Octopus Overlords

I'm building this rig and using an old floppy cable I had lying around. It doesn't want to connect to the mobo though; it seems as though there is a solid space in one of the pin connectors on the cable, solid plastic, as though there is supposed to be no pin there. But correspondingly there *is* a pin in that location in the motherboard socket.

I think I've got the right end in -- the twisty bit is on the end closer to the floppy drive. I'm wondering if there are any variations on floppy cables, and if it is normal to have that "solid" plastic pin connector on a typical floppy cable. Or if I've got a defective cable or (gasp!) a defective mobo.

Frankly I have little use for a floppy drive anyway, and am proceeding with Windows install regardless. But I would like to know what is going on...

That's a form of 'keying', to make sure you can only put the cable in the way it's supposed to go. One will occasionally see IDE or FD cables with blocked holes, just as you might see connectors with a missing pin.