Multiple-bus shared-memory system: Aquarius project

A multiple-bus architecture called a multi-multi is presented. The architecture is designed to handle several dimensions with a moderate number of processors per bus. It provides scaling to a large number of processors in a system. A key characteristic of the architecture is the large amount of bandwidth it provides. Each node in the architecture contains a microprocessor, memory, and a cache. The cache-coherence protocol for the multi-multi architecture combines features of snooping cache schemes, to provide consistency on individual buses, with features of directory schemes, to provide consistency between buses. The snooping cache component can take advantage of the low-latency communication possible on shared buses for efficiency, yet the complete protocol will support many more processors than a single bus can. The resulting protocol naturally extends cache coherence from a multi to a multi-multi. Cache and directory states are described. Concepts that allow efficient performance, namely, local sharing, root node, and bus addresses in the directory, are discussed.<>