This is the Solidisk Dual Floppy Disc Controller board for the BBC Model B which allows the use of ADFS. The board contains the Western Digital 1770 floppy disc controller which supports MFM density mode as well as FM mode for compatibility with the original DFS.

By the look of it, this board is superior to the upgrade boards produced by Acorn and Watford Electronics because there is provision on board for the 8271 floppy disc controller which the module replaces. This increases compatibility with DFS-format software such as games which sometimes use unofficial calls to the 8271 for protection.

The green lead is either a link to one of the chips on the BBC B motherboard or intended to be attached to a switch to change between 1770 and 8271 modes. I have the fitting instructions somewhere.

The daughter board is going to be put to good use soon in one of my BBC Model Bs. It is about time I had a BBC B with ADFS.