Fault tolerant duplex computer system and its control method

A fault tolerant control method of a duplex computer system which includes a data processing section in each system to repair and announce a trouble generated in a process of transferring data or executing an arithmetic operation therein, and in which systems perform duplex running in synchronization while monitoring mutual operation situations, comprising:

• a fault diagnosis step of announcing information of the trouble generated in the system and executing processing instructed to the system;
• and
• a fault monitoring step of classifying pieces of trouble information received from the systems to record them as reparable trouble information or irreparable trouble information, and instructing trouble repairing processing to the systems based on the information,
• wherein in the fault monitoring step, the reparable trouble information of a relevant system is updated when a reparable trouble is received from each system, the irreparable trouble information of a relevant system is updated to instruct a diagnosis of the system when an irreparable trouble is received, and the pieces of trouble information from the systems are compared with each other, and synchronous processing is instructed by setting the system of a smaller amount of trouble information as an active system and the system of a larger amount of trouble information as a standby system when an out-of-sync situation is received.