To actualize an inexpensive mirroring system wherein the number of file systems which can be mirrored is not limited.
When a computer is actuated, an operating system and a driver program are read out of one of hard disks 21a and 21b. Consequently, an IDE driver 41 actualized as a driver of the physical layer once receiving a write indication having a place to be accessed specified with a logical address from a file system driver 34 sends the write indication to the logical address to both the hard disks 21a and 21b. Consequently, the hard disk 21a and 21b are mirrored together and the same data are written to the both. If the hard disk 21a or 21b has its abnormality detected, the IDE driver 41 rewrites a CMOS- RAM 13 so that when the computer is actuated, the normal hard disk is referred to.
YOSHIMI KOICHI
SAWAME YUICHIRO
UNITEC CO LTD