PURPOSE: To inform the end of an output request quickly to a program by executing the write processing of output request and the read check after the write by separate processing.
CONSTITUTION: When the output request from the program to a disk is given, a firmware 6 checks the state of a sector corresponding to a sector state storage table 1, registers an output request sector ID and output information to an output request registration table 2 when a flag is '0', to send the output request to a disk device 8 and waits for the processing until the flag is '0' when the flat is at '1'. In receiving the end of write from the disk device 8, the firmware 6 informs the end to the program. On the other hand, a process to check the read after write is provided in the firmware 8 in addition to the process for the write processing. Thus, the timing informing the end of the write request to a sector to the program is quickened.