JPS647369A - Data processing device - Google Patents

Abstract

PURPOSE:To change a medium without being conscious of the balance of the unwriting data on a main memory by writing into an external part memory device immediately after copying the data on the buffer for input and output in case of the external part memory device being capable of changing the medium. CONSTITUTION:When a writing request is received from an application program, an arithmetic control device 1 seeks the vacant buffer on a main memory device 3. In case of no vacant buffer existing, the data for buffer control is studied and the least used buffer is selected. The data for the buffer control of the selected buffer is then studied and when the contents thereof are not written on an external part memory device, an instruction is given to an external part memory control device 2 to write the unwritten data held by the buffer in the external part memory device. Then whether the writing external part memory device is changeable or not is studied and in the case of being changeable the unwriting data held in the buffer is written in the external part memory device. The external part memory device capable of changing a medium is thus made changeable at any time.