The Advanced Disc Filing System (ADFS) is a computing file system particular to the Acorn computer range introduced in the disc drive add-on for the Acorn Electron. It could be added to the BBC B if an Acorn 8271 or 1770 adaptor board was fitted and to a B+ without adding any extra controller chips. A version of it was later incorporated directly into the BBC Master and all later models. The Linux kernel has support for this format.

Acorn's original Disc Filing System was very limited in that very few files could be stored on a disk, and directory and file names were restricted to 1 and 7 characters respectively.

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 and \ was the previously visited directory. It supported 3½" floppy discs, formatted up to 640k capacity using double density MFM encoding.

Later, RISC OS would add a per-file "type" attribute; 12 bits of type information that was used to denote the contents or intended use of a file. This can be thought of as being similar to the type attributes stored in Apple's HFS file system, only with much less information. Later editions of ADFS supported 800k double density floppies along with 77 entries per directory, and 1600k high density floppies. It was also used as the hard disc filesystem on the "winchester" hard drives for the BBC micro and later on the hard drives for the Acorn Archimedes and Risc PC models.

External link

• ADFS on disk layout documentation

Acorn Computers | Disk file systems | Disk operating systems

Acorn Disc File System