Abstract: This database system stores a plurality of storage units distributed to different types of memory media with different processing speeds. When storage units from the database accessible from a plurality of processing programs are read to a plurality of means for storing, the system places the applicable storage units under exclusive control to prevent them from being used by other processing programs and at the same time stores which memory medium is the source of the storage units read to the means for storing. When the storage units read to the means for storing have been updated, reference is made to the means for medium storing so that priority can be placed to the storage units whose source is the highest speed memory medium for writing to the database and for releasing of storage units from exclusive control upon completion of writing.