Optimum write-back strategy for directory-based cache coherence protocols

A system for optimizing the performance of a multiprocessor system having write-back caches and a multistage interconnection network connected to a shared memory, by allowing concurrent line transfer and write-back operations, comprising:

• a modified word buffer configured to store any modified words within a modified cache line when said modified words are written back from a cache;
• a line buffer configured to store an old cache line transferred from said memory, said old cache line corresponding in address identity with said modified cache line;
• and
• a global directory associated with said modified word buffer and said line buffer, said global directory configured to store state and control information pertaining to cache lines, said global directory configured to request a write-back of said modified words from said cache and concurrently request said old cache line from said memory, and said global directory configured to cause said modified word buffer and said line buffer to write, in combination, said modified cache line to a requesting cache.