Amstrad made two different disk drives for the Amstrad/Schneider CPC range:
- DDI-1 - a 3" disk drive units including the controller for the CPC464 computer
- FD-1 - a 3" disk drive as secondary disk drive unit for the CPC664, CPC6128 and CPC464 with DDI-1
Technically speaking, the two disk drives were identical, the only difference was that the DDI-1 shipped with controller, manual and CP/M 2.2 on one disk.
The disk drives were jumpered (rather: soldered) to react on both drive selects, A: and B:.
The cable decided which drive became A: and which one became B::
- On the CPC664 and CPC6128 computers, DRIVE SELECT 0 was not wired externally, so the drive could only become drive B: on these systems.
- For the DDI-1, DRIVE SELECT 0 was only wired to the outmost connector of the attached cable, while the inner connector was wired to DRIVE SELECT 1 only, thus the drive at the cable's end always became A: while the other one became drive B: accordingly.
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.