TR-DOS filesystem

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The filesystem described here is used with Technology Research Ltd's Beta Disc and Beta 128 Disc disk interfaces. The TR-DOS operating system uses this filesystem.

Floppy disks formatted to 16 sectors per track, with 256-byte sectors. Either single-sided or double-sided disks may be used, and 40 or 80 tracks may be used per side.

The first track of the disk (h0t0s1..h0t0s15) contains the file descriptors (h0t0s1..h0t0s8) and the disk info (h0t0s9). The remaining space on this track is unused.

Space from h0t1s1 on a single sided disk or from h1t0s1 on a double sided disk can be allocated to files. The files are not fragmented.

File descriptor format

A file descriptors are 16 bytes length, so a disk can hold maximum 128 files (8×256/16). The maximum size of a file is 65535 byte.

Offset (dec) Offest (hex) Length (dec) Description
0 0x00 8 Filename, padded with spaces. (If first byte is 0x01 then file is deleted.)
8 0x08 1 File type (extension)
9 0x09 2 File start address little-endian format
11 0x0b 2 File length in bytes
13 0x0c 1 File length in sectors
14 0x0e 1 Starting sector
15 0x0f 1 Starting (logical) track

Note: logical track numbering schema for double sided disks: 0 - h0t0, 1 - h1t0, 2 - h0t1 ... 79 - h1t39, 80 - h0t40 ... 159 - h1t79.

File types

  • B: Basic
  • C: Code
  • D: Data (array variable)
  • #: Sequential or Random access file

Disc information

Information for disc is stored at h0t0s9:

Offset (dec) Offest (hex) Length (dec) Description
0 0x00 1 :=0 - Signals end of catalogue (?)
1 0x01 224 Unused (filled with zero - 0x00)
225 0xe1 2 First free sector address sec:track
227 0xe3 1 Disk type (0x16..0x19)
228 0xe4 1 Number of files on disk
229 0xe5 2 Number of free sectors on disk
231 0xe7 1 :=0x10 - TR-DOS ID
232 0xe8 1 Unused: 0x00
233 0xe9 9 Unused: 0x20 (space)
243 0xf3 1 Unused: 0x00
244 0xf4 1 Number of deleted files on disk
245 0xf5 8 Disk label
253 0xfd 3 End of disk info, filled with 0x00 (Unused?)

Disk types

  • 0x16: 80 tracks, double side
  • 0x17: 40 tracks, double side
  • 0x18: 80 tracks, single side
  • 0x19: 40 tracks, single side

See also

  • TRD format, a disk image format typically used for images of TR-DOS filesystems
  • SCL format, a compact representation of TR-DOS filesystem content

External links