HDF5 is a completely new Hierarchical Data Format product consisting of a data
format specification and a supporting library implementation. HDF5 is designed
to address some of the limitations of the older HDF product and to address
current and anticipated requirements of modern systems and applications.

HDF5 includes the following improvements:
- A new file format designed to address some of the deficiencies of HDF4.x,
  particularly the need to store larger files and more objects per file.
- A simpler, more comprehensive data model that includes only two basic
  structures: a multidimensional array of record structures, and a grouping
  structure.
- A simpler, better-engineered library and API, with improved support for
  parallel I/O, threads, and other requirements imposed by modern systems
  and applications.

WWW: https://www.hdfgroup.org/