I/O continues to be one of the main bottlenecks for scientificapplications. Here are two software packages that many applicationdevelopers use to manage input/output of heterogeneous types of binaryapplication data used on many different platforms. HDF5 and NETCDFare both implemented on top of MPI‐IO and have gained popularity asalternatives to basic POSIX API. HDF5 is a machine-independent andself-documenting file format. Each HDF5 file "looks" like a directorytree, with subdirectories, and leaf nodes that contain the actualdata. This means that data can be found in a file by referring to itsname, rather than its location in the file. NetCDF is a file formatand support library developed at the National Center for AtmosphericResearch (NCAR). Like HDF5, NetCDF is self-describing and portableacross platforms.