== Technical ==
Dobbertin HD20 is a relative of the Winchester type hard disk and that has an interface that appears to implement the SASI protocol (Shugart Associates System Interface)(a precursor to the SCSI) but which has registers which look similar to those of the OMTI 5510. (The SASI protocol is also used by the SA1000). The controller is a Seagate ST-11M.
There is an expansion port interface which connects to the CPC. It contains a 16KB ROM containing XD-DOS which is normally in slot 6.