Migrating from PVM to MPI.I. The Unify system

This paper presents a new kind of portability system, Unify, which modifies the PVM message passing system to provide (currently a subset of) the message Passing Interface (MPI) standard notation for message passing. Unify is designed to reduce the effort of learning MPI, while providing a sensible means to make use of MPI libraries and MPI calls (while applications continue to run in the PVM environment). We are convinced that this strategy will reduce the costs of porting completely to MPI, while providing a gradual environment within which to evolve. Furthermore, it will permit immediate use of MPI-based parallel libraries in applications, even for those applications that continue to use PVM for message passing. We describe several paradigms for supporting MPI and PVM message passing notations in a single environment, and note related work on MPI and PVM implementations. We show the design options that existed within our chosen paradigm (which is an MPI interface added to the base PVM system) and why we chose that particular approach. We indicate the total evolution path of porting a PVM application to MPI with the help of porting libraries. Finally, we indicate our current directions and planned future work