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Thedrick

This is a very simple representation of a directory and it's use case. Obviously storing that much extra data has some overhead to it, and there are some solutions to work around that. Directories remove the requirement for processors to broadcast their reads and writes, but that can actually be detrimental if there are a lot of processors holding a given cache line because a processor will need to look up all other processors to send a message to, and then deliver them (hopefully in parallel), which could have a higher overhead than a broadcast.