A removable hard disk drive is detachable from a computer apparatus, and
includes a storage medium for storing data from the computer apparatus
and a communication interface with the computer apparatus. Upon reception
of eject instruction issued by the computer apparatus, the removable hard
disk drive writes contents cashed in a cache memory into a disk, and
shifts to an ejectable state. Upon the completion of the shift to the
ejectable state, the removable hard disk drive externally outputs an
eject signal. A microprocessor which controls an eject mechanism executes
removable hard disk cartridge eject operation in response to the eject
signal.