Disk Files
                                 ==========

 .DSK Generic disk image format, used for +3 disks by x128, xzx and others.
 .FDI Image of a TR-DOS disk, used by UKV Spectrum Debugger.
 .TRD Image of a TR-DOS disk, used by x128, xzx and others.


                        .DSK (x128, xzx v2 & others)
                        ----------------------------

See the specification at Kevin Thacker's Unofficial Amstrad WWW Resource
(.DSK files were originally used on some of the Amstrad CPC emulators).


                     [NEW] .FDI (UKV Spectrum Debugger)
                     ----------------------------------

[Translated from UKV Spectrum Debugger's documentation by Mac Buster]

   Offset   Field size    Description

    0x00       0x03       Text "FDI"
    0x03       0x01       Write protection (0: write enabled; 1: disabled)
    0x04       0x02       Number of cylinders
    0x06       0x02       Number of heads
    0x08       0x02       Offset of disk description
    0x0A       0x02       Data offset
    0x0C       0x02       Length of additional information in header. (UKV
                          uses 00)
    0x0E       (x)        Additional information; length is specified in
                          the previous field.
    0x0E+(x)              Track headers area. This section contains all
                          information on the disk format. This area must
                          contain at least "Number of cylinders"*"Number
                          of heads" headers. The headers are stored in the
                          sequence Cyl 0 Head 0; Cyl 0 Head 1; Cyl 1 Head
                          0 etc.
   (Description offset)   A description of the disk terminated with 0x00
                          can be placed here; the MAKEFDI utility
                          (supplied by UKV) allows for up to 64
                          characters, including the terminating null.
   (Data offset)          The actual disk data. The size and sequence
                          depends on the disk format.

                            Track header format

   Offset   Field size    Description

    0x00       0x04       Track offset: the offset of the track data,
                          relative to the data offset defined above.
    0x04       0x02       (Always 0x0000)
    0x06       0x01       Number of sectors on this track.
    0x07   (Sectors*7)    Sector infomation:
                          Bytes 00-03 give the cylinder number, head
                          number, sector size (00: 128 bytes; 01: 256; 02:
                          512; 03: 1024; 04: 4096) and sector number
                          respectively.
                          Byte 04 contains the flags:
                            Bits 0-5 are CRC marks: if the CRC was correct
                            for a sector size 128, 256, 512, 1024, 2048 or
                            4096, then the respective bit will be set. If
                            all bits are 0 then there was a CRC error when
                            this sector was written.
                            Bit 6 is always 0.
                            Bit 7 is 0 for normal data, or 1 for deleted
                            data.
                          Bytes 05-06 give the sector offset, relative to
                          (data offset+track offset)
   7*(Sectors+1)          Track header length

Note that UKV 1.2 does not use the flag byte.

                        .TRD (x128, xzx v2 & others)

See the TR-DOS System Info from World Wide Ramsoft.