Nectar is a high-speed fiber-optic network developed as a network backplane to support distributed and heterogeneous computing. A distinguishing component of the Nectar network is a highly programmable network processor called the communication accelerator board (CAB). The Nectar CAB has a flexible architecture, where almost all interactions between the network and the host are programmable. This structure allows arbitrary protocols to be implemented, evaluated, and utilized. A description is presented of the design, implementation, and usage of the Nectar CAB, and performance implications of its hardware features are discussed.>

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.