Advanced Disc Filing System
| Developer(s) | Hugo Tyson, Nick Reeves (Acorn Computers) |
|---|---|
| Full name | Advanced Disc Filing System |
| Introduced | 1983 with Acorn MOS |
| Partition identifier | Hugo or Nick (Directory header/footer) |
| Structures | |
| Directory contents | Hierarchical fixed-length tables |
| File allocation | One range per file plus table of free-space ranges (L), bitmap with embedded file IDs (E) |
| Bad blocks | none (L), marked in bitmap (E) |
| Limits | |
| Max. volume size | 512 MiB |
| Max. file size | 512 MiB |
| Max. number of files | 47 per directory (L), 77 per directory (E) |
| Max. filename length | 10 characters |
| Allowed characters in filenames | ASCII (Acorn MOS), ISO 8859-1 (RISC OS) |
| Features | |
| Dates recorded | Modification |
| Date range | 1 January 1900 - 3 June 2248 |
| Date resolution | 10 ms |
| Forks | no |
| Attributes | Load address, execute address and file cycle number (Acorn MOS); File type and modification time (RISC OS); User read/write/execute-only; public read/write/execute-only; Deletion lock |
| File system permissions | None |
| Transparent compression | No |
| Transparent encryption | No |
| Data deduplication | No |
| Other | |
| Supported operating systems | Acorn MOS, RISC OS |
The Advanced Disc Filing System (ADFS) is a computing file system particular to the Acorn computer range and RISC OS-based successors. Initially based on the rare Acorn Winchester Filing System, it was renamed to the Advanced Disc Filing System when support for floppy discs was added (utilising a WD1770 floppy disc controller) and on later 32-bit systems a variant of a PC-style floppy controller.
Acorn's original Disc Filing System was limited to 31 files per disk surface, 7 characters per file name and a single character for directory names, a format inherited from the earlier Atom and System 3–5 Eurocard computers. To overcome some of these restrictions Acorn developed ADFS. The most dramatic change was the introduction of a hierarchical directory structure. The filename length increased from 7 to 10 letters and the number of files in a directory expanded to 47. It retained some superficial attributes from DFS; the directory separator continued to be a dot and $ now indicated the hierarchical root of the filesystem. ^ was used to refer to the parent directory, @ the current directory, and \ was the previously-visited directory.
The BBC Master Compact contained ADFS Version 2.0, which provided the addition of format, verify and backup commands in ROM.
ADFS on 8-bit systems required a WD1770 or later 1772-series floppy controller, owing to the inability of the original Intel 8271 chip to cope with the double-density format ADFS required. ADFS could however be used to support hard discs without a 1770 controller present; in development the use of hard discs was the primary goal, extension to handle floppies came later. The 1770 floppy controller was directly incorporated into the design of the Master Series and B+ models, and was available as an 'upgrade' board for the earlier Model B. The Acorn Electron's floppy interface (Acorn Plus 3) was an add-on unit, initially available through Acorn and later Pres (aka Advanced Computer Products). The ACP implementation of ADFS fixed a flaw in the Acorn version v1.0, that required the use of a file named ZYSYSHELP. On the Electron, Disk corruption could also occur if attempting to use the *COMPACT command without disabling the blinking cursor. This was due to the fact that the *COMPACT command used screen memory as working space during the operation, and the blinking cursor corrupted that memory space.
ADFS supported hard discs, and 3½" floppy discs formatted up to 640 KB capacity using double density MFM encoding (L format; single-sided disks were supported with the S format (160 KB) and M format (320 KB)). ADFS as implemented in the BBC microcomputer system (and later RISC OS) never had support for single-density floppies.
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