RISC OS filetype
RISC OS filetype, or Acorn filetype, is a system of 12-bit file type identifiers used on RISC OS. It is essentially the RISC OS equivalent of a filename extension. A filetype is usually written as three hexadecimal characters, like "FF9".
A number of RISC OS archive formats have a 32-bit "load address" field, and the filetype might be contained in this field. Apparently, if the three high nibbles are all 0xf, then the next three nibbles contain the file type. Formats that have such a field include ArcFS, Spark, Squash, and ZIP (in extra field #0x4341).
Sometimes, when a RISC OS file is transferred to a foreign system, its filetype is appended to the filename, separated with a comma.