HDF has two interfaces, the SD and the DFSD, that support the scientific data model. In general, the newer, multi-file SD interface should be used instead of the DFSD interface.
Scientific Data Sets (SDSs) are used for storing n-Dimensional gridded data. The actual data in the dataset can be of any of the "standard" number types: 8, 16, and 32-bit signed and unsigned integers, and 32 and 64-bit floating point values. In addition, the SD interface allows SD data sets with variable bit lengths (1 to 32-bits) to be created.
Meta-data such as dimension scales and attributes can be stored with an SDS. With the SD interface, user-defined as well as pre-defined attributes are available. Only pre-defined attributes are available with the DFSD interface.