Computer port (hardware)

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Ports on the Apple iBook (Early 2003)

In computer hardware, a port serves as an interface between the computer and other computers or devices. Physically, a port is a specialized outlet on a piece of equipment to which a plug or cable connects. Electronically, the several conductors making up the outlet provide a signal transfer between devices. Hardware ports may be physically male (unusual, since protruding pins easily break, a fate best left to inexpensive matching cable ends) or female (usual on equipment). Computer ports in common use cover a wide variety of shapes such as round (PS/2, etc.), rectangular (FireWire, etc.), square (telephone modem), trapezoidal (D-Sub—the old printer port was a DB-25), etc. There is some standardization to physical properties and function. For instance, most computers have a keyboard port (currently a round DIN-like outlet referred to as PS/2), into which the keyboard is connected.

Electronically, hardware ports can almost always be divided into two groups based on the signal transfer:

Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-).
Parallel ports send multiple bits at the same time over several sets of wires.

After ports are connected, they typically require "handshaking," which is a similar concept to the negotiation that occurs when two fax machines make a connection, where transfer type, transfer rate, and other necessary information is shared even before data are sent.

Hot-pluggable ports can be connected while equipment is running. About the only port on personal computers that isn't hot-pluggable is the keyboard PS/2 connector; hot-plugging a keyboard on many computer models can cause permanent damage to the motherboard.

Plug-and-play ports are designed so that the connected devices automatically start handshaking as soon as the hot-plugging is done. USB ports and FireWire ports are plug-and-play.

Auto-detect or auto-detection ports are usually plug-and-play, but they offer another type of convenience. An auto-detect port may automatically determine what kind of device has been attached, but it also determines what purpose the port itself should have. For example, some sound cards allow plugging in ("jacking in") several different types of audio speakers, then a dialogue box pops up on the computer screen asking whether the speaker is left, right, front, or rear for surround sound installations. The user's response determines the purpose of the port, which is physically a 1/4" tip-sleeve-ring (TSR) minijack. Some auto-detect ports can even switch between input and output based on context.

At times, special software must be loaded to allow communication (correct signals) for certain devices. This software is called a driver. A driver doesn't change the port, usually, but rather uses the port signal to control the attached device, such as a printer.

Currently (2006) manufacturers have nearly standardized on colors associated with ports on personal computers, although there are no guarantees. The following is a short list:

Orange, purple, or Grey: Keyboard PS/2
Green: Mouse PS/2
Blue or magenta: Parallel Printer DB-25
Amber: Serial DB-25 or DB-9
Pastel pink: Microphone 1/4" stereo (TSR) Minijack
Pastel green: Speaker 1/4" stereo (TSR) Minijack

FireWire ports used with video equipment (among other devices) can be either 4-pin or 6-pin. The two extra conductors in the 6-pin connection carry electrical power. This is why a self-powered device such as a camcorder often connects with a cable that is 4-pins on the camera side and 6-pins on the computer side, the two power conductors simply being ignored. This is also why laptop computers usually only have 4-pin FireWire ports, since they cannot provide enough power to meet requirements for devices needing the power provided by 6-pin connections.

The system bus (or expansion slots) that holds circuit cards for a computer mother board (mobo) has traditionally been a form of parallel port, but current (2006) buses like x1 or x16 are bundled serial ports driven by a part of the mobo called the "north bridge." For example, the x16 is a bundle of 16 connections and thus very fast for video graphics. The physical slot for an x16 is noticeably longer than for an x1. The "south bridge" of the mobo goes out to the more familiar ports, such as USB and parallel printer ports.

Note that optical (light) fiber, microwave, and other technologies (i.e., quantum) have different kinds of connections, since metal wires aren't effective for signal transfers with these technologies. Optical connections are usually a polished glass or plastic interface, possibly with an oil that lessens refraction between the two interface surfaces. Microwaves are conducted through a pipe, which can be seen on a large scale by examining microwave towers with "funnels" on them leading to pipes.

Hardware port trunking (HPT) is a technology that allows multiple hardware ports to be aggregated into a single group, effectively creating a single connection with a higher bandwidth, sometimes referred to as a double-barrel approach. This technology also provides a higher degree of fault tolerance since a failure on one port may just mean a slow-down rather than a dropout. Compare this to Software Port Trunking (SPT) where two agents (websites, channels, etc.) are bonded into one with the same effectiveness, i.e., ISDN B1 (64K) plus B2 (64K) equals data throughput of 128K.