JPH05242002

PURPOSE:To obtain the auxiliary storage device by which a host system can utilize an extension function which is not defined by a conventional command, as well by using this command, while reducing or avoiding debug of an operating system, etc., of the connected host system. CONSTITUTION:A conventional command having an instructing part and an instruction modifying part is used. A command recognizing means 14 recognizes an extension function command defined by data of the instruction modifying part, being different from data usually corresponding to data of the instruction part. When it is recognized to be the extension function command by the command recognizing means 14, a command executing means 16 executes its command. Accordingly, the auxiliary storage device which can utilize an extension function, as well can be obtained by using the conventional command.