MESI protocol

The MESI protocol is an Invalidate-based cache coherence protocol, and is one of the most common protocols which support write-back caches. It is also known as the Illinois protocol (due to its development at the University of Illinois at Urbana-Champaign). Write back caches can save a lot on bandwidth that is generally wasted on a write through cache. There is always a dirty state present in write back caches which indicates that the data in the cache is different from that in main memory. Illinois Protocol requires cache to cache transfer on a miss if the block resides in another cache. This protocol reduces the number of Main memory transactions with respect to the MSI protocol. This marks a significant improvement in the performance.Bus Request The MESI protocol is an Invalidate-based cache coherence protocol, and is one of the most common protocols which support write-back caches. It is also known as the Illinois protocol (due to its development at the University of Illinois at Urbana-Champaign). Write back caches can save a lot on bandwidth that is generally wasted on a write through cache. There is always a dirty state present in write back caches which indicates that the data in the cache is different from that in main memory. Illinois Protocol requires cache to cache transfer on a miss if the block resides in another cache. This protocol reduces the number of Main memory transactions with respect to the MSI protocol. This marks a significant improvement in the performance. The letters in the acronym MESI represent four exclusive states that a cache line can be marked with (encoded using two additional bits):