Abstract: Test data are written into all password data areas SDAs located on each of surfaces of a disk arranged in a disk drive apparatus. SDAs each having a low error rate are selected. A predetermined number of SDAs dispersed on the plural disk surfaces are selected as effective SDAs from the selected SDAs. Position data of these effective SDAs are registered in an EEPROM. A password is written into each of the effective SDAs in a low error rate order and the disk drive apparatus is set to a locked state. A password input by a user is compared with the password written into each of the effective SDAs to release the locked state. Therefore, when an unlock command is input, the password is read from each of the effective SDAs in the writing sequential order of the password. When the password is correctly read, the read password is compared with the password input by the user. The locked state is released only when these passwords coincide with each other.

Abstract: When a write command is issued by a host computer data promptly transferred in response to the write command is stored in a write area of the data buffer. Thereafter, the start address of a read/write area is changed into the start address of the write area, data transferred from the host computer is stored in the data buffer to be sequential to the data stored in the write area. Thereafter, processing of sequentially the data stored in the read/write area in a magnetic disk is performed. When a read command is issued, the write area is set not to overlap the read/write area.