The previous chapters detail the hardware found in the computer case. A great deal of additional hardware can be used by attaching them to the computer using cables. These devices are called peripherals.

In English, the word "peripheral" means something on the edge, or very close outside.

Since peripherals are outside the motherboard and case, they must be connected using a computer peripheral cable.

Cables, Connectors, & Ports

You may heave heard their names, but you may not know what they are: USB, VGA, 1394, Ethernet, and so on. You may have noticed that there are several strange plugs in the sides or back of your computer, and you don't know what they are for. Knowing which cables to use can be important. For example, if you have a laptop, your computer can probably plug in to your TV and use it as an extra monitor.

The Spaghetti Behind Your Desktop

There are several kinds of cables you can use with your computer. Each cable type can be used for different purposes. To use a cable, your computer must have a port (a hole, or socket, which the cable goes into) for that cable. Some computers have many cable ports, other computers only have a basic few. It may be important to know which ports your computer has.

The part of the cable you plug into devices is called a connector (sometimes also a "jack" or a "plug").

Categories of Cables

There are several categories of cables, including:

  • Peripheral cables: used to connect computers to external devices like printers, mice, hard drives, etc.
  • Audio/Video cables: used to connect computers to computer monitors, TVs, microphones and speakers
  • Network cables: used to connect 2 or more computers together in a network

There are a few other categories which we will not focus on. One is "legacy" cables and ports, which refer to old cables and ports which are not used any more. These include serial, PS/2, parallel, and SCSI cables. You do not need to know them, although you may sometimes find them on your computer (especially desktop computers). Some computers still have them so you can continue to use older peripherals.

Peripheral Cables

Peripheral cables are used for many devices, but especially for mice, keyboards, and external storage drives (HDD, DVD, etc.).

Today, the dominant cable type is USB (Universal Serial Bus).

Name Images Versions

[Hi-speed USB (2.0), Superspeed USB (3.0)]

Computer connector:

Peripheral connector:

USB 1.0:

  • Released in 1996
  • Low-speed (12 Mbps), for printers, keyboards, & mice
  • Different shapes for the computer and peripheral connectors

USB 2.0:

  • Released in 2000 (not fully adopted until 2003)
  • Hi-speed (480 Mbps), could be used for almost any peripheral
  • USB most popular
Computer connector:

Peripheral connector:

USB 3.0:

  • Connectors are blue
  • "Ultra" speed (4 Gbps)
  • Slightly different shape for connectors

USB 3.1 — Type C:

  • Uses Type-C connector, similar size to mini/micro connectors
  • Higher "Ultra" speed (10 Gbps)
  • Connectors are reversible

This cable type is gaining popularity. Many new ultrabooks and other mobile devices are so thin that this cable type is usually much better than older versions. The fact that it is reversible (like an Apple Lightning connector) adds to its popularity.

There are a large number of "mini" connectors for USB and other cable types. The more common USB connectors are:

Tech in Your Life

Never Works on the First Try

Isn't this just so true?

There is one way to plug in a USB cable the right way on the first try: look at the connector for a logo. The logo, which is always on a specific side of the connector, usually goes up. However, this does not always help, as some USB ports are sideways. In such a case, if you use the port often, you can try to remember which side it "up."

There is another way, however: a new type of cable becoming available: reversible USB. This allows you to plug in a USB cable correctly on the first try.

The new USB 3.1 Type C connector (pictured previously on the page) is also reversible, but has not yet been widely used.

Audio / Video Cables

You computer can connect to a variety of audio and video devices. Using the audio connectors (usually just a standard audio cable like you use every day), you can attach microphones, speakers, and other audio equipment. The video ports, however, are mostly just for sending video out to a TV or an extra monitor. It is possible to get video into the computer, but usually that requires a peripheral cable.

Here are the standard video and audio cables:

Type Name Connector Port Description
connect to a monitor/ HDTV
HDMI A high-speed video connector used with HDTVs. These are the most popular video cable. Recently, many computers include these. It has built-in DRM copy-protection. Carries audio and video.
DisplayPort Similar to HDMI, it can carry audio and video and has DRM copy protection. However, DisplayPort is cheaper. It is the basis of the new Thunderbolt technology. However, it is not very widely used.
DVI Digital connector, designed for better use with LCD monitors. It is capable of carrying an audio signal, but usually does not.
VGA Most common video monitor cable/port used for computers. Designed for CRTs, but can be used with LCDs. Carries video only.
Audio Audio Used for mono/stereo audio. Most computers use this jack. Famously, Apple did not include it on the iPhone 7.

The transition from old analog "NTSC" TVs to higher-resolution digital HDTVs concluded some time ago. The old S-Video cables will disappear over time as old TV sets are discarded, although use of the Composite/RCA cables continues.

You should become familiar with what cable ports are on your computer. Depending on what ports your computer has, you can connect with a variety of displays and TVs. The ports will also tell you what kind of cables you will need to buy.

Many times, your computer's ports will not match the ports on a cable or TV. Usually, this can be fixed with an adaptor—a cable which has one type of connector at one end, and a different type of connector at the other end. For example, there are cables which have an HDMI port on one end, and a DisplayPort connector on the other, as seen below.

Network Cables

Computers are able to connect together in groups so they can communicate. This is called a "network." When they are connected together in the same location, the network is called a LAN (Local Area Network). The cables used to connect the computers in a network are called Ethernet cables. However, because Ethernet is universal, these cables are also called LAN cables and network cables.

Computers can be also connected in a LAN without wires.

Ethernet cables are very similar to normal telephone cables, except they have 8 wires inside instead of 4. Ethernet cables are also called LAN cables or Network cables. Below are images of Ethernet cables (at left), and telephone cables (at right) for comparison.

Ethernet / LAN / Network Telephone (not LAN)
connector port connector port

Each computer has one Ethernet port. Two computers can be connected directly, with only a cable. Three or more computers require a hub (a device to connect multiple devices) to be used. Using a hub is usually very simple. Just connect the computers to the hub with Ethernet cables; the rest is automatic.

More will be explained about networks in the unit on operating systems.

Other Ports

There are a wide variety of cables, and it would be impossible to review them all quickly. However, here are a few more cable types that you might encounter on your computer:

Thunderbolt Now found mostly on new Macintosh computers, Thunderbolt is a recently-released high-speed peripheral cable. This cable is able to connect to a variety of devices, including video, network, and storage devices; the idea is to consolidate cables into just one, instead of having several different cables connected to the PC. Windows computers still mostly do not include this port.
PC Audio ports

On Windows PCs, especially on the rear panel of desktop machines, audio ports are often color-coded. While some may only have two audio ports (line out / speaker-headphones, and line-in / microphone), some have three to six, and these can be used for home theater sound systems. Very simply, the colors represent:

  • Blue: Stereo Line In; plug in audio-out from CD players and other devices
  • Green: Stereo Line Out; use for speakers or headphones
  • Pink: Microphone
  • Orange: Subwoofer and Center out
  • Black: Rear Surround Speakers for 5.1 and 7.1 home theater systems
  • Gray: Middle Surround Speakers for 7.1 systems (not included if the computer only allows for 5.1 systems)
LEGACY PORTS (ports which are old and often not used any more)
PS/2 PS/2 ports were used for mice and keyboards. This is perhaps the most common legacy port; it can still be found on most desktop computers. It is a very low-speed "serial" connector, which works fine with keyboards and mice, because they do not transmit much data and do not require high-speed connectors. Although any PS/2 device can be used with a PS/2 port, color-coding usually indicated that purple ports are for keyboards, green ports are for mice, and both colors together can be used for either.
Parallel Parallel cables were often used with printers, and may still be on some devices to allow the use of very old printer devices used by some people or companies. It is becoming more uncommon, perhaps due to the fact that its large size takes up too much room on a motherboard.

Standard Peripheral Types

This part of the unit is an informational section. It contains much information already presented in other chapters, but organized in a different way. We will not go over this specific section in class, but you are required to read this and to be familiar with its content.


Virtually every computer has these, although they take various forms.

A computer keyboard is used to input text. There are a variety of types of keyboards, including built-in keyboards for laptops, normal keyboards for desktops, detachable keyboards for tablets, and Bluetooth keyboards for wireless typing.

Ergonomic keyboards are specially designed to better fit the natural shape and position of people's hands, so as to avoid repetitive stress injuries from prolonged typing in uncomfortable positions. "Standard" keyboards are designed poorly for human use.

Unusual keyboard types exist, such as soft plastic roll-up keyboards, laser-projection keyboards, and touchscreen keyboards.

Cursor Control Device (Mouse and Mouse Alternatives)

Typically, people just think of the mouse as the way to move the cursor. However, there are a number of ways to do this.

First, there are a large number of mouse types. The old ball mouse is no longer used in favor of the laser mouse. There are multi-button mice, especially gaming mice. Computer mice also come in ergonomic versions, specially designed to make their use comfortable to the human hand.

Laptop computers typically use trackpads, which are rectangular surfaces located in front of a laptop keyboard. These trackpads are touch-sensitive, usually multitouch (meaning they can detect multiple finger contact points at the same time). These use gestures (special combinations of taps, swipes, and finger movements) to perform specific computer functions. Trackpads can be separate devices, and can be used for desktop computers.

Touchscreens can be used in a similar ways as a trackpad, except with visual responses as feedback. Small touchscreens, including unusual sizes and shapes, can be used on or alongside keyboards. Smartphone or tablets touchscreens can be tasked to act as input devices for computers.

Special mouse devices are sometimes found, such as the trackball, a special mouse device with a large, free-spinning ball on top to move the cursor, or a pointing stick, a small rubber device similar in shape and size to a pencil eraser, which moves the cursor as it is pushed various ways. Special mouth devices are available for people unable to use their hands.

Motion sensors can also be used; a camera or other scanner detects hand movements, and translates them into cursor movements or other control actions.

Cutting-edge research is even making direct brain interfaces possible, where simple thoughts can control the computer.


Any computer will have a screen to relay visual information. Many desktop computers use a separate monitor, but many "All-in-One" models have a built-in screen, as do laptop computers and tablets. Some of these are touch screens, allowing one or more fingers to control the cursor or other computer input functions. Some users prefer multiple monitors to be used for the same computer, sometimes two or three screens used together.

Current computers standardly use flat LCD screens, though larger, heavier, and bulkier CRT monitors were used until just about a decade ago. An alternative to LCD screens is the OLED screen, used in many smartphones and accessory monitors; OLED often provides better control over brightness and contrast for higher-quality display. OLED screens can also be thinner and use less power.

OLED screens tend to be better in almost all respects, but it is currently quite a bit more expensive than LCD. When the price of OLED comes down enough, expect to see much more of them. Many smartphone screens are already using OLED.


Older computers used to use a type of printer called dot matrix, which used metal pins striking paper through an ink ribbon to produce typed printout. Dot matrix printers were extremely noisy and slow, and are rarely used any more.

For higher-quality printing, especially for heavy use, laser printers are preferred. Laser printers use similar technology to copy machines to produce sharp output. Most laser printers are black-and-white, but color laser printers are also available for a higher price. Laser printers use a kind of ink called toner, a fine powder which is applied to paper using heat. Laser printers are best suited for office use, as they are most cost-efficient when hundreds of pages are printed every day.

For home use, inkjet printers are preferred, usually because of the low cost for color printing (though ink prices tend to be high), and because they can be smaller and are easier to maintain. Inkjet printers use liquid ink which is sprayed directly onto the paper in very small amounts, for high-quality output. Inkjets are slower than laser printers, but fast enough for most home and many office applications.

Many printers come in All-in-one designs, including a scanner, printer, and fax machine. In office settings, copy machines are often used as printers, with direct interfaces to computer systems so they can be used just like any printer.

A new type of printer is beginning to appear: the 3-D Printer. These have been around for a while, but mostly were expensive, used for industrial purposes. However, personal 3-D printers are becoming available, most using plastic as the printing material, though printers are available which can print in fabric, wood-based materials, various types of metals, rubber, and other materials—even chocolate! 3-D printers used 3-D models, many available for download from the Internet, as blueprints for a print job. Most printers will "paint" the item one layer at a time, with various resolutions (layer thickness) to provide different levels of quality. Most use an extrusion system, in which the melted material is delivered via a nozzle, but light polymerized types use a light source to solidify materials like plastics, in which objects appear to simply arise from a pool of liquid. Others still use a powder bed, in which a laser is used to solidify powder.


Webcams (a camera, usually in combination with a microphone and speaker) are standard on many computers, especially mobile devices (laptops, tablets, smartphones). They can be built-in, or added separately. They include a small LED light which indicated that the camera is in use. Some include a plastic cover that can be drawn over the camera to provide protection against unwanted observation.

Extra Peripherals

External Drives

All computers have some type of built-in storage, usually a hard disk drive (HDD) or solid state drive (SSD). However, many people have special need for extra storage, temporary storage, or mobile storage. This comes in the form of external drives. They are considered volumes (separate storage devices) by the computer. When connected to a computer, they will be mounted and appear either on the Desktop or in the Computer window as small disk-shaped icons. External drives should be specially ejected before they are removed, in order to prevent possible (but unlikely) damage to the file system.

The most common type of external storage used is in the form of USB Flash Memory Drives. These are small devices which include a USB connector and a platform for flash memory. Current drives range in capacity from 4GB (from around ¥350) to 256GB (around ¥7000). These drives come in a variety of shapes, colors, and sizes. The best are solidly built, and slim so they do not block nearby computer ports. Others can be fun or whimsical designs.

Similar to USB Flash are Flash Memory Cards, simple and flat cards which are inserted into a special slot in a device. There are a variety of card types, most requiring a special reader, but the most popular format is the SD Card. Many computers, printers, tablets, and even phones have built-in SD Card slots for direct access. Small reader devices can also be purchased. Other than their shape and type of connection, they have the same capacities as USB Flash, and work the same way with a computer.

A more powerful external storage solution is the external hard drive (HDD). These hard disk drives have a special casing, and connect via a peripheral cable, usually USB. These provide massive amounts of data storage (usually from 1TB, or 1000GB, up to 4TB) at low cost (lower prices range from ¥6,000 for a 1TB drive to ¥13,000 for a 4TB drive). While some drives use power provided through a USB cable, most require their own separate power source, and need to be plugged in. These drives are extremely useful as back-up for personal computers, or as temporary storage when a computer must be wiped and all software and data re-installed. I would strongly advise any computer user to buy an external drive and use it for backup.

Cloud storage is simply hard disk drives in data farms (special buildings housing massive numbers of data servers with a large number of hard drives) which provide remote storage over the Internet. Local network storage is also possible using a network drive, which is either a drive on one of the connected computers, or is a hard drive with special hardware and software which is connected directly to a local network.

External optical drives (CD, DVD, and Blu-Ray) may also be used, either to listen to or watch media (music and video), or to access data stored on recordable discs.


Scanners take real-world visual information and input that data into computers. There are a variety of types.

The most common type is the flatbed scanner, which is essentially the top part of any copy machine (the glass on which you place a document to be copied), although stand-alone scanners can be purchased as well. Most all-in-one printers also work as document or photo scanners.

A variety of this is the hand-held scanner, which a user slowly runs over a document in order to input it into the computer.

There are also various film scanners which accept film negatives, scan the images, and save them digitally to a computer.

Barcode scanners, including more recent QR Codes, have been long used for a variety of purposes, most famously in supermarkets and shops. Barcodes can contain any information you wish. The LUJ Library uses barcodes for book checkout. Barcodes have traditionally used a laser to scan, but they and QR codes can also be scanned with a camera, usually a smartphone camera, which can accept web page addresses from codes.

Other scanners are used for biometric identification, including fingerprint scanners, and more recently, iris scanners, which read the unique patterns in the irises of your eyes.

Graphics Tablets

These are flat, hard devices of various sizes which accept input from special electronic pens. They are usually designed to read not just contact from the pens, but also read the angle and pressure of the pen input.

Traditionally, the tablets are blank plastic, often with a clear plastic sheet on top under which an image can be placed for tracing. Recently, tablet computers like the iPad Pro use a touchscreen as a graphics tablet, designed to they can ignore parts of the hand touching the screen.

Speakers & Headsets

Any number or manner of speakers can be used easily with computers. The same applies to headphones and headsets (headphones with microphones), both using wires, and wireless (usually Bluetooth) devices.

TVs & Projectors

Using a video port (VGA, DVI, DisplayPort, Thunderbolt, or HDMI), a computer can be connected to a television set or an optical projector, using the external device as a large monitor. these are usually used for presentations and other displays. Most computers can easily be connected to any TV, including the one in your home, and act as an external monitor.

Like extra monitor screens, they can add to the area displayed by the computer, but TV and projector displays are often mirrored, meaning they show exactly what the primary display of the computer is showing.

External Devices

Other devices which are normally independent can be used as computer peripherals. These include smartphones, tablets, digital cameras, video cameras, portable music players, and more. These can be connected with a cable, or wirelessly using Bluetooth, WiFi (network), or Internet connections.

Terms to Know

cablea wire with connectors at either end, used to transfer data from one device to another.
porta hole or socket in a device which can receive a cable connector.
connectoralso "jack" or "plug"; the metal part at one end of a cable which plugs into a port on a device.
peripherala device outside the computer's main chassis.
networkmultiple computers connected together so they can share data.
USBthe most popular peripheral connector, used on virtually every personal computer as well as many other devices.
HDMIa high-speed HD video and audio cable, used especially for televisions and gaming devices.
DisplayPorta high-speed HD video and audio cable, not very common; now part of the newer Thunderbolt technology.
DVIa digital video cable.
VGAan older analog video cable; very standard, it can be found on most video devices.
LANLocal Area Network; a group of computers in a building which are connected together to share data.
Ethernet cablealso called a "LAN cable" or "network cable"; the common cable type used to connect computers in a local network.
huba device which allows multiple devices to connect to each other.
Thunderbolta new, high-speed peripheral cable (found on all new Macintosh computers) capable to connecting multiple peripherals of various types; newer types use fiber-optic connections.
legacy cables/portscables and ports which are outdated and no longer used; some computers offer these ports to allow the use of old equipment.
PS/2a mouse and/or keyboard connector.
ergonomica name for any tool whih is specially designed to better fit the natural shape and position of people's bodies
multitouchsurfaces which are able to detect multiple finger contact points at the same time.
OLEDOrganic Light-Emitting Diode; a type of screen which is an alternative to LCD. OLEDs are thinner, lighter, more flexible, brighter, can be seen from a greater angle, and use less power than LCD screens. Overall, they are much better than LCDs, but they are also more expensive.
All In Onerefers to any design which combines several devices/functions into one unit. Used in printers to refer to a printer/scanner/copier/fax.
3D Printeran emerging technology where one can print 3D (physical) objects via the extrusion or solidifying of plastics or other materials.
SSDSolid State Drive; a type of storage designed to replace hard disk drives. Based on Flash memory, they are faster and smaller than traditional hard drives, but are still more expensive.
Flash Memorya type of non-volatile chip used for data storage. Most commonly seen in USB Flash, Memory Cards, and SSDs
cloud StorageData saved on network computers.
data farma building which contains large numbers of computers with high-volume hard drives, as the basis of services wuch as cloud storage.
biometricmeasurements of human characteristics, such as fingerprints, retina or iris scanners, face recognition, voice recognition, or even scent.

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