| 摘要 |
A storage region formed of a nonvolatile storage device is divided into two blocks; block '0' and block '1'. In a process for writing data, the magic Nos. of the blocks '0' and '1' are checked. On condition that both the magic Nos. have a correct value, the sequential Nos. of the blocks '0' and '1' are compared so as to select the block whose sequential No. has a smaller value. The data to-be-written is written into the selected block. Subsequently, a value obtained by adding "1" to the sequential No. of the unselected block is written as the sequential No. of the selected block. Lastly, the magic No. is written into the selected block. On the other hand, in a process for reading data, the magic Nos. of the blocks '0' and '1' are checked. On condition that both the magic Nos. have the correct value, the block whose sequential No. has a larger value is selected, and the data to-be-read is read out of the selected block. According to the present invention, even in a case where the power of the storage device has turned off during the data write process and where the data write has not been completed, data before the write process remain. Even when the data are the set values or the likes of, for example, a computer system, the remaining data can be used for avoiding the state of the system incapable of starting.
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