Anex86 PC98 floppy image

The FDI disk image format for NEC PC-98 disk images seems to originate from the Anex86 PC98 emulator.

FDI File Header

The FDI header is 4096 bytes long, Intel little-endian, and starts with this 32-byte header.

   typedef struct {
       BYTE   dummy[4];
       BYTE   fddtype[4];
       BYTE   headersize[4];
       BYTE   fddsize[4];
       BYTE   sectorsize[4];
       BYTE   sectors[4];
       BYTE   surfaces[4];
       BYTE   cylinders[4];
   } FDIHDR;

The next 4,064 bytes of the header seem to always be pad bytes.

FDI file image contents

The remaining portion of the file is a raw dd-style image of the disk. In the case of an HDM image, you can prepend a 4096-byte header onto the image to turn it into an FDI (see example below).

Examples

For a 1261568-byte "2HD" disk image (like *.HDM format), the header is as follows: