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Most of the periferal device connectors listed below are keyed connectors. A keyed connector has a mechanical feature that prevents it from being connected in the wrong orientation or to the wrong socket, ensuring proper alignment and preventing damage or incorrect connections. This is particularly useful in applications with multiple similar connectors. This is generally achieved via the connector’s shape.

Connectors are listed chronologically.

RS-232

Back in 1960 Recommended Standard 232 was introduced for the transfer of data (and very low voltage power) between a DTE (data terminal equipment) such as a computer terminal or PC, and a DCE (data circuit-terminating equipment or data communication equipment), such as a modem.

The RS-232 standard is commonly used in serial ports and cables where information is transferred one bit at a time. Yes, bit: the smallest possible unit of information (one binary unit). It was developed by the Electronic Industries Alliance.

Ports and cables that implemented the standard include the D-subminiature/Micro-D/D-Sub with popular variants like the 9-pin DE-9 and DB-25 with pins layed out in two rows of four and five for the former and thirteen, twelve for the twenty-five. These cables could actually power a small peripheral device like a mouse and for a long time were utilized for such.

The 1977 Atari Video Computer System game console uses modified DE-9 connectors (male on the system, female on the cable) for its game controller connectors.

The cable ends have a rounded trapezoidal shape like a letter D and include male as well as female variations.

Video Graphics Array (VGA)

The Video Graphics Array (VGA) connector is a 1987 RS-232 variant with fifteen pins that carries analog (no audio) and was for many years prior to DisplayPort, HDMI and DVI the primary video cable and port found on personal computers and video monitors.

The D-shaped connector consists of three rows of five pins (or holes for the receiver) and has screws, typically with plastic handles for physically securing the connection.

Firewire

IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony and Panasonic. It is most commonly known by the name FireWire (Apple), though other brand names exist such as i.LINK (Sony), and Lynx (Texas Instruments). Most consumer electronics manufacturers phased out IEEE 1394 from their product lines in the 2010s.

It was superceded by Thunderbolt, USB 3.0 and SCSI.

Serial Attached SCSI

Serial Attached SCSI (SAS) is a point-to-point serial protocol that moves data to and from computer-storage devices such as hard disk drives, solid-state drives and tape drives. SAS replaces the older Parallel SCSI (Parallel Small Computer System Interface, usually pronounced “scuzzy”).

Universal Serial Bus

Designed in 1986 by Compaq, DEC, IBM, Intel, Microsoft, NEC and Nortel with an open standard, USB superceded ADB, FireWire, game, parallel, PS/2, SCSI, and serial ports.

As of 2024, USB consists of four generations of specifications: USB 1.x, USB 2.0, USB 3.x, and USB4.

There are numerous connector and socket shapes including Standard-A which is a wide rectangle about a half inch by two centimeters and is common on personal computers and USB hubs; Standard-B which is more of a square shape, keyed with a trapezoidal extension at one side and is frequently found in printers and USB compatible musical instruments; Mini-A, Mini-AB and Mini-B which are all smaller, slightly rectangular keyed squares; Micro-A, Micro-AB and Micro-B are also small and more rectangular and finally USB-C (Type-C) which is a small, non-keyed rounded rectangle.

In the Standard types A and B, the slower USB-1 standard is indicated by a black color within the connector and for faster USB-3 the color is blue.

As of this time USB-C has superseded All earlier USB connectors (Type‑A, ‑B, and ‑AB, and their different sizes: Standard, Mini, and Micro), DisplayPort, Mini DisplayPort, Lightning.

Digital Visual Interface

The DVI cable was introduced in 1999, superceding VGA yet maintaining the basic structure of pins (or holes) surrounded by a metal wall with an orientation-defining trapezoidal shape and the hand screws on either side of the plastic casing. It carried video, audio and data (via USB and FireWire).

Unlike VGA these connections supported hot-swapping, meaning that components could be added to a system without requiring a restart to activate. Since the analog pins are directly compatible with VGA signaling, passive adapters are simple and cheap to produce, providing a cost-effective solution to support VGA on DVI.

Of the five DVI variations one (DVI-A) supported analog data, two (DVI-D) digital and two (DVI-I) both digital and analog. The digital and integrated cables each came in single and dual link variants, and each of the variants had a different pin configuration, which was one of the compatibility limitations of the standard.

Hi-Definition Media Interface

Designed in 2002 by HDMI Forum (Founders: Hitachi, Matsushita, Maxell, Philips, Silicon Image, Sony, Thomson and Toshiba) and superceding both the DVI and VGA as well as SCART, S-Video, and RCA connector, HDMI is commonly used to connect devices such as televisions, computer monitors, projectors, gaming consoles, and personal computers. HDMI supports uncompressed video and digital audio either compressed or uncompressed, allowing a single cable to carry all audiovisual signals.

It superceded SCART, S-Video, DVI, VGA and RCA connector.

The connection itself is keyed as a horizontal rectangle expanded at the top to include a trapezoid-smaller at the top-and comes in four variations: A, C, D and E (standard, mini, micro and automotive respectively).

DisplayPort

Designed in 1989 by VESA, formally known as Video Electronics Standards Association, to replace older standards like VGA, DVI, and FPD-Link, DisplayPort uses a self-clocking, micro-packet-based protocol that allows for a variable number of differential pair lanes as well as flexible allocation of bandwidth between audio and video, and allows encapsulating multi-channel compressed audio formats in the audio stream. DisplayPort 1.2 supports multiple audio/video streams, variable refresh rate (FreeSync), and Dual-mode transmitters compatible with HDMI 1.2 or 1.4.

DisplayPort connectors are recognizable by their asymmetrical keying.

Unlike older interfaces, DisplayPort uses packet-based transmission, similar to how data is sent over USB or Ethernet. The design enables support for high resolutions and adding new features without changing the connector.

DisplayPort includes an auxiliary data channel used for device control and automatic configuration between source and display devices. It supports standards such as Display Data Channel (DDC), Extended Display Identification Data (EDID), Monitor Control Command Set (MCCS), and VESA Display Power Management Signaling (DPMS). Some implementations also support Consumer Electronics Control (CEC), which allows devices to send commands to each other and be operated using a single remote control.