Coupling PC based commodity technology with distributed computing methodologies provides on important advance in the development of single user dedicated systems. Beowulf is a class of experimental parallel workstations developed to evaluate and characterize the design space of this new operating point in price performance. A key factor determining the realizable performance under real world workloads is the means devised for interprocessor communications. A study has been performed to characterize a family of interconnect topologies feasible with low cost mass market network technologies. Behavior sensitivities to packet size and traffic density are determined. Findings are presented which compare more complex segmented topologies to the earlier parallel "channel bonded" scheme. It is shown that in many circumstances the more complex topologies perform better, and in some circumstances software routing techniques compare favorably to more expensive hardware switch mechanisms.

The Beowulf parallel workstation combines 16 PC-compatible processing subsystems and disk drives using dual Ethernet networks to provide a single-user environment with 1 Gops peak performance, half a Gbyte of disk storage, and up to 8 times the disk I/O bandwidth of conventional workstations. The Beowulf architecture establishes a new operating point in price-performance for single-user environments requiring high disk capacity and bandwidth. The Beowulf research project is investigating the feasibility of exploiting mass market commodity computing elements in support of Earth and space science requirements for large data-set browsing and visualization, simulation of natural physical processes, and assimilation of remote sensing data. This paper reports the findings from a series of experiments for characterizing the Beowulf dual channel communication over-head. It is shown that dual networks can sustain 70% greater throughput than a single network alone but that bandwidth achieved is more highly sensitive to message size than to the number of messages at peak demand. While overhead is shown to be high for global synchronization, its overall impact on scalability of real world applications for computational fluid dynamics and N-body gravitational simulation is shown to be modest.