Disc Filing System
| Developer(s) | Acorn Computers |
|---|---|
| Full name | Disc Filing System |
| Introduced | 1982 with Acorn MOS |
| Partition identifier | None |
| Structures | |
| Directory contents | Single catalogue of 31 fixed length records |
| File allocation | Start-Length entries |
| Bad blocks | None |
| Limits | |
| Max. volume size | 256 KB |
| Max. file size | 255½ KB |
| Max. number of files | 31 |
| Max. filename length | 7 characters |
| Allowed characters in filenames | ASCII |
| Features | |
| Dates recorded | None |
| Date range | N/A |
| Forks | No |
| Attributes | Directory character, Load address, Execution address, Locked |
| File system permissions | No |
| Transparent compression | No |
| Transparent encryption | No |
| Other | |
| Supported operating systems | Acorn MOS |
The Disc Filing System (DFS) is a computer file system developed by Acorn Computers, initially as an add-on to the Eurocard-based Acorn System 2.
In 1981, the Education Departments of Western Australia and South Australia announced joint tenders calling for the supply of personal computers to their schools. Acorn's Australian computer distributor, Barson Computers, convinced Joint Managing Directors Hermann Hauser and Chris Curry to allow the soon to be released Acorn BBC Microcomputer to be offered with disk storage as part of the bundle. They agreed on condition that Barson adapted the Acorn DFS from the System 2 without assistance from Acorn as they had no resources available. This required some minor hardware and software changes to make the DFS compatible with the BBC Micro.
Barson won the tenders for both states, with the DFS fitted, a year ahead of the UK. It was this early initiative that resulted in the BBC Micro being more heavily focused on the education market in Australia, with very little penetration of the home computer market until the arrival of the Acorn Electron.
The DFS shipped as a ROM and Disk Controller Chip fitted to the BBC Micro's motherboard. The filing system was of extremely limited functionality and storage capability, using a flat directory structure. Each filename can be up to seven letters long, plus one letter for the directory in which the file is stored.
The DFS is remarkable in that unlike most filing systems, there was no single vendor or implementation. The original DFS was written by Acorn, who continued to maintain their own codebase, but various disc drive vendors wrote their own implementations. Companies who wrote their own DFS implementations included Cumana, Opus and Watford Electronics. The Watford Electronics implementation is notable for supporting 62 files per disc instead of the usual 31, using a non-standard disc format. Other features in third-party implementations included being able to review free space, and built-in FORMAT and VERIFY commands, which were shipped on a utility disc with the original Acorn DFS.
Acorn followed up their original DFS series with the Acorn 1770 DFS, which used the same disc format as the earlier version but added a set of extra commands and supported the improved WD1770 floppy drive controller chip.
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