A peripheral may include an identification information storage unit in which identification information of a download file can be stored; a program storage unit in which at least program data is stored and is overwritable; and a controller which controls overwriting of the program data. The download file may include at least the identification information or both the identification information and overwrite permission data. When said overwrite permission data is included, the controller may overwrite the program data with program data sent from the host device and return a response indicating a normal completion of data overwrite. When overwrite permission is not included in the download file, the controller may return a response of a normal completion of said data overwrite without overwriting said program data. The identification information of the download file may be stored in the identification information storage unit.