Abstract The Computer systems for on-line control purposes have become popular in Japan. High reliability, quick system response, high through put and expandability are the main needs in these systems. To satisfy these diversified needs, Hitachi Control Computer 80 system has been developed with the modular configuration phylosophy. The system architecture has been designed with emphasis on distributed load sharing functions using multiple processors. Especially we think it most important to offer a large-scaled computer system without the deterrioration of responsiveness. In the multi-computer system, the main functions are the message exchanges, the control of other computer tasks and the management of common resources, that is, files and input/output devices. These functions are implemented by the interruptions and switching mechanisms of input/output interfaces. In this paper, we present and discuss the details of technologies in which we utilize the reliable, shared memory as the centralized system information. The technologies of system reliability are also discussed.