Abstract: A control program for controlling an HDD and a rewrite program for rewriting the control program are stored together in a flash EEPROM. Upon entering the rewrite mode, a CPU in the HDD saves the control program in the flash EEPROM into the RAM. The CPU erases the flash EEPROM and restores the rewrite program of the RAM into the EEPROM. The CPU receives a new control program from a host computer and loads it in the flash EEPROM. The erasing of the flash EEPROM and the loading of the new control program are performed by the CPU in accordance with the rewrite program saved in the RAM.

Abstract: A data control system includes an external memory unit for storing data, a volatile memory for storing at-least-once accessed data from the external memory unit, a nonvolatile memory for storing frequently-accessed pieces of data among the data stored in the volatile memory, and a memory control unit for controlling the external memory unit and the nonvolatile memory. The frequently-accessed data is stored in the nonvolatile memory, so that when the system is powered down, the nonvolatile memory does not lose the frequently-accessed data. When the power is on, the frequently-accessed data can be again accessed rapidly.