operation supply source is supplied when the subsystem 140 is connected with the host 120 the host 120 reads the device information from the nand flash memory 144 of the subsystem 140 s 110 that is if the nand flash memory 144 receives a command and an address of a 90h according to predetermined timing the nand flash memory 144 outputs data e g maker code device code unique id code multi plane code stored in an input address the data is transmitted to the host 120 through the controller 142 the device information may include information on whether the nand flash memory 144 operates at 3 3v or 1 8v or whether it operates at either 3 3v or 1 8v the host 120 determines whether the subsystem 140 is a subsystem operating only at 3 3v depending on the read device information s 120 if the subsystem 140 operates only at 3 3v the host 120 controls the subsystem 140 to allow the nand flash memory 144 to perform the read and write operations in a well known manner s 130 if the subsystem 140 does not operate only at 3 3v the host 120 determines whether the nand flash memory 144 is operates at either 3 3v or 1 8v s 140 if the subsystem 140 operates at either 3 3v or 1 8v the host 120 controls the subsystem to allow the nand flash memory 144 to perform the read and write operations in the well known manner s 130 if the subsystem 140 does not operate at either 3 3v or 1 8v the host 120 performs predetermined error processing s 150 when the subsystem 140 operates at either 3.