HDF4 is a library and multi-object file format for storing and managing data
between machines. HDF4 is a very different technology than HDF5. The HDF Group
recommends that, other than for working with existing HDF4 data, new
applications use HDF5 since HDF5 addresses important deficiencies of HDF4.

Although The HDF Group maintains HDF4 by fixing defects and porting it to new
operating environments, there is no longer any new development occurring. HDF4
is considered deprecated and new products should be developed in HDF5.
