The MIT J-Machine multicomputer has been constructed to study the role of a set of primitive mechanisms in providing efficient support for parallel computing. Each J-Machine node consists of an integrated multicomputer component, the Message-Driven Processor (MDP), and 1 MByte of DRAM. The MDP provides mechanisms to support efficient communication, synchronization, and naming. A 512 node J-Machine is operational and is due to be expanded to 1024 nodes in March 1993. In this paper we discuss the design of the J-Machine and evaluate the effectiveness of the mechanisms incorporated into the MDP. We measure the performance of the communication and synchronization mechanisms directly and investigate the behavior of four complete applications.

An adaptive link assignment algorithm for the distributed optimization of dynamically changing network topologies is presented. The algorithm is responsible for determining the network connectivity by controlling the selection of links to be established and disconnected. This algorithm is designed to recover from predictable link outages as well as massive unpredictable failures. To minimize computational time complexity as well as to improve transient response. Some known graph-theoretic algorithms are utilized.>

A description is given of the Message-Driven Processor (MDP), an integrated multicomputer node. It incorporates a 36-bit integer processor, a memory management unit, a router for a 3D mesh network, a network interface, a 4K*36-bit word static RAM (SRAM), and an ECC dynamic RAM (DRAM) controller on a single 1.1 M-transistor VLSI chip. The MDP is not specialized for a single model of computation. Instead, it incorporates efficient primitive mechanisms for communication, synchronization, and naming. These mechanisms support most proposed parallel programming models. Each processing node of the MIT J-Machine consists of an MDP with 1 Mbit of DRAM.>