YaPaDOS is patch for AMSDOS and ParaDOS that allows to redirect disk access to harddisk. This is done to keep highest possible compatibility, so only 20 bytes of RAM are used (including 6 used by PARADOS).
Using only 20 bytes of RAM makes impossible features like FAT32 and support for .DSK files, so the disk has special formatting using IDEDOS structures (by Garry Lancaster).