ADDRESS CONVERSION METHOD

PURPOSE: To delicately protect storage by allowing a special bit and a conversion index buffering mechanism provided for each segment and a lock bit concerning each lien provided for a page frame to cooperate with each other. CONSTITUTION: A hierarchical storage system is constituted to convert a virtual address supplied by CPU to a real address by using the conversion index buffering mechanism and a page frame memory. In this constitution, plural segment registers are accessed by a segment identification field among the virtual addresses supplied by CPU. Then a segment identifier and the page offset field and the byte offset field of the virtual address are connected to generate a second virtual address having more bits than the virtual address to converts it to a real address. In addition, when the special bit is set to be a prescribed value, locking is executed for every line corresponding to a lock bit provided in each line.