MOESI is an abbreviation for Modified, Owned, Exclusive, Shared, Invalid. It is a protocol commonly used in computer architecture and cache coherence systems to manage the consistency of data across multiple processors or caches in a multiprocessor system.
The term "Modified" refers to a cache state where a particular cache line has been modified by a processor and not yet written back to the main memory. In this state, the cache line is considered dirty and contains the most recent data.
"Owned" signifies that a cache line contains a copy of data that is exclusive to a particular processor. This state allows the processor to have read and write access to the cache line while other processors can only have read access.
"Exclusive" indicates that a cache line is present in only one cache and is not modified or shared with any other processor. This state allows the processor to have sole access to the cache line without requiring any communication with other caches.
"Shared" means that a cache line is present in multiple caches and is available for read access to all processors but cannot be modified. This state allows for data sharing between processors and requires a cache coherence protocol to ensure data consistency.
Lastly, "Invalid" refers to a cache state where a cache line is not present in the cache or is considered stale/outdated. In this state, the cache line needs to be retrieved from the main memory or from other caches before it can be used.
Overall, MOESI is a protocol designed to maintain cache coherence and ensure data consistency in multiprocessor systems by managing the states of cache lines and controlling access rights among processors.
