Allows to upgrade a single -S drive to a dual -D drive.
=== FD1 FD-1 drive adapter ===
Since the The Vortex F1-D was /M1 drives were originally intended as an upgrade upgrades to CPC 464 setups already having a DDI-1, this /FD-1. This adapter allowed to continue using the 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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