Nectar is a "network backplane" for use in heterogeneous multicomputers. The initial system consists of a starshaped fiber-optic network with an aggregate bandwidth of 1.6 gigabits/second and a switching latency of 700 nanoseconds. The system can be scaled up by connecting hundreds of these networks together.The Nectar architecture provides a flexible way to handle heterogeneity and task-level parallelism. A wide variety of machines can be connected as Nectar nodes and the Nectar system software allows applications to communicate at a high level. Protocol processing is off-loaded to powerful communication processors so that nodes do not have to support a suite of network protocols.We have designed and built a prototype Nectar system that has been operational since November 1988. This paper presents the motivation and goals for Nectar and describes its hardware and software. The presentation emphasizes how the goals influenced the design decisions and led to the novel aspects of Nectar.

Nectar is a "network backplane" for use in heterogeneous multicomputers. The initial system consists of a star-shaped fiber-optic network with an aggregate bandwidth of 1.6 gigabits/second and a switching latency of 700 nanoseconds. The system can be scaled up by connecting hundreds of these networks together.The Nectar architecture provides a flexible way to handle heterogeneity and task-level parallelism. A wide variety of machines can be connected as Nectar nodes and the Nectar system software allows applications to communicate at a high level. Protocol processing is off-loaded to powerful communication processors so that nodes do not have to support a suite of network protocols.We have designed and built a prototype Nectar system that has been operational since November 1988. This paper presents the motivation and goals for Nectar and describes its hardware and software. The presentation emphasizes how the goals influenced the design decisions and led to the novel aspects of Nectar.

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Multicomputersbuiltaround a general network are now a viable alternative to multicomputersbased on a system-speci~c interconnect because of architectural improvements in two areas. First, the host-network interface overhead can be minimized by reducing copy operations and host interrupts. Second, the network can provide high bandwidth and low latency by using high-speed crossbar switches and efficient protocol implementations.While still enjoying thejexibility of general networks, the resulting network-based multicomputers achieve high performance for typical multicomputer applications that use system-specijic interconnects. We have developed a network-based mtdticomputer called Nectar that supports these claims.This paper argues that it is feasible to build highperformance network-based multicomputers that use general networks instead of system-specific interconnects. Such a multicomputer is able to use em"sting hosts, including workstations and special-purpose processors, as its processors. While enjoying a high degree of flexibility, the underlying network can have performance comparable to that of a dedicated interconnect. This is true both for large messages,where bandwidth is important, and for small messages, where software overhead is typically the limiting factor. As a result, the types of applications that run on existing mult.icomputers also run efficiently on network-based multicomputers. At the same time, network-based multicomputers are able to take advantage of rapid advances in network and processor technology.The Nectar project is one of the fist attempts to build a high-performance network-based multicomputer. Nectar is composed of a high-bandwidth crosspoint network and dedicated network coproeessors. A prototype system using 100 Mb/s (megabits per seeond) links has been operational since early 1989. The system has currently 26 hosts, including a connection to a CRAY Y-MP via a 26 kilometer singlemode fiber link. The Nectar prototype has been used as a vehicle to study architectural issues in network-based multicomputers and high-speed networks. This paper is based on insights and experiences gained from the Nectar prototype.To further pursue our ideas, we are collaborating with an industrial partner (Network Systems Corporation) to develop a gigabit Nectar system capable of sustaining gigabit per second end-to-end communication.This new system will support the 800 Mb/s HIPPI (High-Performance Parallel Interface) ANSI standard, and will also have a SONET/ATM 664

We have demonstrated in our laboratory the rudimentary sensor-driven excavation of pipes buried at shallow depths . Our system integrates sonar range sensing, a surface depth map, segmentation for pipe searching , simple digging strategies , distributed computing and off-line simulation. Our hardware is a manipulator mounted to a backhoe and a vacuum tool simulates the air jet tool intended for field excavation.134