Cache Coherence on a Slotted Ring

1 Abstract-The Express Ring is a new architecture under investigation at the University of Southern California. Its main goal is to demonstrate that a slotted unidirectional ring with very fast point-to-point interconnections can be at least ten times faster than a shared bus, using the same technology, and may be the topology of choice for future shared-memory multiprocessors. In this paper we introduce the Express Ring architecture and present a snooping cache coherence protocol for this machine. This protocol shows how consistency of shared memory accesses can be efficiently maintained in a ring-connected multiprocessor. We analyze the proposed protocol and compare it to other more usual alternatives for point-to-point connected machines, such as the SCI cache coherence protocol and directory based protocols.