DIRECTORY STRUCTURE PERMITTING EFFICIENT WRITE-BACKS IN A SHARED MEMORY COMPUTER SYSTEM

A directory maintains status information over memory blocks in a shared memory computer system. The directory has a plurality of entries each corresponding to a respective block, and is organized into a main region and a write-back region. The main region has an owner field, identifying the current owner of the block. The write-back region has a writer field identifying the last owner to have written the block back to memory. To write a block back to memory, the owner enters its identifier in the writer field and writes the data back to memory without checking nor modifying the owner field. In response to a memory operation, if the contents of the owner field and the writer field match, memory concludes that it is the owner, otherwise memory concludes that the entity identified in the owner field is the owner.