www.riscos.com Technical Support:
Under RISC OS 3.5 and earlier a DOSFS image file had a maximum size of 32 MB. This limit was imposed by the DOS boot block used in laying out the image file.
RISC OS 3.6 uses a newer type of DOS boot block which removes this restriction.
Under RISC OS 3.6 and later, DOSFS is less stringent in its checking of DOS formats. Some discs that earlier versions of DOSFS rejected are now accepted. In particular DOSFS no longer checks for two FATs, and will accept discs that have just one FAT.