# MOESI

**[MOESI](https://en.wikipedia.org/wiki/MOESI_protocol)** (Modified/Owned/Exclusive/Shared/Invalid) extends MESI with an Owned state to avoid unnecessary write-backs to memory when a dirty line is shared. The Owned state lets dirty data circulate cache-to-cache while only one designated owner is responsible for eventual write-back to memory.

MOESI is used by AMD's Opteron and EPYC families, where cache-to-cache transfer savings matter significantly on multi-socket systems.

## Example

MOESI's Owned state avoids memory write-back on cache-to-cache transfers.

```
M --[snooped read from another core]--> O (owner), S (requester)
O --[direct cache-to-cache transfer]--> no memory write-back needed
```