SOME-Bus-NOW: a Network of Wrkstations with broadcast

Networks of Workstations have been mostly designed using switch-based architectures and programming based on message passing. This paper describes a network of workstations based on the Simultaneous Optical Multiprocessor Exchange Bus (SOME-Bits) which is a low-latency, high-bandwidth interconnection network that directly links arbitrary pairs of processor nodes without contention, and can efficiently interconnect several hundred nodes. Each node has a dedicated output channel and an array of receivers, with one receiver dedicated to every other node´s output channel. The SOME-Bus eliminates the need for global arbitration and provides bandwidth that scales directly with the number of nodes in the system. Under the Distributed Shared Memory (DSM) paradigm, the SOME-bus allows strong integration of the transmitter, receiver and cache controller hardware to produce a highly integrated system-wide cache coherence mechanism. This paper examines switch-based networks that maintain high performance under varying degrees of application locality, and compares them to the SOME-Bus, in terms of latency and processor utilization.