Patent ID: 8068747

Claim:
An image forming apparatus comprising: a first non-movable mounting slot for mounting a first developing unit having first color toner if properly mounted; a second non-movable mounting slot for mounting a second developing unit having second color toner if properly mounted; a third non-movable mounting slot for mounting a third developing unit having third color toner if properly mounted; a fourth non-movable mounting slot for mounting a fourth developing unit having fourth color toner if properly mounted; and a control unit to sequentially select each of the mounting slots one at a time, to transmit a first signal to one of the developing units, mounted to a selected one of the mounting slots, to receive a second signal generated by the one of the developing units, mounted to the selected one of the mounting slots, and to determine whether the one of the developing units, mounted to the selected one of the mounting slots, is properly mounted based on the second signal generated by the one of the developing units, mounted to the selected one of the mounting slots.