John Cletheroe's
PC and Internet Hints

Computer Connections, Interfaces, Ports, Plugs And Sockets, Etc

Introduction

IMPORTANT: To avoid any risk of damage to equipment, always switch off and disconnect the mains from all devices before connecting or disconnecting any signal cables other than USB.

This page describes the connections found on domestic PC's. It does not describe business computers, servers, etc. Telephone connections mainly relate to the UK and other countries differ.

This page describes the connections on the computer. The connections on cables that connect to the computer will be of the opposite gender. The physical design of the connections at the peripheral, phone socket, etc, may be the same as on the computer or may differ.

10 base 2

See "Thin Ethernet".

2.1

When describing speakers, two normal speakers (left and right) and one sub-woofer (bass speaker).

3G

A mobile phone system standard, capable of carrying the HSDPA or the HSUPA protocol for mobile broadband connections. Presumably the name 3G implies "third generation".

5.1

When describing speakers, two normal speakers (left and right), three extra speakers (rear left, rear centre and rear right, I think), and one sub-woofer (bass speaker).

802.11a, 802.11b, 802.11g, 802.11n, etc

Standards for local wireless network connections between a computer and a wireless router. The later the letter in the alphabet, the more modern the version is, and therefore in theory faster. In practice the speed of the connection between the wireless router and the server will be much lower, making the speed of the local wireless network connection largely irrelevant.

ADSL

Asynchronous Digital Subscriber Line, the official name for the most common form of broadband Internet connection over a conventional phone line in Britain. See "Broadband".

ADSL Filter

Also called a broadband filter.

In Britain (and probably other countries an ADSL filter must be used with every device plugged in to an ADSL-enabled phone line. This includes not only the modem or router, but also every phone, answerphone machine and satellite television set-top box.

An ADSL filter has a BS6312 plug which plugs into the phone line, a BS6312 socket into which a normal telephone can be plugged, and an RJ11 socket into which an ADSL modem or router can be plugged. The filter passes the small range of human voice frequencies to and from the telephone, and the much greater range of higher frequencies to and from the modem or router.

Aerial

See "Television Aerial".

AGP

Accelerated Graphics Port or Advanced Graphics Port. A nearly obsolete interface standard for connecting a video board (graphics card) to the system board inside the computer. An edge connector socket is mounted on the system board, into which the edge of the video board is plugged.

PCI-E has now very nearly replaced the AGP video board interface standard. AGP and PCI-E are not compatible with each other.

There have been various versions of AGP and it is vital to check both the physical and electrical compatibility when purchasing a video board.

AT Attachment

See "IDE".

ATA

See "IDE".

Audio

See "Sound".

AV (Audio-Video)

See "Phono".

Baseband

In electronics generally, "baseband" refers to the transmission of a signal at its normal frequency, unmodulated. With analogue signals a baseband system will give better quality than a modulated RF (radio frequency) system and is therefore the preferable option. For example, a SCART connection between a VCR and a television operating at baseband will give a much better picture quality than an aerial connection which involves modulation to a UHF channel in the VCR and then demodulation in the television.

In the area of Internet connections, the term means the use of a dial-up telephone connection with the data being sent as tones within the frequency range used for normal voice calls, and therefore at a very much slower speed than with broadband. Therefore with computers baseband is the less desirable option.

BNC

A type of coax connector with a twist lock. BNC connectors were widely used for 10 base 2 thin Ethernet but this appears to no longer be the case. The name comes from "Bayonet Neill Concelman".

Bluetooth

A wireless networking standard, used I believe for connecting wireless keyboards and mice to their computers. Bluetooth and wi-fi are two different systems.

Broadband

The transmission of computer data over a wider range of frequencies than that used for normal voice telephone calls, with a subsequent substantial increase in speed.

A broadband Internet connection can take various forms, for example:

In each case the modem or router must be connected to a phone line or cable television system.

Broadband Filter

See "ADSL Filter".

BS6312

The British standard for normal domestic telephone equipment plugs and sockets. All normal British telephones have cables terminating with a BS6312 plug. The plug clips into the socket. A plastic clip must be pressed in order to remove the plug from the socket. Plugs are normally made with opaque plastic. There is space in the connectors for up to six conductors but in most cases not all the spaces are used.

BS6312 plugs and sockets are not the same as RJ11 or RJ45.

British ADSL broadband subscriber connections use RJ11 plugs and sockets.

Other countries use other designs of plugs and sockets for domestic telephone equipment.

Cable Modem

A modem for use with a cable television system (I think).

Card Reader

I'm sorry, this is not a topic on which I can offer any information.

CD Drive

See "External Optical (CD Or DVD) Disk Drive".

Cassette Recorder

Historical. The very first IBM PC model had a full-size DIN socket with which a cassette recorder could be connected. This was used as a storage medium for programs and data files, in the same way as with other early personal computers such as those manufactured by Commodore, Sinclair, etc. Modern computers do not have this type of connection.

Coax

Coaxial cable, in other words cable with an internal signal cable surrounded by a grounded braid which protects the signal from interference. Coax cable is used for to carry very low voltage signals which are especially subject to interference such as those from television aerials and satellite dishes. Coax cables have an inherent capacitance and it is important that the device to which they are attached matches this. See also "Television Aerial".

Centronics

See "Parallel Printer".

COM1:, COM2:

See "Serial Port".

Comm Port

See "Serial Port".

Component Video

The transmission of video (television pictures) as separate components (for example, red green and blue, or luminance chrominance and hue) rather than as a single composite signal. Component video usually results in a significantly better picture quality than composite. Component video is sometimes called RGB video (for red, green and blue).

Composite Video

The transmission of video as a single combined signal. Composite video usually gives a far inferior picture quality to component video.

Connection

Windows uses the word "connection" in a potentially very confusing way. Instead of referring to a physical connection, in Windows a "connection" is a set of network, wireless network, or Internet configuration settings. It is quite possible for more than one Windows "connections" to all use the same physical connection from a computer via a modem or router to the Internet, for example if more than one ISP account is used from the same computer. Windows does not use this terminology when referring to the configuration settings of any other physical interfaces or ports.

Dial-Up

A connection via the conventional public switched telephone system, i.e. not broadband/ADSL. A normal phone number (probably an 0845 or 0800 number) must be specified when a dial-up connection is created in Windows.

DIN

Deutsches Institut fur Normung (German Institute for Standardization). Full size DIN plugs and sockets were used on some audio devices such as early Philips cassette recorders. IBM used them for the keyboard and cassette recorder connections on the first model of the IBM PC. Mini-DIN connectors were first used for the keyboard and mouse on the IBM PS/2 and are still often referred to as PS/2 connectors to this day.

Dongle

The word "dongle" has two common meanings:

DVD Drive

See "External Optical (CD Or DVD) Disk Drive".

DVI

Digital Visual Interface. One of the two modern standards for connecting the output from a video board to a monitor (the other being VGA). Most modern equipment has both DVI and VGA connections but only one of these should be connected, never both at the same time.

DVI plugs and sockets are coloured white. There are various possible arrangements of the pins, of which there are normally a large number.

Ethernet

Also often called "Network", as all other types of local area network such as token ring have now virtually died out.

Ethernet connectors on computers are RJ45 sockets. The following symbol is often found next to an Ethernet socket: a straight line with three very short straight lines coming off it at ninety degrees, each with a very small square at the end. Sometimes the very short lines are omitted.

Ethernet can be used to connect two or more computers and other devices (such as printers) within the same building, or more commonly now to connect a computer to a router. Wireless routers often need to be connected to a computer with a cabled Ethernet connection while they are being configured. After configuration the connection can be cabled or wireless as desired.

External Hard Disk

An external hard disk can be connected to a computer by various means, including:

External Optical (CD Or DVD) Disk Drive

An external optical disk drive is normally connected to a computer by USB but there may be other possibilities such as Ethernet or a wireless network connection.

Firewire

A system similar in concept to USB. Also called IEEE 1394 and i.Link. I'm sorry, I can't offer any more information on this topic.

Games Port

Also called a joystick port.

Historical. As far as I know, joysticks for modern PC's are always connected via USB.

Very early IBM PC's had a D connector into which a simple joystick could be connected. Only on/off switches could be sensed, for the four directions of up, down, left and right, plus a "fire" button.

I am not familiar with how games controllers are connected to modern games consoles.

Graphics Adaptor (Video Board)

See "AGP" and "PCI-E".

Hard Disk

See "External Hard Disk".

HDMI

High-Definition Multimedia Interface. A digital video connection system.

Headphones

Headphones can be connected to the green line-out mini-jack socket.

I.Link

See "Firewire".

IDE

Integrated Drive Electronics. Also sometimes called AT Attachment or ATA.

IDE is an internal connection, inside the computer's case, used to connect hard disks and optical (CD or DVD) drives to the system board. There are normally two IDE ports on the system board, into each of which a ribbon cable is connected. The ribbon cable has two further connectors which can be plugged into hard disks and optical drives.

With IDE, pin 1 on the system board must be connected to pin 1 on each device, and one wire of the ribbon cable is coloured red to assist in this. Each device must be designated by means of tiny jumpers located near the ribbon cable connector as a master, or slave, or "cable select" (which means that the connections on the ribbon cable will set it as a master or slave). Each ribbon cable can take one master device and one slave device. There are also considerations for optimising the combination of devices on each ribbon cable.

IDE is largely being superseded by SATA.

IEEE

"Eye triple e". Institute of Electrical and Electronics Engineers. A standards organisation based in the USA.

IEEE 1394

See "Firewire".

Internet

A computer can be connected to the Internet in a variety of ways, including:

ISA

Industry Standard Architecture. One of several possible mutually incompatible interface standards for connecting adaptor boards to the system board inside the computer. Edge connectors are mounted on the system board, into which the edges of the adaptor printed circuit boards are plugged.

Other possible interfaces for adaptor boards include PCI.

ISDN

Integrated Services Digital Network. Historical. An Internet connection system over conventional phone lines which offered slightly higher speeds than with dial-up modems. Now superseded by ADSL which delivers much higher speeds.

Joystick

See "Games Port."

Keyboard

A keyboard can be connected to a PC in various ways, including:

Line-In

A blue mini-jack socket. This is for connecting the low level output from an audio device such as a cassette player or an audio mixer. It is not for connecting the speaker output from such a device. Nor is it for connecting a microphone.

Line-Out

Also sometimes called speaker output.

A green stereo mini-jack socket. This is a low-power output, for connection to powered speakers or headphones, or an audio amplifier, cassette recorder, mixer, etc. It is not suitable for direct connection to full size unpowered speakers.

Mains

Desktop computers usually have a "kettle lead" connector into which the mains power cable is connected. There may be a voltage adjustment slider nearby for setting to UK/European or USA mains voltage.

Portable (laptop) computers usually have an external power supply, with a cable ending in a concentric plug to connect the low voltage DC power to the computer.

Mic, Microphone

A pink mini-jack socket. Only suitable for connecting a microphone. Not suitable for connecting the line-out or speaker output from audio devices, televisions, etc.

MIDI

Musical Instruments Digital Interface. A system for sending commands between keyboards and other similar devices. The commands play musical notes. As far as I know no modern equipment uses the MIDI connection system, but the name lives on in the MIDI file format which was a popular method of recording and transferring instrumental music before greater storage capacities, fast connections and the adoption of MP3 made it viable to handle actual recordings.

Mini DIN

See "PS/2".

Mini USB

Small USB-B plugs and sockets, often used on devices such as digital cameras.

Mobile Broadband

A broadband Internet connection between a computer and an ISP (Internet Service Provider) via a mobile phone network, usually using the HSDPA or HSUPA protocol. A suitable modem (often called a "dongle") is used and this device plugs into a USB port on the computer.

Mobile broadband is not the same as wireless networking, wireless LAN, WLAN, or wi-fi.

Modem

A modem (modulator/demodulator) is a device which allows a computer to be connected to a phone line (dial-up or broadband/ADSL), cable television system, or mobile phone system. A different type of device is needed in each case.

A modem can be internal (either mounted on the system board or in the form of an adaptor board) or external.

An internal modem will have a socket accessible on the outside of the computer, into which a cable can be plugged to connect to the phone line.

An external modem can be connected to a computer in various ways, listed under "Internet".

Conventional dial-up phone line modems, both internal and external, may have an additional socket into which a normal phone can be connected. The socket marked "line" should be connected to the phone line, and the socket marked "phone" is for the optional additional normal phone. If there are only meaningless symbols labelling the sockets, some experimentation may be required.

A broadband Internet connection can be implemented using a router or a broadband modem.

Monitor

There are currently two common methods of connecting a monitor to a computer, DVI and VGA (see those topics for more information).

Most modern computer video boards and monitors have both of these options as standard. Only one of the two should be connected, never both at the same time.

Mouse

A mouse can be connected to a computer in various ways, including:

Network

In modern domestic PC's, this term usually means "Ethernet", as all other types of local area networking such as token ring have now virtually died out.

NIC

Network Interface Card, i.e. an Ethernet adaptor. The term is also sometimes used for the network (i.e. Ethernet) connection on a computer, which is an RJ45 socket.

Optical (CD Or DVD) Disk Drive

See "External Optical (CD Or DVD) Disk Drive".

Parallel Printer Port, or Parallel Port

Also called a Centronics port. I believe that name comes from the manufacturer of the physical connectors at the printer end of the cable.

The parallel printer connector on a computer is a 25-way D plug. On modern computers the connector, or the area of the case in which it is mounted, may be coloured red or maroon. On modern computers the parallel printer port may be designated by a symbol of a rectangle (representing a printer) with a sheet of paper coming out of it.

The parallel port can only be used to connect a suitable printer. Nearly all modern printers have USB interfaces, which are not compatible, making the parallel port nearly obsolete.

PCI

Peripheral Component Interconnect. One of several possible mutually incompatible interfaces for connecting adaptor boards to the system board inside the computer. Edge connectors are mounted on the system board, into which the edges of the adaptor printed circuit boards are plugged.

Other possible interfaces for adaptor boards include ISA.

PCI-E is a different system board interface standard, being solely for video boards (graphics cards).

PCI-E

The modern standard for connecting a video board (graphics card) to the system board inside the computer. An edge connector socket is mounted on the system board, into which the edge of the video board is plugged.

There have been various versions of PCI-E and it is vital to check the physical and electrical compatibility of the sockets when purchasing a video board.

PCI and PCI-E are very different. PCI is not specifically for video boards.

PCI-E has now very nearly replaced the AGP video board interface standard. AGP and PCI-E are not compatible with each other.

PCMCIA

Personal Computer Memory Card International Association. A type of connector used on portable computers (laptops), into which small peripheral cards can be plugged.

Phone

A computer can be connected to a phone line by means of a modem or a router. See those entries for more information.

Phono

Also called AV (audio-video) or RCA (from Radio Corporation Of America).

Each phono connector has two conductors, an inner signal wire and an outer grounded shield to protect against interference.

The phono connection system is widely used to connect audio devices such as cassette players, audio CD players, audio amplifiers, etc. Usage of phono connections for video connections is mainly restricted to the USA. For audio connections there are usually separate phono connectors and cables for each of the two stereo signals (left and right). For video connections there can be separate phono sockets and cables for each video component (red green and blue, or luminance chrominance and hue), or a single "composite" cable. Composite video usually gives a very inferior picture quality.

Phono connectors are sometimes colour coded.

Power

See "mains". In addition to the mains power socket (or DC power socket for a portable computer), there are power supply connections within the computer to the system board, hard disks, optical (CD or DVD) drives, fans, etc. Modern powerful video boards also generally require a power supply connection as they cannot obtain sufficient current via their PCB edge connectors.

Printer

A printer can be connected to a computer by various means, including:

PS/2

The name given to a type of mini-DIN socket, often used for connecting keyboards and mice to computers prior to USB becoming so widespread. The name comes from the first use of this type of socket on the IBM PS/2 computer.

The purple PS/2 socket is for the keyboard and the green PS/2 socket is for the mouse.

In another context, PS2 also refers to the Sony Playstation 2 video game console.

RCA

See "Phono".

RGB Video

See "Component Video".

RJ11

A standard type of connector used in Britain for domestic ADSL broadband connections. ADSL filters have RJ11 sockets for connections to ADSL modems and routers, which in turn have cables terminating in RJ11 plugs.

RJ11 plugs are usually made of transparent plastic and click into position. To remove the plug, a small plastic clip must be pressed.

An RJ11 connector has space for up to six conductors in six parallel channels but some spaces may not be used.

RJ11 plugs and sockets may be used in other countries for other purposes. For example, I believe RJ11 connectors are used for normal telephones in the USA.

It would appear that the connectors to the telephone line on dial-up modems, both internal and external, are RJ11 sockets. The same seems to also be true of broadband modems and routers. However, I have not researched this extensively.

British domestic normal phone connections are BS6312 plugs and sockets, which are different to RJ11.

RJ45

A standard design of connector used on Ethernet network interface cards. Ethernet connections on modern personal computers, modems and routers are RJ45 sockets. Ethernet cables terminate with RJ45 plugs. RJ45 plugs are usually made of transparent plastic and click into position. To remove the plug, a small plastic clip must be pressed.

An RJ45 connector has space for up to eight conductors in eight parallel channels but some spaces may not be used.

BS6312, RJ11 and RJ45 are all different to each other. I believe it may be physically possible to insert an RJ11 plug into an RJ45 socket but the consequences of doing so may be dire.

RS-232

See "Serial Port".

S-Video

A video (television picture) connection system which is a compromise between composite and full component video. Some computer video boards have S-Video outputs, which in some cases can be connected to a normal television. I advise checking extensively before doing so, however.

SATA

Serial ATA. Currently the most commonly used method of connecting internal hard disks to system boards, inside the computer. SATA has largely replaced IDE.

SCART

Syndicat des Constructeurs d'Appareils Radiorecepteurs et Televiseurs. The universal method of connecting standard definition television equipment (such as television sets and VCR's) in Europe, including Britain. Rarely if ever used with computers, except when converter cables are used with a SCART plug on one end for the television and a suitable different connector on the other end for the computer.

(As an aside, many man-centuries of exceedingly painful effort have been expended in viewers' attempts to find a combination of SCART cable connections which allows one television programme to be watched while a different programme is being recorded.)

Screen

See "Monitor".

SCSI

Small Computer System Interface. Historical (as far as I know).

SD Memory Card

Some portable (laptop) computers have sockets into which SD and possibly some other types of memory card can be inserted. I believe card reader units are available to perform the same function with desktop computers.

Serial Port

Also called COM1:, COM2:, Comm Port, or RS-232. COM1: and COM2: are the device names used in DOS to refer to the first two serial ports.

A serial port on a computer is a 9-way D plug. On modern computers the connector, or the area of the case in which it is mounted, may be coloured green. In addition, the port may be indicated by a symbol of noughts and ones (although I'm not sure whether that symbol can also be used for some other connections).

Most modern computers have one serial port. In theory a computer can have up to four serial ports but nowadays this is extremely rare. Even in the past, more than two serial ports was very uncommon.

Currently the use of a serial port is mainly restricted to the connection of a dial-up modem, but in the past serial ports had a variety of other possible uses, including the connection of:

Sound

The sound input and output connections on a computer are normally mini-jack sockets, colour coded as follows:

Speakers

Powered speakers, or an audio amplifier driving unpowered speakers, can be connected to the line-out mini-jack socket which is coloured green.

Sub-Woofer

A low-frequency bass speaker, used to enhance the bass sounds. A sub-woofer is connected to the yellow sound mini-jack socket.

Television Aerial

A television aerial connection to a computer is only relevant if the computer has a television tuner card. Different types of connectors and/or cables are used for British conventional television aerials, US conventional television aerials, and satellite dishes. I do not know which of these types, if any, are used for television tuner cards fitted in computers.

Thin Ethernet

Also called 10Base2 (from 10 Mbits/second, baseband, maximum segment length 200 yards). This local network design is now historical. It used BNC connectors.

Token Ring

A type of local network design, now historical.

USB

Universal Serial Bus. An extremely common method of connecting external peripherals to a computer.

At the computer end a rectangular USB-A connector is used. At the peripheral end a nearly square USB-B connector is used. On small devices such as digital cameras a mini USB-B connector is used. Some very small USB devices such a memory sticks and wireless network adaptors plug directly into the computer with no need for a cable.

The following symbol is used to denote a USB connector: a straight line with a dot at one end and an arrow at the other, with two short curved lines branching off it, each leading to dots.

Devices which can be connected via USB include:

It is not electrically safe to connect two computers with USB, hence the different type of connectors at the computer end and the peripheral device end to prevent this being done accidentally.

Some devices which use very little power, such a USB memory sticks and USB wireless network adaptors, derive their power through the USB connection. Devices such as optical (CD and DVD) drives usually require their own power supply. External hard disks with USB interfaces may or may not require their own power supply.

It is possible to effectively increase the number of USB connections by use of a USB hub. One USB socket on the computer is used to connect the hub, which has a number of USB sockets into which devices can be connected.

For a small number of devices which use very little power, or which have their own mains supply, an unpowered USB hub may be sufficient. However, a powered USB HUB will generally be more reliable and allow more devices to be connected.

There have been several versions of USB, with later versions offering considerably faster speeds. Most devices tend to be compatible across different versions, operating at the speed of the slower device. However, one old USB version device plugged in to a USB "tree" may slow down the whole tree.

Unlike nearly all other computer connections, it is electrically safe to connect and disconnect USB cables with the power on. However, with devices such as external disk drives it is vital to use the "Safely Remove Hardware" icon on the System Tray before disconnecting, so as to ensure that all data has been written to the disk.

VGA

Video Graphics Array. One of the two modern standards for connecting the output from a video board to a monitor (the other being DVI). Most modern equipment has both DVI and VGA connections but only one of these should be connected, never both at the same time.

VGA connectors on video boards are 15-way D sockets. Modern VGA connectors are coloured blue.

Video Board (Graphics Adaptor)

See "AGP" and "PCI-E".

Video Output

Some video boards have outputs such as S-Video which can be connected to televisions. Check the video board and television documentation carefully before making such a connection, and then only with both devices switched off.

Wi-Fi

See "Wireless Network".

Wireless LAN

See "Wireless Network".

Wireless Network

Also called Wi-Fi, Wireless LAN and WLAN.

With desktop computers a wireless network adaptor is required. These devices usually have USB connections and are very similar in appearance to USB memory sticks.

Modern portable computers (laptops) tend to have a wireless network adaptor built-in as standard.

See also "Bluetooth" which is a wireless connection system for keyboards and mice.

Wireless Router

A device which has a wired connection to a conventional phone line or cable television system, and wireless connections to computers and possibly other devices such as printer in the same building. Unlike a modem, with a router more than one computer can be connected to the Internet at the same time, and in addition information can be passed between the computers.

Wireless routers often need to be connected to a computer with a cabled Ethernet connection while they are being configured. After configuration the connection can be cabled or wireless as desired. See also "Ethernet".

WLAN

See "Wireless Network".

Woofer

See "Sub-woofer".
PC and Internet Hints

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As with all the other pages in this area, all the information on this page is solely the opinion of the author, who has no connection whatsoever with any of the companies and organisations mentioned.
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Most recently modified 18-Oct-08