Message Passing Interface (MPI)

MPI is a specification for the developers and users of message passing libraries. By itself, it is NOT a library - but rather the specification of what such a library should be.
Simply stated, the goal of the Message Passing Interface is to provide a widely used standard for writing message passing programs. The interface attempts to be

• practical
• portable
• efficient
• flexible

Reasons for Using MPI:

• Standardization - MPI is the only message passing library which can be considered a standard. It is supported on virtually all HPC platforms. Practically, it has replaced all previous message passing libraries.
• Portability - There is no need to modify your source code when you port your application to a different platform that supports (and is compliant with) the MPI standard.
• Performance Opportunities - Vendor implementations should be able to exploit native hardware features to optimize performance. 
• Functionality - Over 115 routines are defined in MPI-1 alone.
• Availability - A variety of implementations are available, both vendor and public domain.