page_title: Serial port
section_title: Connectors
hierarchical_section_title: Serial port / Hardware / Connectors
caption_attribution_description: English: Serial Port of an ATX PC mainboard.
context_page_description: In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.
  While interfaces such as Ethernet, FireWire, and USB also send data as a serial stream, the term serial port usually denotes hardware compliant with RS-232 or a related standard, such as RS-485 or RS-422.
  Modern consumer PCs have largely replaced serial ports with higher-speed standards, primarily USB. However, serial ports are still frequently used in applications demanding simple, low-speed interfaces, such as industrial automation systems, scientific instruments, point of sale systems and some industrial and consumer products.
  Server computers may use a serial port as a control console for diagnostics, while networking hardware commonly use serial console ports for configuration, diagnostics, and emergency maintenance access.
context_section_description: The only connector specified in the original RS-232 standard was the 25-pin D-subminiature, however, many other connectors have been used, among other reasons to save money or save on physical space. In particular, since many devices do not use all of the 20 signals that are defined by the standard, connectors with fewer pins are often used. 
  The 9-pin DE-9 connector has been used by most IBM-compatible PCs since the Serial/Parallel Adapter option for the PC-AT, where it allowed a serial and parallel port to fit on the same card. This use has been standardized as TIA-574.
  Some miniaturized electronics, particularly graphing calculators and hand-held amateur and two-way radio equipment, have serial ports using a phone connector, usually the smaller 2.5 or 3.5 mm connectors and utilizing the most basic 3-wire interface.
  8P8C connectors are also used in many devices. The EIA/TIA-561 standard defines a pinout using this connector, while the rollover cable (or Yost standard) is commonly used on Unix computers and many network devices, such as equipment from Cisco Systems.
  Many models of Macintosh favor the related RS-422 standard, mostly using circular mini-DIN connectors, except in the earliest models. The Macintosh included a standard set of two ports for connection to a printer and a modem, but some PowerBook laptops had only one combined port to save space.
  10P10C connectors can be found on some devices. Digital Equipment Corporation defined their own DECconnect connection system which is based on the Modified Modular Jack (MMJ) connector. This is a 6-pin modular jack where the key is offset from the center position. As with the Yost standard, DECconnect uses a symmetrical pin layout which enables the direct connection between two DTEs.
  Another common connector is the DH10 header connector common on motherboards and add-in cards which is usually converted via a cable to the more standard 9-pin DE-9 connector (and frequently mounted on a free slot plate or other part of the housing).
  Countless other connectors have been used for RS-232 connections.
caption: PC serial port colored as specified in the PC 97 standard
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