p4 is a portable library of C and Fortran subroutines for programming parallel computers. It is the current version of a system that has been in use since 1984. It includes features for explicit parallel programming of shared-memory machines, distributed-memory machines (including heterogeneous networks of workstations), and clusters, by which we mean sharedmemory multiprocessors communicating via message passing. We discuss here the design goals, history, and system architecture of p4 and describe briefly a diverse collection of applications that have demonstrated the utility of p4. 1 Introduction p4 is a library of routines designed to express a wide variety of parallel algorithms portably, efficiently and simply. The goal of portability requires it to use widely accepted models of computation rather than specific vendor implementations of those models. The goal of efficiency requires it to use models of computation relatively close to those provided by the machines themselves and t...

object representing an index space ffl Grid: Uniform dynamic array instantiated over Region ffl XArray: Dynamic array (currently 1 dimensional) of Grids distributed over processors Operators: ffl forall construct that operates over all Grids in a XArray ffl Reduction operators across processors Programming Scheme: ffl Decomposition of computational space into an array of Regions ffl Assignment of each Region to a processor \Gamma ? automatic or user-defined mapping ffl Create an XArray of Grids corresponding to Regions ffl Satisfy data-dependencies using Domain Calculus: ) grow operation on a Region ) copy operation to fill halo ffl Operate on XArray in parallel using forall construct Weak consistency - does not guarantee that a remote access/update is complete when the associated call returns. Explicit synchronization must be used to ensure consistency. Consistency is guaranteed on exit from LPARX's for all loop via an implicit synchronization Department of Computer Sciences & Center for Relativity ffl University of Texas at Austin Austin, TX 78712-1081 A Survey of Existing Support DRAFT LPARX's standard library of partitioners or user-defined.