Pvm and Mpi Are Completely Diierent

PVM and MPI are often compared. These comparisons usually start with the un-spoken assumption that PVM and MPI represent diierent solutions to the same problem. In this paper we show that, in fact, the two systems often are solving diierent problems. In cases where the problems do match but the solutions chosen by PVM and MPI are diierent, we explain the reasons for the diierences. Usually such diierences can be traced to explicit diierences in the goals of the two systems, their origins, or the relationship between their speciications and their implementations. For example, we show that the requirement for portability and performance across many platforms caused MPI to chose diierent approaches than PVM, which is able to exploit the similarities of network-connected systems. This paper expands on earlier discussions; among the additions are parallel I/O, the safety of contexts, and a subtle performance issue in multiparty communications.