MESI (4-state) Invalidation Protocol

• Add exclusive state

  • distinguish exclusive (writable) and owned (written)
  • Main memory is up to date, so cache not necessarily owner
  • can be written locally

• States

  • invalid
  • exclusive or exclusive-clean (only this cache has copy, but not modified)
  • shared (two or more caches may have copies)
  • modified (dirty)

• I -> E on PrRd if no cache has copy

  => How can you tell?
  

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