This thesis presents the development and validation of a simulation model for an on-line IMS/VS configuration. A conceptual queueing model is developed from an actual system configuration and the simulation model parallels this conceptualization. The validation of the simulation model is carried out in three phases utilizing operational data from IMS logs and system monitors. This model is then used to evaluate system performance under a variety of operating configurations and system loads. A configuration which results in improved IMS response is the objective of the simulation analysis. / Master of Science