TRD Disk Image Format
The TRD format was created for storing Betadisk/TR-DOS disk images for emulation. The Russian Spectrum clones (Pentagon Scorpion) use the TR-DOS disk operating system with builtin Beta Disk interface.
This format is member of the Easy Disk Image Formats and contains only the data of sectors.
TRD file structure
TRD images can store single or double sided 40 or 80 track disk images.
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 follow the “alt” schema:
- Side: 0 Track: 0
- Side: 1 Track: 0
- Side: 0 Track: 1
- Side: 0 Track: 79
- Side: 1 Track: 79
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
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