Floppy disk drive interface

[1] For example, before adopting 3.5-inch FDD standards for interface, media and form factor there were drives and media proposed by Hitachi, Tabor, Sony, Tandon, Shugart and Canon.

[2] The de facto standard 8 inch FDD interface is based upon the Shugart Associates models SA800/801[3] FDDs and models SA850/851[4] FDDs.

The de facto standard for 3.5 inch drives uses a 34-pin header mating to an IDC Berg connector, collectively slightly smaller than the PCB edge pin connector and mating socket used for the 5¼ inch standard but with the same 34 pin definitions as the 5¼ inch standard.

For IBM-compatible floppy controllers, a twist in the cable reverses the order of conductors 10 through 16 for the second connector.

When introducing the PC, IBM sliced the cable between the first and second drive, and twisted seven of the conductors, effectively flipping the four conductors which specifically addressed the first or second drive.

As the IBM PC created a market for clones and compatibles, many manufacturers adopted the same cable twist system, although jumpers may still be required on systems that are older, or not based on the IBM PC.

[9] The drive that is at furthest end of the cable additionally would have a terminating resistor installed to maintain signal quality.