D64 File Structure was developed by Miha Peternel for use in C64S.

D64 file contains all sectors as they appear on the 1541 formatted disk.
Each sector is 256 bytes long. Error information (1 byte per sector)
can be added in the end of file.

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  File types currently supported

  174848 bytes = 35 tracks
  175531 bytes = 35 tracks + 683 bytes error information
  196608 bytes = 40 tracks
  197376 bytes = 40 tracks + 768 bytes error information

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  Track sizes

  Tracks, size
    1-17   21 sectors * 256 bytes
   18-24   19 sectors * 256 bytes
   25-30   18 sectors * 256 bytes
   31-35   17 sectors * 256 bytes
  *36-40*  17 sectors * 256 bytes

  Tracks 36-40 are non-standard.

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  Actual layout for 35 track image

  Offset, size, description
   0*256, 256   track 1, sector 0
   1*256, 256   track 1, sector 1
   ...
  20*256, 256   track 1, sector 20
  21*256, 256   track 2, sector 0
   ...
 682*256, 256   track 35, sector 16
 683*256, 683   error info (byte per sector in the same order)


C64S 2.5 introduces NewD64 format of D64 files. The format is still
under construction, so the description is not available yet. It will
be formally published with C64S 3.0.