This thesis studies the file access performance in the distributed file systems and in the shared memory systems in comparative manners. The three major changes in computing practice such as the trend of the computer communication speed growth, the trend of the computing power growth and the trend of the transaction size growth have influence on the file access performance of the two computing paradigms. This study investigates the effect of the three on the file access performance comparatively in the two system paradigms using the validated virtual performance models. This study investigates the file access performance of various design alternatives such as multiple CPUs, multiple disks, multiple networks, multiple file servers, enhanced concurrency, caching, local processing, etc. and discusses various file system design issues comparatively in the two system paradigms in terms of the file access performance. Theoretical limit of the file access performance is investigated in many cases. The effect of the workload characteristics such as the workload pattern, the workload fluctuation, the transaction size, etc. on the file access performance is quantitatively evaluated in the two system paradigms. This study proposes the virtual server concept for the performance modelling based on queuing network theory and presents the virtual server models for the two system paradigms. The models which were used are found to predict the file access performance of the real systems very precisely. A parameterization methodology is proposed to obtain the performance parameters and their values. The workload characterization methodology is proposed which consists of the six steps of procedure and the six realistic and representative artificial workloads were obtained. The simulation is used as the main methodology and the analytic approach is used as an auxiliary method to solve the performance models in this research. The simulation results is compared with the analytic solutions case by case to be confirmed that the two are exactly the same as each other.