Efficient Communication on MPPs and NOWs

			   David E. Culler
		  University of California, Berkeley

The communication hardware of Massively Parallel Processors has
advanced dramatically over the past decade and parallel language
implementation has matured, yet the predominant communication software
layers have evolved only slightly.  Recently, Active Messages
highlighted this divergence in demonstrating a substantial reduction
in communication overhead with simple primitives that fully utilize
available hardware.  Simple primitives also give the compiler greater
control and wider scope for optimization.  The communication hardware
of Networks of Workstations (NOWs) is about to take a dramatic step
forward as well, so the opportunity exists to establish efficient
communication layers in both regimes.  In this talk, I will describe
the engineering of a fast Active Message layer for current MPPs and
examine the opportunities and pitfalls of emerging NOWs.