This book constitutes the refereed proceedings of the 4th International Workshop, PMBS 2013 in Denver, CO, USA in November 2013. The 14 papers presented in this volume were carefully reviewed and selected from 37 submissions. The selected articles broadly cover topics on massively parallel and high-performance simulations, modeling and simulation, model development and analysis, performance optimization, power estimation and optimization, high performance computing, reliability, performance analysis, and network simulations.