The ``Berkeley'' Protocol

 

Cache line states:

• INVALID
• VALID : clean, potentially shared, unowned
• SHARED-DIRTY : modified, possibly shared, owned
• DIRTY : modified, only copy, owned

Read miss:

If another cache has the line in SHARED-DIRTY or DIRTY, it is supplied (changing state to SHARED-DIRTY). Otherwise the line comes from memory. The state of the line is set to VALID

Write hit:

No action if line is DIRTY. If VALID or SHARED-DIRTY, an invalidation is sent, and the local state set to DIRTY

Write miss:

Line comes from owner (as with read miss). All other copies set to INVALID, and line in requesting cache is set to DIRTY

• State Transition Diagram
• ...