Abstract : The performance of a PC cluster system is limited by the use of traditional communication protocols, such as TCP/IP, because these protocols are accompanied with significant software overheads. To overcome the problem, systems based on user-level message-passing interface without intervention of the kernel have been developed. VIA(Virtual Interface Architecture) is a widely adopted user-level message-passing interface which provides low latency and high bandwidth. In this paper, a software VIA system is implemented on an 8-node SCI(Scalable Coherent Interface) network based PC cluster. The system provides both message-passing and shared-memory programming environments and shows a maximum bandwidth of 84MB/s and a minimum latency of 8?? on application level. An average speed-up of 6.1 was obtained in executing the NAS parallel benchmark programs on the 8-node SCI-based PC cluster. The system also shows better performance in comparison with other comparable cluster systems in carrying out the parallel benchmark programs.