Acorn System Disk File System / Atom DOS

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: