TRD format

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The TRD format was created for storing Beta Disk (TR-DOS) disk images for emulation.

A variety of Russian Spectrum clones (including the Pentagon and Scorpion) use the TR-DOS disk operating system with a builtin Beta Disk Interface.

This format is member of the Easy Disk Image Formats and contains only the data of sectors.

It is typically used for images of disks using the TR-DOS filesystem.

TRD file structure

TRD images can store single or double sided 40 or 80 track disk images.

File Header

There is no any header or file signature (magic bytes).

Sector layout

Sectors laid from 1st to last within a track:

  • Sector 1
  • Sector 2


  • Sector last

Tracks follow the “alt” schema:

  • Side: 0 Track: 0
  • Side: 1 Track: 0
  • Side: 0 Track: 1


  • Side: 0 Track: 79
  • Side: 1 Track: 79

File length

TR-DOS uses 256 BPS and 16 SPT for disks, so a

  • 40 track 1 sided image length is 163840 byte (1×40×16×256)
  • 40 track 2 sided image length is 327680 byte
  • 80 track 1 sided image length is 327680 byte
  • 80 track 2 sided image length is 655360 byte

Partial images

TRD files may end before the calculated full length if sectors up to the end contains no data.

e.g. Prince of Persia - PRINCE_P.TRD (2 sided 80 track disk image) is only 255488 bytes length, because the last sector which contains data is h0t31s6 (2×31×16+6)×256

See also

SCL format is an alternative storage format for TR-DOS filesystem images. Instead of a TRD image, SCL stores only the directory structure and data of files.

External Links

TR-DOS info from RAMSOFT