The '''Advanced Disc Filing System''' (ADFS) is a computing file system particular to the [[Acorn Computers Ltd|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.<ref>http://acorn.chriswhy.co.uk/docs/Acorn/Manuals/Acorn_ADFSUG.pdf</ref>
Acorn's original [[Disc Filing System]] was rather limited into that few31 files couldper bedisk stored on a disksurface, and7 directorycharacters andper file names were restricted to a minimum of 1name and a maximumsingle ofcharacter 7for characters.directory Thenames, Disca Filingformat System'sinherited limitations were in part due to its basis on the disc firmware used infrom the earlier Acorn Atom and System 3–5 [[Eurocard (printed circuit board)|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 <code>$</code> now indicated the hierarchical root of the filesystem. "<code>^</code>" (minus the quotes) was used to refer to the parent directory and "<code>\</code>" 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.<ref>[Acorn User October 1986 - Review - Page 17]</ref>
