Justin A. Parr - Technologist

The Lost Art of the Ribbon Cable

Ribbon cables used to be used for floppy drive, hard drive, and CD / DVD connections.

Ribbon cables were eventually phased out, as floppies are no longer used, and IDE was replaced with SATA.

Early Ribbon Cables

Ribbon cables usually terminate in a pin or edge connector.  Ribbon cables are marked on one edge.

Pin and edge connectors have the individual conductors numbered, starting with pin (or path) #1

Ribbon cables must be connected from pin 1 on the host device (motherboard) to pin 1 on the remote device (peripheral).  In order to identify “pin 1”, ribbon cables are marked along one edge, usually with a black or red stripe.

On the motherboard or peripheral, look for a large dot (white writing on the board), or “PIN 1” or “1” near pin 1.  Install the ribbon cable with the marked edge connecting to pin 1 on both the motherboard and peripheral.

Later Ribbon Cables

Later, ribbon cables had “keyed” connectors that could only be connected in one direction, thus forcing the alignment of pin 1 to pin 1 on the ribbon cable, and pin 1 on the peripheral.

In many situations, one end was keyed, while the other was not.  Knowing how to read a circuit board to find pin 1 would save time, effort, and possible damage to components.

End State

Toward the end of their lifecycle, all connectors were keyed.

Subsequently, the replacement standards, including SATA, USB, and “FireWire” (IEEE 1384) connectors were all keyed.

Initially, SCSI (Small Computer System Interface — “Server” hard drive interface) used a 50-pin ribbon cable, compared to the 40 pin IDE (Integrated Drive Electronics — “standard” PC hard drive) interface.  SCSI cables had up to 15 connectors on one cable, and followed the same “Pin 1” alignment rules.  Later variants of SCSI used keyed connectors.

The modern version of SCSI, called “SAS” (Serial-Attached SCSI), uses SATA style connectors, encapsulating the SCSI protocol within a serial interface.  Like SATA, SAS interfaces are keyed.

Pin 1

Finding “Pin 1” is a lost art, but if you work on older hardware, occasionally, having this skill can be a benefit.