PURPOSE: To display on a system console whether an unwritten data is left on a main storage or not, that is, whether there is a hindrance or not even if a system is stopped, by providing an increment means, a decrement means and an output means.

CONSTITUTION: By starting a buffer data write request processing by a buffer data write request control part 2, whether a dead buffer exists or a main storage 4 or not is checked. When there is no dead buffer, a buffer release is awaited, and when a dead buffer is obtained, a data is written in a data part of the obtained buffer in accordance with a request from a control part 1 for controlling a control part 2. Subsequently, the number of unwritten blocks which are held in a variable X storage part 8 is brought to an increment by a requested data number portion, and an unwritten flag in the buffer is turned ON. Next, whether a display for permitting a stop is outputted to a system console or not is checked, and when it is displayed, it is erased, and when it is not displayed, the processing is ended as it is.