In the original FITS design, intended for half-inch magnetic tape, the end of a file could easily be identified by a tape end-of-file mark. Not all other media support such a clear hardware delimiter. D. Wells has proposed the creation of a FILEMARK extension, which would represent an end-of-file on media where the end of the file cannot easily be marked on the hardware. The name has been reserved for use in developing this concept; as yet there is no detailed proposal.
A FITS file might contain a pure bit stream, such as telemetry. An extension type name DUMP has been proposed and reserved for such data. Details of how this extension would be structured remain to be developed.