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Incanam

This slide shows how directory based cache systems can be no worse than snooping based systems (in terms of communication cost). In the worst case (a write where all caches share data) we have a a broadcast akin to a snooping based system. However, more often than not, the communication will be a lot less, as in most programs, it will be rare for all caches to hold onto data. (Next slide shows actual data, and the slide after that shows reason why).