Advanced Disc Filing System

In computing, ADFS stands for the Advanced Disc Filing System. It is peculiar to the Acorn computer range, although a Linux filesystem exists to read filesystems in this format.

Acorn's original DFS was an extremely limited design in order to make best use of the 100k floppy discs it was originally designed for. It had a flat directory structure with one letter to represent the current directory ($ by default). Changing directory meant using a different letter as the prefix. You could refer to a file in a different directory by prefixing it with the letter and a dot, eg "A.LETTER". Names could be up to 7 letters long, plus one letter for the directory. The file table was one disc sector, limiting the number of files on the disc to 31.

Other companies, including Watford Electronics sold their own replacement DFS. They typically added extensions, such as permitting two sectors to be used for the directory, increasing the maximum number of files to 62.

The Advanced Disc Filing System was a dramatic change. It was hierarchical and expanded the filename length from 7 to 10 letters. 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. 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.