\abstracts{
High-end, mainstream symmetric multiprocessor (SMP) computers are beginning
to offer numerical modelers realistic alternatives to traditional vector or
massively parallel processing (MPP) supercomputers.  We report on the
implementation of the MIT ocean-atmosphere dynamical kernel on a DEC 8400
SMP.  The SMP implementation is contrasted with an existing optimized
version of the same model on the CM-5 parallel vector supercomputer.  We
discuss the numerical methods and programming styles appropriate to the two
machines.  To characterize the differences in the architectures, we compare
the performance of key kernels of the model which are typical of those in
many computational fluid dynamics (CFD) codes.  To render the model readily
accessible to individual researchers and students, it is written in High
Performance Fortran, which emphasizes both high performance and a
high-level programming environment.  Our study highlights cache memory
architecture and compilation systems as particularly critical technologies
in determining the overall utility of a mainstream SMP system for the
oceanographic and meteorological community.  Notwithstanding these caveats,
we demonstrate that the performance of ``high-end mainstream'' SMP's is
rapidly converging on that of ``low-end'' computer center facilities for
real scientific applications.  }
