MPI-IO was developed in 1994 in the IBM's Watson Laboratory in order to provide parallel I/O support for MPI. NASA adopted MPI-IO for its own research computing projects in 1996 and in the same year MPI Forum decided to incorporate MPI-IO in MPI-2 . And so, when MPI-2 was published in 1997, MPI-IO was already in it.
MPI-IO provides relatively simple, yet high performance, abstractions for parallel IO. It allows parallel access to single files from multiple processes.