64628f99_nical_Details_and_Instructions__Description
[Signal Name] HD OUT [Description] 
This lets the host machine know if the disk drive is high density or low density, usually a reading of whether an extra hole is physically punched in the disk plastic, or not. People usually put a solid tape over the hole to trick their machines, if they are out of double density stock. However, since the track width is different for high and double density, "taping" can lead to unreliable performance because its hard to erase a 20-wide track with a 10-wide eraser.
USB Floppy Disk Drive Converter/Emulator Technical Details and Instructions
Description