Anex86 PC98 floppy image

Revision as of 14:38, 16 February 2024

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.

fddtype values:

   0x10         1MB/640KB    2DD
   0x30 0xb0    1.44MB       2HD
   0x50 0xd0    320KB        2D
   0x70 0xf0    640KB        2DD
   0x90         1.2MB        2HD

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).

Software

• PC98 Disk Tools
• DiskExplorer
• https://gitlab.com/bunnylin/98ripper

Examples

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

Sample files

• dexvert samples — archive/anex86FDI