Closely coupled multiprocessor systems

Abstract

This paper presents the results of an effort to determine the performance, operational characteristics, hardware and software requirements, and the potential applications base for a symmetric system of closely coupled multiprocessors. Based on experience described herein, multiprocessing provides an effective way to increase the range of system performance with a single CPU product line, thereby serving a wider class of applications and market areas and providing explicit growth channels for applications whose computing requirements grow in time.A prototype system has been built using PDP-11/40 processors, multiported memories, and UNIBUS windows, for the purpose of determining its performance and operational characteristics. The RSX-11M real time operating system has been modified to support multiprocessing on this configuration. Theoretical analysis has provided a mathematical expression for system throughput as a function of the number of processors, memory banks, and memory utilization factors. Performance measurements have been related to theoretical analysis so that analytic means can predict the performance of configurations beyond the scope of the prototype hardware.For certain applications, the system cost-performance ratio is improved. The cost effectiveness of multiprocessing is contingent upon low processor/bus utilization of memory, or a high degree of parallelism in the memory system, such as interleaving or banking. Furthermore, realization of the potential afforded by multiprocessing hardware can only be attained in properly structured multiprogrammed operating systems.