Parallel Virtual Machine (PVM) [16] is a software system that permits a network of heterogeneous Unix computers to be used as a single large parallel computer. Thus large computational problems can be solved by using the aggregate power of many computers. Applications, which may be written in Fortran 77, C or C++, can be parallelized by using message-passing constructs common to most distributed-memory computers. By sending and receiving messages, multiple tasks of an application can cooperate to solve a problem in parallel.