Multiplexed computer system with the capability to copy data from one

Abstract

A multiplexed computer system allows memory accessing by a processor, a peripheral equipment or a like apparatus even during execution of memory copying to improve the processing performance during on-line maintenance. To this end, the multiplexed computer system includes a plurality of processing units which carry out the same operation in synchronism with each other. Each of the processing units includes a copy processor register for designating a processor to read out contents of a memory unit, copying circuits which transfer copies of the stored contents of the memory unit and data to be written into the memory unit in the same order as that of accesses to the memory unit to a memory unit of another processing unit, a copy mode flag indicating that memory copying processing for making the stored contents of the memory unit of the self system and stored contents of the memory unit of the other processing unit coincide with each other is proceeding, and a copy task flag indicating that the processor is reading out, during memory copying processing, the stored contents of the memory unit.