Discs for the System series have an identical catalogue format to those for the BBC Micro, except all entries are in a directory " " (space), disks do not have a cycle number, and files do not have bits 16 and 17 of load and execution addresses.
The places they would occupy are reserved and must be cleared. A BASIC program named DCONV, on the Utility disc, performs this task.
Catalog format
The disk layout is identical to Acorn DFS with some differences shown below:
| Byte | Track 0 Sector 0 | Track 0 Sector 1 | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ||
| 0 | First 8 characters of volume title padded with NULs or spaces | Last 4 characters of volume title padded with NULs or spaces | |||||||||||||||
| 1 | |||||||||||||||||
| 2 | |||||||||||||||||
| 3 | |||||||||||||||||
| 4 | Reserved | ||||||||||||||||
| 5 | Number of files | ||||||||||||||||
| 6 | Boot Opts | 98 | |||||||||||||||
| 7 | 7 | Sectors in volume | 0 | ||||||||||||||
| 8 | File name padded with spaces | 7 | Load address | 0 | Last file | ||||||||||||
| 9 | 15 | 8 | |||||||||||||||
| 10 | 7 | Execution address | 0 | ||||||||||||||
| 11 | 15 | 8 | |||||||||||||||
| 12 | 7 | File length | 0 | ||||||||||||||
| 13 | 15 | 8 | |||||||||||||||
| 14 | Reserved | 17 16 | Reserved | 9 8 | |||||||||||||
| 15 | Lk. | Ascii Space (0x20, 32) | 7 | Start sector | 0 | ||||||||||||
Differences between Acorn DFS and System DFS
- The Reserved entries must be clear.
- The disk type in bits 2 and 3 of sector 1 byte 6 must be clear as with DFS.
- Lk. in byte 7 is the same as for Acorn DFS
Sources
This section is based loosely on the following:
- Acorn DFS disk format - beebwiki.mdfs.net
- Acorn, Watford, Solidisk and Duggan DFS Filesystem Structure mdfs.net