DUAL DEVICE FOR STORAGE MEDIUM

PURPOSE:To assure operation selection at the time of power-on again by setting bits showing the states of storage media of a master and a slave system. CONSTITUTION:When the communication control part 2C of a main control part 2 reads out the statuses of the recording media 0M and 1M of medium boards 0B and 1B through communication control parts 0C and 1C at the power-on time, the storage medium 0M of the medium board 0B of the master system (system 0) is selected; and PWON (bit indicating that the electric power is turned on for the storage medium) is cleared and USE (bit showing whether or not the storage medium is usable) and ACT (bit showing whether or not the storage medium is decided as an in-operation system) are turned on. Then the PWON clearing of the slave system (system 1) a matching process for master information by a mirroring process are performed. When the storage medium 0M of the system 0 is extracted thereafter, USE by the mirroring process is set for the medium port 1B of the system 1, so the system can begin to operate as the master system by a status read by system restarting.