A new class of computing system is emerging as an important low cost replacement for mid-level multiprocessors. Clustered PCs exploit the cost advantage of mass market manufacturing while retaining the performance benefits of leading edge fabrication facilities. The Beowulf project  has demonstrated that sixteen node systems can be assembled for less than $50,000 that deliver performance levels, including operation rate, memory and disk capacity, and memory and disk bandwidth, within a factor of 2 of systems costing 20 times as much. The software environment is provided by the Linux system, a POSIX-compliant, freely available and widely used operating system. Interprocessor communication uses message-passing, accessed via a complete implementation of the standard MPI application programmer interface. Beowulf systems can make multi-gigaflops level performance available to a much broader community due to their low cost while providing a user interface familiar to computational scientists working with typical massively parallel processors. The Halo World project will use a Beowulf system to analyze N-body simulation data. This system consists of 59 Intel Pentium-Pro processors (200 MHz clock) for an aggregate system peak performance of 11.8 gigaflops, 7.5 gigabytes of main memory, and 182 gigabytes of internal secondary storage. Targeting the Beowulf class of systems will, however, not preclude use of commercial massively parallel processors since use of standard application programming interfaces and operating system services will permit easy porting of the tools to other MPI/Posix platforms. In fact, most of the results presented here were obtained on commercial systems like the Intel Paragon.