We present simulations and performance results of nuclear burning fronts in super- novae on the largest domain and at the finest spatial resolution studied to date. These simulations were performed on the Intel ASCI-Red machine at Sandia National Laboratories using FLASH, a code developed at the Center for Astrophysical Thermonuclear Flashes at the University of Chicago. FLASH is a modular, adaptive mesh, parallel simulation code capable of handling compressible, reactive fluid flows in astrophysical environments. FLASH is written primarily in Fortran 90, uses the Message-Passing Interface library for inter-processor communication and portability, and employs the PARAMESH package to manage a block-structured adaptive mesh that places blocks only where resolution is required and tracks rapidly changing flow features, such as detonation fronts, with ease. We describe the key algorithms and their implementation as well as the optimizations required to achieve sustained performance of 238 GFLOPS on 6420 processors of ASCI-Red in 64 bit arithmetic.

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.

The Convex SPP-1000 is the first commercial implementation of a new generation of scalable shared memory parallel computers with full cache coherence. It employs a hierarchical structure of processing communication and memory name-space management resources to provide a scalable NUMA environment. Ensembles of 8 HPPA-RISC7100 microprocessorsemploy an internal cross-bar switch and directory based cache coherence scheme to provide a tightly coupled SMP.Up to 16 processing ensembles are interconnected by a 4 ring network incorporating a full hardware implementation of the SCI protocol for a full system configuration of 128 processors. This paper presents the findings of a set of empirical studies using both synthetic test codes and full applications for the Earth and space sciences to characterize the performance properties of this new architecture. It is shown that overhead and latencies of global primitive mechanisms, while low in absolute time, are significantly more costl...