Multiprocessing: Functions and Features

An extended variant of the cache coherence protocol MESI is the less popular MOESI protocol. Next to the four conditions of the cache line modified, exclusive, shared and invalid MOESI adds owner status. If the cache line of a processor holds owner status, other CPUs can access the data of the owner CPU and do not have to access it in the main memory. This type of cache handling results in less memory accesses and in increased system performance. MOESI-based multiprocessor chipsets include AMD's 760MP.

The function of cache sharing is based on a simple principle: Processor 0 is owner of a cache line. In the event of a read access through processor 1 onto this area, this request is forwarded for example by the 760MP chipset to the fast cache of processor 0. An access to the slower main memory does not occur. This does not only decrease the response time for the read access, it also takes load off the memory bus which now is available for other accesses.