PURPOSE: To prevent the speed of access to a data file from decreasing by previously securing file areas large enough for the maximum number of records suitable to a user by a utility program and securing the continuation of file areas in the same data file.

CONSTITUTION: When a data file is registered, the name of the file to be registered is inputted on a keyboard and an initial effective record address point value is further inputted. Then the record length is inputted and the number of records is also inputted. Further, the product of the number of records and record length is divided by cluster side to find the quotient X and remainder Y. Then it is decided whether the remainder Y is 0 or not and 1 is added to the quotient X unless the remainder Y is 0. This quotient X is the number of clusters to be secured. The file area of the number of clusters which is the quotient X is cleared to zero and 'Registration completed' is displayed on a display device.