PURPOSE: To gather status information without lowering the efficiency of the whole of the system, by reading status information of I/O devices independently of instructions of the host device by channels themselves when channels detect errors.

CONSTITUTION: When an error is detected on channel CH during data transfer from CPU to channel CH, channel CH stops the data transfer sequence and preserve status information of channel CH in log-out data buffer 3 and transmits the selective reset signal to the I/O device side and causes the ICC (interface control check) interrupt to CPU. I/O control device IOC which received the selective reset signal preserves its own status information in log-out buffer 5. The channel writes log-out data from IOC and its own log data into the memory of CPU after transfer of log- out data from IOC.