Changes

Note that the drive also powered the DDI-1 interface when used together with it: Certain pins documented as N/C in the CPC664/CPC6128 manual in fact carry +5V from the drive to the controller.

The main benefit of this was, that you couldn't connect a standard drive with a more common format (5.25" or 3.5") and thus cheaper disks as drive A: without modifications, as the DDI-1 won't work without power.