FDF Image

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Basically FDF used RLE compression.
 
Basically FDF used RLE compression.
  
−
if first byte is 0xFF then its end of block, if byte is 0x00 then remainder is stored uncompressed. Otherwise if b7 is set then the lower 7 bits are the repeat count and the next byte is the byte to repeat. If b7 is zero then its a store count, followed by the stored bytes.
+
Integers are stored as little-endian.
 +
 
 +
EZ disklone truncates the image, the unused sectors filled with 0xF6 at end of the disk are not stored.
 +
 
 +
//------------------------------------------------------------------------------
 +
// File header
 +
//------------------------------------------------------------------------------
 +
 +
// file signature
 +
#define FDFFILE_SIGNATURE  MAKE_FOURCC(0x1A, 'F', 'D', 'F')
 +
 +
// file header
 +
// - 128 bytes
 +
typedef struct
 +
{
 +
  // equal to FDFFILE_SIGNATURE
 +
  UINT32 Signature;
 +
 +
  // unknown (0x0600)
 +
  UINT16 Unknown1;
 +
 +
  // description
 +
  CHAR  Descr[FDFFILE_LEN_DESCR];
 +
 +
  // all zero
 +
  BYTE  Reserved1[8];
 +
 +
  // unknown (0x0100)
 +
  UINT16 Unknown2;
 +
 +
  // unknown (0x0034)
 +
  UINT16 Unknown3;
 +
 +
  // all zero
 +
  BYTE  Reserved2[46];
 +
 +
  //
 +
} TFdfFile_FileHdr;
 +
 +
 +
//------------------------------------------------------------------------------
 +
// Block header
 +
//------------------------------------------------------------------------------
 +
 +
// block compression method
 +
#define FDFFILE_METHOD_STORED  0x00
 +
#define FDFFILE_METHOD_RLE      0x01
 +
#define FDFFILE_METHOD_EOD      0xFF   /* end of data */
 +
 +
// default block size is 9216 bytes
 +
#define FDFFILE_DEFAULT_BLKSIZE  (9*SIZE_KB)
 +
 +
 +
// block header
 +
// - 5 bytes
 +
// - followed by RLE compressed data
 +
typedef struct
 +
{
 +
  // one of FDFFILE_METHOD_xxx
 +
  UINT8  Method;
 +
 +
  // CRC16L checksum (LHA)
 +
  UINT16 CRC;
 +
 +
  // number of compressed bytes
 +
  UINT16 Size;
 +
 +
  //
 +
} TFdfFile_BlkHdr;
 +
 +
 +
 +
//------------------------------------------------------------------------------
 +
// RLE compression
 +
//------------------------------------------------------------------------------
 +
// - if FDFFILE_METHOD_EOD    then its end of data
 +
// - if FDFFILE_METHOD_STORED then remainder is stored uncompressed
 +
// - Otherwise:
 +
//  * if b7 is set then the lower 7 bits are the repeat count and the next
 +
//    byte is the byte to repeat
 +
//  * If b7 is zero then its a store count, followed by the stored bytes
 +
//------------------------------------------------------------------------------
 +
// - decompressed blocks do not need to be the same size as stored blocks
 +
//  (stored blocks are FDFFILE_DEFAULT_BLKSIZE in size)
 +
//------------------------------------------------------------------------------
  
 
==Software==
 
==Software==

Revision as of 20:56, 21 September 2026

File Format
Name FDF Image
Ontology
Extension(s) .fdf
Released 1991

Contents

Overview

Floppy Disk File (FDF) are disk images used by the DOS software EZ-DisKlone Plus. Introduced in 1991, the format is a compressed disk image validated by a 16bit CRC.

File Identification

FDF files have the header "1A 46 44 46".

Specifications

The FDF file format is reverse engineered in 86Box, the source code can be found at: 

86Box-master\src\floppy\fdd_img.c

Basically FDF used RLE compression.

Integers are stored as little-endian.

EZ disklone truncates the image, the unused sectors filled with 0xF6 at end of the disk are not stored. 

//------------------------------------------------------------------------------
// File header
//------------------------------------------------------------------------------

// file signature
#define FDFFILE_SIGNATURE   MAKE_FOURCC(0x1A, 'F', 'D', 'F')

// file header
// - 128 bytes
typedef struct
{
  // equal to FDFFILE_SIGNATURE
  UINT32 Signature;

  // unknown (0x0600)
  UINT16 Unknown1;

  // description
  CHAR   Descr[FDFFILE_LEN_DESCR];

  // all zero
  BYTE   Reserved1[8];

  // unknown (0x0100)
  UINT16 Unknown2;

  // unknown (0x0034)
  UINT16 Unknown3;

  // all zero
  BYTE   Reserved2[46];

  //
} TFdfFile_FileHdr;


//------------------------------------------------------------------------------
// Block header
//------------------------------------------------------------------------------

// block compression method
#define FDFFILE_METHOD_STORED   0x00
#define FDFFILE_METHOD_RLE      0x01
#define FDFFILE_METHOD_EOD      0xFF   /* end of data */

// default block size is 9216 bytes
#define FDFFILE_DEFAULT_BLKSIZE   (9*SIZE_KB)


// block header
// - 5 bytes
// - followed by RLE compressed data
typedef struct
{
  // one of FDFFILE_METHOD_xxx
  UINT8  Method;

  // CRC16L checksum (LHA)
  UINT16 CRC;

  // number of compressed bytes
  UINT16 Size;

  //
} TFdfFile_BlkHdr;



//------------------------------------------------------------------------------
// RLE compression
//------------------------------------------------------------------------------
// - if FDFFILE_METHOD_EOD    then its end of data
// - if FDFFILE_METHOD_STORED then remainder is stored uncompressed
// - Otherwise:
//   * if b7 is set then the lower 7 bits are the repeat count and the next
//     byte is the byte to repeat
//   * If b7 is zero then its a store count, followed by the stored bytes
//------------------------------------------------------------------------------
// - decompressed blocks do not need to be the same size as stored blocks
//   (stored blocks are FDFFILE_DEFAULT_BLKSIZE in size)
//------------------------------------------------------------------------------

Software

Sample File

Links

Retrieved from "http://fileformats.archiveteam.org/index.php?title=FDF_Image&oldid=52084"
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