Editing Floppy disk drive interface (section)

== Sizes ==

=== 8 inch ===
The de facto standard 8 inch FDD interface is based upon the Shugart Associates models SA800/801<ref name="OEM_SA800"/> FDDs and models SA850/851<ref name="OEM_SA850"/> FDDs.<ref name="Porter_1982"/>{{rp|page=171|quote=SA800, SA801, SA850, SA851, Industry standard for size and interface}} The signal interface uses a 50-pin PCB [[edge connector]] which mates to a flat ribbon cable connector. Separate connectors are provided for both [[Alternate current|AC]] and [[Direct current|DC]] power, as many 8 inch drives used AC spindle motors.<ref name="OEM_SA800"/><ref name="OEM_SA850"/>

=== 5.25 inch ===
[[File:Floppy_buskabel.jpg|thumb|Connectors for 5.25 inch or 3.5 inch FDD (Drive "A") at end of universal two drive FDD cable.  Note '''twist''' in flat cable.]]The de facto standard 5.25 inch FDD interface is based upon the Shugart Associates SA400<ref name="OEM_400"/> FDD.<ref name="Porter_1982"/>{{rp|page=169|quote=SA400, Industry standard for size and interface}} The signal interface uses a 34-pin PCB edge connector which mates to a flat ribbon cable connector. DC power is provided on a separate connector.<ref name="OEM_400"/>  The 34-pin connector is similar in pinout to the standard 50-pin connector for 8 inch FDDs.

=== 3.5 inch ===
The de facto standard for 3.5 inch drives uses a 34-pin [[Pin header|header]] mating to an [[IDC (electrical connector)|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.<ref name="Davis_2015"/> A separate connector is provided for DC power.<ref name="Scott_2006" /> A 'universal' cable would have four drive connectors, two for each size of FDD, although cables which have only two drive connectors are common.  The cable is normally a [[ribbon cable]]. For IBM-compatible floppy controllers, a twist in the cable reverses the order of conductors 10 through 16 for the second connector.  This allows two drives connected to the same cable to be addressed by the host controller without having to select drive assignments with [[Jumper (computing)|jumpers]] on the drives themselves.  Only two drives may be connected to such a cable.  If there are four drive connectors at least two must remain unused.