when sequential records are sequentially written to data blocks each having a fixed length on a disc storage medium , data to be saved are stored in a buffer of a main memory in addition to previously accumulated saved data , and a first data block a and a second data block c which is located apart from the first data block a at a distance of at least one block size , are updated alternately by moving all data , including the data to be saved and the previously accumulated saved data , stored in the buffer , to the data block . this method enables sequential records to be added and written while insuring the integrity of the data without lowering the data transfer efficiency .