Allows to upgrade a single -S drive to a dual -D drive.
=== 3" FD1 drive adapter ===
Since the F1-D was originally intended as an upgrade to CPC 464 setups already having a DDI-1, this adapter allowed to continue using the FD-1 3" FD1 floppy drive. Since only two drives can be used simultaneously, the drive had to be selected manually using a RSX command.
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