Computer Systems: Architectures Modeling and Simulation : Third and Fourth International Workshops SAMOS 2004 Samos Greece July 21 23 2004 and July 19 21 2004. Proceedings This book constitutes the refereed proceedings of the 4th International Workshop on Systems Architectures Modeling and Simulation SAMOS 2004 held in Samos Greece on July 2004. Besides the SAMOS 2004 proceedings the book also presents 19 revised papers from the predecessor workshop SAMOS 2003. The 55 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on reconfigurable computing architectures and implementation and systems modeling and simulation