during the duplexing is interrupted from information of the access information management table to the backup data or by copying the backup data to the original data application_number US 98293501 A description an embodiment in which the present invention is applied to the duplexed data memory system will be described below fig1 of the accompanying drawings is a block diagram showing a duplexed data memory system according to an embodiment of the present invention as shown in fig1 this duplexed data memory system comprises an original system composed of a main memory unit 1 a original channel unit 2 an original disk control unit 3 serving as an external memory control unit and an original disk unit 4 serving as an external memory unit and a subsystem composed of a main memory unit 5 a subchannel unit 6 a subdisk control unit 7 and a subdisk unit 8 similarly to this original system the original channel unit 2 and the original disk control unit 3 and the subchannel unit 6 and the subdisk control unit 7 are connected together by interface cables 9 and 10 also the original disk control unit 3 and the subdisk control unit 7 are connected by an interface cable 11 incidentally the main memory unit 1 and the original channel unit 2 are connected to a part of a host unit not shown or the host unit fig2 shows the internal arrangements of the original disk control unit 3 and the subdisk control unit 7 as shown in fig2 the.