StarT-ng is a joint MIT-Motorola project to build a high-performance message passing machine from commercial systems. Each site of the machine consists of a PowerPC 620-based Motorola symmetric multiprocessor (SMP) running the AIX 4.1 operating system. Every processor is connected to a low-latency, high-bandwidth network that is directly accessible from user-level code. In addition to fast message passing capabilities, the machine has experimental support for cache-coherent shared memory across sites. When the machine requires memory to be kept globally coherent, one processor on each s i t e i s d e v oted to supporting shared memory. When globally coherent shared memory is not required, that processor can be used for normal computation tasks. StarT-ng will be delivered at about the time the base SMP is introduced into the marketplace. The ability to be both a collection of standard SMP and an aggressive message passing machine with coherent shared memory makes StarT-ng a good building block for incrementally expandable parallel machines.

In this paper we present two hardware components for high performance parallel computing: a superscalar RISC microprocessor with an integrated 400 megabytes/see user-level network interface (the 88110MP)J and a companion 8 x 8 low-latency packet router chip (ARCTIC).The design point combines very low message overhead and high delivered communications bandwidth with a commercially competitive sequential processor core. The network interface is directly programmed in user mode as an instruction set extension to the Motorola 88110. Importantly, naming and protection mechanisms are provided to support robust multi-user space and time sharing. Thus, jinegrain messaging and synchronization can be supported efficiently, without compromising per-processor performance or system integrity.Preliminary performance modeling results are presented.Permission10 copy without fee all or prui of ttiis material is granted, provided that the ccpies are not made or distributed for dueci commercial advantage, the ACM copyright notice and the title of the. publication a"d 624 its date appear, and no& k give" that copying is by &mission of the Association for Comfnuing Machinery. To copy dhenvise, or to repubhsb, requires a fee andbr specific pnission.