| 摘要 |
PURPOSE: A structure on a system for maintaining the coherence of a cache line in a common memory multiplexer system is provided by permitting a shadow directory to contain state information on a local main memory cached in an outer common cache to process efficiently memory requirement in cache-based system. CONSTITUTION: A shadow directory (40) contains only state information on a local main memory cached in an outer common cache. Respective shadow directories (40) contain plural sets (41) and the respective sets (41) contain plural items (42). The respective items (42) are the memory addresses of the local main memory. The respective items (42) contain the state bits of an existing bit P and a change bit M and a tag bit. The existing bit P shows whether one line in the local main memory is stored in the outer common cache and the change bit M shows whether the line of the local main memory is changed by the outer cache or not.
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