Multiprocessor system

A multiprocessor system having at least one processor and a cache memory per the at least one processor, the multiprocessor comprising a sharing memory type multiprocessor wherein a plurality of nodes having both the at least one processor and the cache memory, and a plurality of I/O devices share a memory through a network,

• the sharing memory type multiprocessor including a first means for recording one of both an identifier of the cache memory if the cache memory has an exclusive copy of a memory location capable of being cached and the report that no cache memory, otherwise, has the exclusive copy, wherein when one of the processor and the I/O device issues a read request for the memory location capable of being cached, the first means carries out one of:
• a first step of, if the identifier is recorded, transmitting a message for determining whether or not only the cache memory with the exclusive copy has an updated copy, and carrying out one of, when the cache memory with the exclusive copy has an updated copy, supplying data from the cache memory with the exclusive copy and of, otherwise, reading data from the memory;
• a second step of, if the report is recorded, reading data directly from the memory;
• and
• a third step of, if the identifier is recorded and a cache memory other than the cache memory with the exclusive copy has an updated copy, transmitting a message for determining whether or not all of the cache memories have updated copies, and carrying out one of, when at least one of all of the cache memories has an updated copy, supplying data from the at least one of all of the cache memories and of, otherwise, supplying data from the memory.