Amstrad External Disk Drive

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Amstrad made two different disk drives for the Amstrad/Schneider CPC range:

  • DDI-1: a set consisting of the real DDI-1 (= Disk Drive Interface) and a FD-1 3" disk drive, as well as the CP/M 2.2 license and disk.
    This set was for the CPC464 which didn't have a built-in 765 FDC disk controller.
  • FD-1: a 3" disk drive as secondary disk drive unit for the CPC664, CPC6128, and for the CPC464 with DDI-1

All drives are for use with CF2 Compact Floppy Disc 3" discs.

There was no official external disk drive for the 6128Plus or even the 464Plus. The difference between a CPC664/CPC6128 and a 6128Plus was simply a changed pin-out which can easily be solved by a new plug on the disk drive's cable.

The 464Plus was harder to equip with a disk drive. Although the pin-out of the expansion port was left unchanged, the DDI-1 cannot be used on the 464Plus without modifications (see Connecting a Disc Interface to CPC464+).

Technical Details

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 (more accurately, soldered) to react on both drive select lines, 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 connected on the external connector, so the drive could only become drive B: on these systems.
  • For the DDI-1, DRIVE SELECT 0 was only wired to the outermost 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 reason for this was that you couldn't connect a standard drive with a more common format (5¼" in the beginning, 3½" later and today) and thus cheaper disks as drive A: without modifications, as the DDI-1 wouldn't work without the power fed from the FD-1.

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