference on Machines Computations and Universality MCU 2004 held in Saint Petersburg Russia in September 2004. The 21 revised full papers presented together with 5 invited papers went through two rounds of reviewing selection and improvement. A broad variety of foundational aspects in theoretical computer science are addressed such as cellular automata molecular computing quantum computing formal languages automata theory Turing machines P systems etc