Abstract: A distributed shared memory multiprocessor system based on a unidirectional ring bus using a snooping scheme comprises a group of processor nodes and a ring bus. The processor nodes are arranged in the form of a ring and one of the processor nodes generates a request signal for a data block, the remaining processor nodes snoop their own internal parts, and one of the remaining processor nodes provides the data block. The ring bus is used for connecting the processor nodes in the form of the ring and providing a path through which the request signal is broadcast to each of the remaining processor nodes and the data block is unicast to the processor node which has generated the request signal for the data block.

Abstract: A shared memory multiprocessor comprises a system bus operating under a split transaction protocol, at least one memory module coupled to the system bus and plurality of processor modules respectively having a processor and a cache. The cache maintains state information for each data block stored therein, which includes two distinct invalidated cache block states of COPYBACK-INVALID and NON-COPYBACK-INVALID. COPYBACK-INVALID and NON-COPYBACK-INVALID states commonly denote that the data block has been invalidated by another processor module in the shared memory multiprocessor. However, unlike COPYBACK-INVALID state, NON-COPYBACK-INVALID state further denotes that the processor module which most recently invalidated the data block has not copied back its updated copy of the block to the memory module, and, accordingly, the memory module does not contain the updated copy of the data block.