RetroClinic 1770 Disc Interface

The RetroClinic 177x disc interface (fitted with a VLSI 1772 disc controller chip) fits into the 8271 disc interface socket and upgrades the BBC Micro's disc controller capabilities to allow it to access ADFS formatted floppy discs (with a suitable file system rom) that have an increased capacity of 640Kb and fewer limitations on the number of files and directories able to be stored on the disc media. 

RetroClinic 1770 Disc Interface

The board is supplied in a kit of which there are two versions, one providing Acorn 177x DFS support, the other providing support for the alternative Watford Electronics DDFS system. Both versions of the kit are supplied with ROM's and manuals for the relevant filing system and a suite of logic chips to be fitted to the disc interface circuitry if the BBC Micro to be upgraded does not have an 8271 disc interface fitted already.

You can usually find the kits for sale on ebay or alternatively, you can contact Retroclinic directly to purchase one.