Directory Based Systems
• In snoopy caches, each coherence operation is sent to
all processors. This is an inherent limitation.
• Why not send coherence requests to only those
processors that need to be notified?
• This is done using a directory, which maintains a
presence vector for each data item (cache line) along
with its global state.
• When IN is not a bus(like MIN etc), broadcast in not
implicit & requires additional hadware & time delay to
configure. A point to point comm is favoured.
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