This is also a double density format with catalogues similar to Acorn DFS.

It uses 19 bit file lengths and 11 bit LBAs throughout, but the 'extra' bits are stored in the top bits of the disc title and file names, which are cleared in Acorn DFS.

Sources

This section is based loosely on the following:

• Acorn DFS disk format - beebwiki.mdfs.net
• Acorn, Watford, Solidisk and Duggan DFS Filesystem Structure mdfs.net