Advanced Disc Filing System

ADFS
Developer(s)Hugo Tyson, Nick Reeves (Acorn Computers)
Full nameAdvanced Disc Filing System
Introduced1983; 41 years ago (1983) with Acorn MOS
Partition IDsHugo or Nick (Directory header/footer)
Structures
Directory contentsHierarchical fixed-length tables
File allocationOne range per file plus table of free-space ranges (L), bitmap with embedded file IDs (E)
Bad blocksnone (L),[1] marked in bitmap (E)
Limits
Max volume size512 MB
Max file size512 MB
Max no. of files47 per directory (L), 77 per directory (E)
Max filename length10 characters
Allowed filename
characters
ASCII (Acorn MOS), ISO 8859-1 (RISC OS)
Features
Dates recordedModification
Date range1 January 1900 - 3 June 2248
Date resolution10 ms
Forksno
AttributesLoad 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 deduplicationNo
Other
Supported
operating systems
Acorn MOS, RISC OS

The Advanced Disc Filing System (ADFS) is a computing file system unique 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 (using a WD1770 floppy disc controller) and on later 32-bit systems a variant of a PC-style floppy controller.[2]

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, but omitted support for hard discs.[3]

  1. ^ Cite error: The named reference reeves-efmt was invoked but never defined (see the help page).
  2. ^ Advanced Disc Filing System: User Guide (PDF). Acorn Computers Limited. September 1985. Retrieved 1 August 2016.
  3. ^ "Taking the lid off the Master Compact". Acorn User. October 1986. p. 17. Retrieved 5 September 2020.