PIOFS  is the parallel file system on the IBM SP-2. In addition to a Unix-like read/write interface, PIOFS also supports logical partitioning of files. A processor can independently specify a logical view of the data in a file, called a subfile, and then read/write that subfile with a single call. It is straightforward to implement the Unix-like interface of PIOFS on top of ADIO. The logical file views of PIOFS can be mapped to appropriate MPI derived datatypes and accessed by using the noncontiguous read/write calls of ADIO.