Kappa applications can process NDFs in one or more of the following HDS data types. The correspondence between Fortran types and HDS data types is as follows:
| HDS Type | Number of bytes | FORTRAN Type |
| _DOUBLE | 8 | DOUBLE PRECISION |
| _INTEGER | 4 | INTEGER |
| _INT64 | 8 | INTEGER*8 (non-standard) |
| _REAL | 4 | REAL |
| _UBYTE | 1 | BYTE |
| _BYTE | 1 | BYTE |
| _UWORD | 2 | INTEGER*2 |
| _WORD | 2 | INTEGER*2 |
(_UBYTE) and (_UWORD) types are unsigned and so permit data ranges of 0–255 and 0–65535 respectively.