1.3. Product description
The MPT package contains the following components:
Optimized implementations of the Message Passing Interface (MPI) for UNICOS systems and UNICOS/mk systems. These implementations are based on the MPI 1.2 specification from the Message Passing Interface Forum. They support high-speed communications among the processors on each system. The implementation on UNICOS/mk also supports a subset of the MPI-2 specification. The implementation on UNICOS systems supports high-speed communications between UNICOS systems of like architecture.
An optimized version of Parallel Virtual Machine (PVM) for UNICOS systems and UNICOS/mk systems. This version is based on Oak Ridge National Laboratories (ORNL) version 3.3.10. It supports high-speed communications among the processors on each system. It also supports high-speed communications between heterogeneous systems.
Caution 
MPT 1.4 will be the last release in which PVM will be supported.
Logically shared, distributed memory (SHMEM) message passing capability using the shmem_get(3) and shmem_put(3) functions on UNICOS systems. (SHMEM on UNICOS/mk systems is delivered with CrayLibs.) This high-performance library supports communications among the processors on each system.
MPI is a standard specification for message passing libraries, allowing portable message passing programs in the Fortran and C languages. MPI was created by the Message Passing Interface Forum (MPIF). MPIF is not sanctioned or supported by any official standards organization. Its goal was to develop a widely used standard for writing message passing programs. The implementation of this standard includes a library (libmpi.a), a run-time command (mpirun(1)), and a library that allows profiling of message passing applications (libpmpi.a). On UNICOS systems, the profiling functionality is included in libmpi.a.
PVM is a software project that was developed jointly by Oak Ridge National Laboratories (ORNL), the University of Tennessee, and Emory University. PVM consists of a main library, a user-level daemon (pvmd3), a console (pvm(1)), and some additional commands and libraries. The main PVM library name is libpvm3.a.
The PVM and MPI libraries provide communications and synchronization functions that are necessary for writing distributed applications. For example, you can add calls that cause one task to send a message to another, or to receive a message, or to wait until another task is finished. The PVM software supports heterogeneous systems by automatically converting data. The MPI software is supported between UNICOS systems of the same architecture and within a partition on UNICOS/mk systems.
SHMEM message passing is another form of distributed programming. It differs from PVM and MPI message passing in that it uses one-sided communication (that is, one processing element (PE) on a Cray T3E system can send or receive data from another PE without the knowledge of that PE).
To use PVM, MPI, or SHMEM message passing directly, you must change your source code to add the appropriate calls.
MPI support for Cray T3D systems is provided through a third-party product available from Edinburgh Parallel Computing Centre (EPCC).