Datatwin 8 is a peripheral by Pinboard Computers for the Amstrad PCW 8000 series that adds two external 3.5" floppy disk drives.
It features a control switch that allows selecting between internal or external drives as well as their capacity, 180 or 720KB.
A 720KB 3.5" disk is included with CP/M 1.15 and the corresponding drivers to use the external drives.