TR-DOS filesystem

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File Format
Name TR-DOS filesystem
Ontology
Extension(s) .trd
Kaitai Struct Spec tr_dos_image.ksy
TR-DOS is an operating system for ZX Spectrum personal computer with Beta Disc floppy drive interface. Despite being developed by British company Technology Research Ltd, it was not especially popular in the West, but was more popular in USSR and post-USSR in 80-90s.

5¼" and 3½" floppies are used with the following formats:

Number of tracks per side Number of sides Number of tracks (total) Number of sectors Number of bytes
80 2 160 2560 655360
40 2 80 1280 327680
80 1 80 1280 327680
40 1 40 640 163840

.trd files: TR-DOS disk images

Diskettes can be dumped to .trd files, which are plain sector-by-sector headerless dumps (the same idea as /dev/fd0). Each sector is 256 bytes, each track contains 16 sectors. Tracks are arranged in the same order as "logical tracks" in TR-DOS: 0th track on 0th side, 0th track on 1st side, 1st track on 0th side, 1st track on 1st side, …. If remaining sectors at the end of floppy are unused, .trd file can be less than actual floppy size. These files are supported by most ZX Spectrum emulators.

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