OPD format

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OPD Disk Image Format

The OPD format was created for storing Opus Discovery disk images for emulation.

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

OPD files sometimes have .opu extension.

OPD file structure

OPD images can store single or double sided 40 track disk images, but most of the files are single sided 40 track disk images.

File Header

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


Sectors laid from 1st to last within a track:

  • Sector 1
  • Sector 2


  • Sector last

Tracks in file

Track data follow the “alt” schema:

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


  • Side: 0 Track: 39
  • Side: 1 Track: 39

File length

Opus Discovery uses 256 BPS and 18 SPT for disks (see Opus Discovery), so a

  • 40 track 1 sided image length is 184320 byte (1×40×18×256)
  • 40 track 2 sided image length is 368640 byte