A method for controlling a portable personal device having facilities for storing and playing digital contents by a computer and an operation method of the portable personal device thereby are provided. The operation method of the portable personal device by control from a computer through a serial or parallel cable has the steps of (a) receiving a format request command from the computer for formatting an internal memory installed in the portable personal device or an external memory in an external memory card; (b) sending from the portable personal device a signal indicating that the portable personal device is ready to format to the computer; (c) receiving an execution command from the computer for executing the format request command received in the step (a); and (d) formatting the corresponding memory and then sending the result to the computer.