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Versions
There are two main versions of the HDF library: HDF4 and HDF5. These two versions are not compatible and support for both will continue. However, the support for HDF4 will be limited to bug-fixes and building and testing on new platforms; no new features will be added. There are also two main versions of HDF-EOS that are based on the HDF libraries. HDF-EOS2.x versions are based on HDF4 and HDF-EOS5.x versions are based on HDF5. There are no HDF-EOS3 or HDF-EOS4 versions.
HDF5 was developed to handle very large datasets (> 2GB), parallel processing environments, data that span multiple computing environments, new data models and more complex visualization and analysis. HDF4 supports only datasets smaller than 2 gigabytes, with fewer than 20,000 datasets in any one file, and is not capable of efficiently performing I/O in parallel computing environments.
Comparison of HDF4 and HDF5 Features
(Source: The HDF Group HDF vs. HDF5 web page Retrieved from https://support.hdfgroup.org/products/hdf5_tools/h4toh5/h4vsh5.html)
| HDF5 | HDF4 (4.x and previous releases) |
| Can handle files over 2GB | - |
| No limit on the number of objects | Max limit is 20000 objects and sometimes less |
| One flexible data model | Several rigid data models |
| Supports parallel I/O | Minimal parallel I/O support |
| Threadsafe (designed to be) | - |
| Supports multi-dimensional array of compound datatypes | Supports only 1-dimensional array of compound datatypes |
| Supports variable length datatypes | - |
| Supports references to objects (?) | - |
| Supports "mounting" of files | - |
| Supports hard/soft links -makes delete/move objects easy | - Difficult to do |
| Can flush data immediately | - |
| Extensive datatype/datatype conversion support | More restricted |
| Virtual File layer | - |
| Performance tuning - lots of things | Minimal |
| Ability to register your own compression methods | - |
| Supports multiple unlimited dimensions | Supports 1 unlimited dimension |
| Supports complex subsetting features | Supports basic subsetting features |
| True hierarchical file structure | "pseudo-flat" file structure using vgroups |
| More metadata support | Metadata support |
| Can convert to/from XML | - |
For a comprehensive list of differences and a list of available documents on this topic, please visit The HDF Group's FAQ web page.
Last modified: 02/18/2021