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COMPUTER INPUT/OUPUT DEVICES

Class: Comp. Sc A/L By: DZEUGANG PLACIDE

The computer system essentially consists of three components: input devices, central

processing unit and output devices. In the computer terminology, a device can be referred as

a unit of hardware, which is capable of providing input to the computer or receiving output or

both. The input devices are used to provide data to the central processing unit (CPU) for

processing. After processing, the input data are converted into meaningful information and

this output is presented to the user with the help of output devices. When the term 'device' is

used, it includes keyboard, mouse, display monitors, printers and other hardware units.

The aim of this chapter is to familiarize you with various types of output and output devices

along with their advantages, disadvantages and applications.

Table of Contents

I. INPUT DEVICES ........................................................................................................................... 2

I.1 Keyboard ....................................................................................................................................... 2

I.2 Pointing Devices ............................................................................................................................ 2

I.3 Speech Recognition System .......................................................................................................... 3

I.4 Digital Camera ............................................................................................................................... 4

I.5 Webcam ......................................................................................................................................... 4

I.6 Scanners ......................................................................................................................................... 4

I.7 Bar Code Reader ............................................................................................................................ 4

I.8 Optical mark recognition ............................................................................................................... 5

I.9 Optical Character Recognition ...................................................................................................... 5

I.10 Magnetic-Ink Character Recognition .......................................................................................... 5

II. OUTPUT DEVICES ....................................................................................................................... 5

II.1 Types of Output ............................................................................................................................ 6

II.2 Printers ......................................................................................................................................... 6

II.3 Plotters .......................................................................................................................................... 8

II.4 Computer Output Microfilm ........................................................................................................ 8

II.5 Monitor ......................................................................................................................................... 9

II.6. Projectors ................................................................................................................................... 10

II.7 Electronic Whiteboard ................................................................................................................ 11

II.8 Headphones and Headsets .......................................................................................................... 11

II.9 Terminals .................................................................................................................................... 12

Ministry of Secondary Education

Progressive Comprehensive High School

PCHS Mankon – Bamenda

Department of Computer Studies

Republic of Cameroon

Peace – Work – Fatherland

School Year 2013/2014

Topic: Input/output devices Par DZEUGANG PLACIDE


I. INPUT DEVICES

An input device can be defined as an electromechanical device that allows the user to feed

data into the computer for analysis and storage, and to give commands to the computer. The

computer accepts input in two ways; manually and directly. In the case of manual data entry,

the user enters the data into the computer by hand, for example, by using the keyboard and

the mouse. A user can also enter the data directly by transferring information automatically

from a source document (like from check using MICR) into the computer.

Some of the commonly used input devices are keyboard, pointing devices like mouse and

joystick, speech recognition system, digital camera, scanners and so on.

I.1 Keyboard

A keyboard is the most common data entry device. The keyboard is designed like a regular

typewriter with a few additional keys. The data are entered into the computer by using

various keys. There are different types of keyboard layouts such as QWERTY, DVORAK

and AZERTY, but the most common layout is the QWERTY.

Working of a Keyboard

At its essence, a keyboard consists of a series of

switches connected to a small keyboard

microprocessor that monitors the state of each

switch and initiates a specific response to a

change in that state. When the user presses a key,

it causes a change in the amount of current

flowing through the circuit associated specifically

with that key. The keyboard microprocessor

detects this change in the current flow.

I.2 Pointing Devices

A pointing device is used to communicate with the computer by pointing to the locations on

the monitor. Such devices do not require keying of characters, instead the user can move a

cursor on the screen and perform move, click or drag operations. Some of the commonly used

pointing devices are mouse, trackball, joystick, light pen, touch screen and trackpad.

I.2.1 Mouse

A mouse is a small rectangular-shaped hand-held pointing device, It usually contains two or

three buttons, which can be used to input commands or the data.The mouse may be classified

as a mechanical mouse or an optical mouse, based on the technology it uses.

→ A mechanical mouse uses a rubber ball at the bottom surface, which rotates as the

mouse is moved along a flat surface to move the cursor.

→ An optical mouse uses a light beam instead of a rotating ball to detect the movement

across a specially patterned mouse pad.



I.2.2 Trackball

A trackball is another pointing device that resembles a ball nestled

in a square cradle and serves as an alternative to a mouse. In general,

the trackball is like a mouse turned upside down. It has a ball, which

can be rotated by fingers in any direction, and the cursor moves

accordingly.

I.2.3 Joystick

A joystick is a device that moves in all directions and controls the

movement of the cursor. The basic design of a joystick consists of a stick

that is attached to a plastic base with a flexible rubber sheath. This plastic

base houses a circuit board beneath the stick.

I.2.4 Light Pen

A light pen (sometimes called a mouse pen) is a hand-held electro-optical

pointing device, which when touched or aimed closely at a connected

computer monitor will allow the computer to determine the position of the

pen on the screen. It facilitates drawing images and selects objects on the

display screen by directly pointing to the objects. It is a pen-like device,

which is connected to the machine by a cable.

I.2.5 Touch Screen

A touch screen is a special kind of display screen device, which is placed on the computer

monitor to allow direct selection or activation of the computer when the user touches the

screen.

I.2.6 Trackpad

A trackpad (also referred to as touchpad) is a stationary pointing device that works by

sensing the movement of fingers across a small sensitive surface and translating them into the

pointer movement on the screen. It is generally used in laptops, but can also be connected to

the PC through a cord.

NOTE: The device manufactured by Apple is referred to as trackpad while the device

manufactured by others is known as touchpad.

I.3 Speech Recognition System

Speech recognition is one of the most interactive systems to communicate with the computer.

The user can simply instruct the computer with the help of a microphone (along with speech

recognition software) what task to be performed. It is the technology by which sounds, words

or phrases spoken by the individuals are converted into digital signals, and these signals are

transformed into computer-generated texts or commands.



I.4 Digital Camera

A digital camera stores images digitally rather than recording them on a film. Once a picture

has been taken, it can be transferred to a computer system and then manipulated with an

image editing software and printed.

I.5 Webcam

A webcam (short form of web camera) is a portable video camera, which

captures live video or images that may be viewed in real time over the

network or the Internet. It is just a small digital camera that is either in-built

in your computer (in most laptops) or can be connected through a USB port.

It is normally placed on top of the PC monitor or laptop so as to capture the

images of the user while one is working on the computer

I.6 Scanners

A scanner is an input device that converts a document into an electronic format that can be

stored on the disk. Moreover, they can store images in both gray scale and color mode. The

two most common types of scanners are hand-held scanner and flat-bed scanner.

→ Hand-held Scanner: A hand-held scanner consists of light-

emitting diodes, which are placed over the document to be

scanned. This scanner performs the scanning of the document very

slowly from the top to the bottom with its light on.

→ Flat-bed Scanner: A flat-bed scanner is similar to a photocopier

machine. It consists of a box containing a glass plate on its top and

a lid that covers the glass plate. This glass plate is used for placing

the document to be scanned.

I.7 Bar Code Reader

A bar code is a machine-readable code in the form of parallel vertical

lines of varying widths. It is commonly used for labelling goods that are

available in super markets and numbering books in libraries. This code

is sensed and read by a bar code reader using reflective light. The

information recorded in the bar code reader is then fed into the



computer, which recognizes the information from the thickness and spacing of the bars.

I.8 Optical mark recognition

Optical mark recognition (OMR) is the process of detecting

the presence of intended marked responses. A mark registers

significantly less light than the surrounding paper. The optical

mark reading is done by a special device known as optical

mark reader. Generally, this technology is used to read

answer sheets (objective-type tests). In this method, special

printed forms/documents are printed with boxes, which can

be marked with dark pencil or ink. These forms are then

passed under a light source and the presence of dark ink is transformed into electric pulses,

which are transmitted to the computer

I.9 Optical Character Recognition

A scanner converts an input document into an electronic format that can be stored on the

disk. If the document to be scanned contains text, optical character recognition (OCR)

software is needed to translate the bitmap image of the text to the ASCII codes that the

computer can interpret as letters, numbers and special characters.

I.10 Magnetic-Ink Character Recognition

You must have seen special magnetic encoding using characters, printed on the bottom of a

check. The characters are printed using a special ink, which contains iron particles that can be

magnetized. To recognize these magnetic-ink characters, a magnetic-ink character reader

(MICR) is used. It reads the characters by examining their shapes in a matrix form and the

information is then passed on to the computer.

The banking industry prefers MICR to OCR as the MICR gives extra security against

forgeries such as colour copies of payroll checks or hand-altered characters on a check. If a

document has been forged, say a counterfeit check produced

using a colour photocopying machine, the magnetic-ink line

will either not respond to the magnetic fields or will produce an

incorrect code when scanned using a device designed to

recover the information in the magnetic characters.

II. OUTPUT DEVICES

An output device is an electromechanical device, which converts machine-readable

information into human-readable form. The basic functioning of output device is just the

opposite of the input device, that is, the data are 'fed into' the computer system through the

input device, while the output is 'taken out' from the computer through the output device.



II.1 Types of Output

Output is the data that has been processed into useful information. It can be displayed or

viewed on a monitor, printed on a printer or listened through speakers or a headset.

Generally, there are two basic categories of output: Hard copy output and soft copy output

→ Hard Copy refers to the recorded information copied from a computer onto the

paper or some other durable surface such as microfilm. Hard copy output is

permanent and a relatively stable form of output.

→ Soft Copy is the electronic version of an output, which usually resides in the

computer memory and/or on the disk. Unlike hard copy, soft copy is not a

permanent form of output and is not tangible, that is, it cannot be touched.

II.2 Printers

A printer prints information and data from the computer onto a paper. The quality of a printer

is determined by its resolution. Resolution is used to describe the sharpness and clarity of an

image. The higher the resolution, the better the image. For printers, the resolution is measured

in dots per inch (dpi). The more dots per inch, the better will be the quality of image.

Printers are divided into two basic categories: impact printers and non-impact printers.

Impact printers use some sort of physical contact with the paper to make a mark onto it, while

non-impact printers use techniques other than to transfer ink onto it.

II.2.1 Impact Printers

An impact printer uses pins or hammers that press an inked ribbon against the paper to make

a mark on the paper. Each hammer is embossed with a specific shape, which is transferred

onto the paper through the inked ribbon thereby producing a printed character. Some impact

printers can print only one character at a time, while others can print an entire line. The three

most commonly used impact printers are dot matrix printers, daisy wheel printers and drum

printers.

Some characteristics of impact printers are as follows:

• In impact printers, there is physical contact with the paper to produce an image.

• They are relatively cheap. The primary recurring costs for these printers are the ink

ribbons and paper.

• Due to being robust and low cost, they are useful for bulk printing.

• They can withstand dusty environment, vibrations and extreme temperature.

• They are ideal for printing multiple copies (i.e. carbon copies) because they can easily

print through many layers of paper.

• Due to its striking activity, the impact printers are very noisy.

• Since they are mechanical in nature, they tend to be slow.

a) Dot Matrix Printers



Dot matrix printer (also known as the wire matrix printer) uses the

oldest printing technology and it prints one character at a time. It prints

characters and images as pattern of dots. The speed of dot matrix

printers is measured in characters per second (cps).

b) Daisy Wheel Printer

The major drawback of dot matrix printer is that the patterns of dots that make up each

character are visible on the print produced by it, making it look unprofessional. So, to

produce professional letter quality documents, a daisy wheel printer is useful. Daisy wheel

printers produce high-resolution output and are more reliable than dot matrix printers. They

can have speed up to 90 cps. However, daisy wheel printers give only

alphanumeric output. They cannot print graphics and cannot change fonts

unless the print wheel is physically replaced. Daisy wheel printers are

slower and more expensive than dot matrix printers.

c) Drum Printers

The dot matrix and daisy wheel printers are character or serial printers, that

is, they print one character at a time. However, drum printer is a line

printer; it can print a line in a single operation. Although such printers are

much faster than character printers, they tend to be quite loud, have limited

multifont capability and often produce lower print quality than most recent printing

technologies. Line printers are designed for heavy printing applications.

II.2.2 Non-impact Printers

In this printer, the print head does not make any contact with the paper, and no inked ribbon

is required. Ink can be sprayed against the paper and then heat and pressure are used to fuse a

fine black powder into the shape of a character. The major technologies competing in the

market of non-impact printers are ink-jet and laser.

Some characteristics of non-impact printers are as follows:

• They are faster than impact printers because they have fewer moving parts.

• They are quieter than impact printers

• They possess the ability to change typefaces automatically.

• They produce high-quality graphics.

• They cannot print carbon copies.

a) Ink-jet Printers

An inkjet printer is a printer that places extremely small droplets of ink

onto paper to create an image. Ink-jet printers are costlier than dot

matrix printers, but the quality is much better. These printers can print

any shape of character, which a user can specify as they produce printed



output as pattern of tiny dots. Ink-jet printers typically print with a resolution of 600 dpi or

more. Due to the high resolution, these printers produce high quality graphics and text

printouts. They are also affordable, which appeals to small businesses and home offices.

b) Laser Printers

A laser printer provides the highest quality text and images for personal computers today. It is

a very fast printer, which operates on the same principle as that of a photocopy machine.

They are also known as page printers because they process and store the entire page before

they actually print it. Today, the resolution of most printers is 600 dpi.

They are quiet and fast, able to print 4–32 text-only pages per minute for

individual microcomputers and up to 200 pages/min for mainframes (more

than 2000 lines/min). Laser printers are often faster than ink-jet printers

but are more expensive to buy and maintain than the other printers.

c) Hydra Printer

Hybrid document reproduction apparatus (HYDRA)

printer, popularly known as all-in-one printer, is a device

that consolidates the capabilities of multiple devices in one

machine. It may include some or all of the devices like

printer, scanner, photocopier and fax machine. Following

are the features that must be considered while evaluating

these printers: Print speed, Maximum resolution, Memory

card compatibility, Scanner resolution, Fax speed

II.3 Plotters

A plotter is a pen-based output device that is attached to a computer for making vector

graphics, that is, images created by a series of many straight lines. It is used to draw high-

resolution charts, graphs, blueprints, maps, circuit diagrams and other line-based diagrams. It

is similar to a printer, but it draws lines using a pen. Plotters are

relatively expensive as compared to printers, but can produce more

printouts than standard printers. They are mainly used for computer

aided design (CAD) and computer aided manufacturing (CAM)

applications such as printing out plans for houses or car parts.

II.4 Computer Output Microfilm

Computer output microfilm (COM) is an extremely high-speed, low-cost process, which

records computer-generated information directly from the computer tape or cartridge to a

miniaturized microfilm media. The microfilm product is in fiche or roll format, which can be

duplicated rapidly and inexpensively. This process can produce data in microfilm form at a

highly significant speed from that of a paper printer. COM results in material, space and

equipment savings along with mailing costs and information retrieval savings. In addition,



hard copy prints can be made without loss of detail, when compared with the original

document. The main disadvantage, however, is that it is expensive to install COM and

microfilms cannot be read without the assistance of a special reader device.

II.5 Monitor

The monitor is the most frequently used output device for producing soft copy output. A

computer monitor is a TV-like display attached to the computer on which the output can be

displayed and viewed. Monitors are available in various sizes like 14, 15, 17, 19 and 21

inches. The larger the size of the monitor, the more expensive it is. The size of the display is

described based on two parameters: aspect ratio and screen size. Aspect ratio is the ratio of

the width of the display screen to the height, that is, the ratio of vertical points to the

horizontal points necessary to produce equal-length lines in both directions on the screen.

The screen clarity depends on three basic qualities, which are as follows:

• Resolution: It refers to the number of pixels in the horizontal and vertical directions

on the screen. A pixel (px) is the smallest portion of an image or display that a

computer is capable of printing or displaying. In medium-resolution graphics, pixels

are large, whereas in high-resolution graphics, pixels are small. The average CRT

display is currently 800 × 600 or 1024 × 768. The more dots or pixels, available to

create the image, the sharper it will be.

• Dot Pitch: It is the measurement of the diagonal distance between the two like-

coloured (red, green or blue) pixels on a display screen. It is measured in millimetres

and common dot pitches are 0.51, 0.31, 0.28, 0.27, 0.26 and 0.25 mm. Smaller the dot

pitch, sharper will be the image when displayed on the monitor. Generally, a dot pitch

of less than 0.31 mm provides clear images.

• Refresh Rate: It is the number of times per second the pixels are recharged so that

their glow remains bright. A refresh rate of 60 Hz means the image is redrawn 60

times a second. The higher the refresh rate, the more solid the image looks on the

screen, that is, it does not flicker.

II.5.1 Cathode Ray Tube Monitors

CRT is the electron beams within a monitor that move across your screen

either interlaced or non-interlaced hitting phosphor dots on the inside glass

tube. Within the CRT are three electron guns, red, green, and blue. Each of

these guns streams a steady flow of electrons, left to right, for each line of

your monitor.

II.5.2 Liquid Crystal Display Monitors

LCD is a flat display technology used in laptops, cell phones,

calculators and, flat screen displays. The LCD is made of two sheets of

a flexible polarizing material with a layer of liquid crystal solution

between the two. The LCD does not refresh like a traditional CRT

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monitor, Instead, the display is created by sending various voltages of electricity to cells of

liquid crystal causing the liquid crystal to untwist at the rate of electricity applied, generating

64 different shades per cell.

Comparison between LCD and CRT

• Size: An LCD is lightweight and compact, which saves desktop space as compared to

a CRT.

• Resolution: An LCD is designed to work in a single resolution, while CRT is designed

for many resolutions.

• Pixel Density: Pixel density of LCD is generally not as tight as the dot pitch in CRT,

but for most applications, the density is acceptable.

• Brightness: The illuminated phosphor of a CRT is not nearly as bright as what the

LCD can produce with its florescent backlight.

• Power Consumption: An LCD consumes significantly less power than CRT and has a

low emission risk. Typically, the LCD consumes approximately half of the power of a

typical CRT.

• Cost: Prices for LCD screens are quite high but they are coming down. They are still

much more expensive than a CRT.

• Viewing Angle: A CRT can be viewed at almost any angle, but an LCD is best viewed

'head on'.

• Viewing Area: The frame around the glass screen of the monitor causes the viewable

area of the screen to be smaller than an LCD.

• Weight: A CRT monitor can weigh 40 pounds or more depending on the size of the

monitor.

II.5.3 Other Types of Monitors

Although CRT and LCD displays are the most commonly used, other kinds of displays also

exist. Some of them are as follows:

• Plasma Display: A plasma display (also known as thin-panel) is constructed by filling a

gas (neon or xenon) between the two glass plates. One glass plate consists of vertical

conductors and the other consists of horizontal conductors. The advantage of plasma display

is that it has the capability of producing more than 16 million colors and is lighter and less

bulky than CRT. However, it is heavier than LCD display and requires more power.

• Thin-film Electroluminescent Display: This display is similar to the plasma display

except the fact that the space between the glass plates is filled with phosphorescent substance

(usually zinc sulfide doped with manganese) instead of gas. The main problem with thin-film

electroluminescent displays is that they require more power.

II.6. Projectors

projector is an output device, which is used to project information from a computer onto a

large screen, so that it can be simultaneously viewed by a large group of people. Projection

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display is commonly used for classroom training or conference room

or for multimedia presentations with a large audience. Like

monitors, projectors provide a temporary, soft copy output.

II.7 Electronic Whiteboard

Electronic whiteboard is an interactive presentation device that works electronically to

display digital images, drawings and text in different colors. The whiteboard is generally

mounted on the wall and is connected to a computer

(through USB, serial port or wireless technology like

Bluetooth) and a projector. The projector projects the

computer desktop on the whiteboard and the user can

interact with it using electromagnetic pens, fingers or

other pointing devices. The electromagnetic pens can

be configured to any color or width. A user can

activate programs, applications and menus, as well as

can enter text using either onscreen keyboard or

handwriting recognition utility.

An interactive electronic whiteboard can be classified into one of the following categories:

• Touch-based Whiteboard: A touch-based whiteboard allows the user to use their fingers

or other pointing devices to interact with it.

• Pen-based Whiteboard: A pen-based whiteboard mainly uses an electromagnetic pen that

alters electrical signals produced by the board and does not require batteries or power source

for its operation.

• Wii Remote, IR Pen-based Whiteboard: A Wii Remote, infrared (IR) pen-based whiteboard

works on sound electronic and optical principles. It uses Wii remote control with an IR

camera placed in front of the remote control to track dots of an infrared light, which is created

by an IR pen.

II.8 Headphones and Headsets

Headphone is an audio device equipped with a pair of speakers, which are attached to a

headstrap worn by the users. The headphones allow the users to listen only; however, some

applications like live chats, videoconferencing and telecalling services demand the user to

speak also at the same time. For such applications, headset is used instead of headphone. A

headset is a combination of one or two speakers and a microphone with both the speaker and

the microphone attached to a headstrap. The speaker(s) allows the person to hear the

conversation and the microphone allows to communicate with the person on the other end



II.9 Terminals

Computer terminal is a special unit that can perform as both input and output. A terminal is

an I/O device that uses a keyboard for input and a monitor for output. Hence, a terminal is

also known as video display terminal (VDT). The terminals can be categorized into the

following types

• Dumb Terminal: It refers to a terminal that has no processing or programming

capabilities. It is designed to communicate exclusively with a host computer. Usually,

it consists of a screen and keyboard used to access a host computer.

• Smart Terminal: Smart terminal has built-in processing capability and memory, but

does not have its own storage capacity. In comparison to the dumb terminal, smart

terminal can communicate and retrieve the data and can perform a limited processing

of its own, that is, editing or verification of the data.

• Intelligent Terminal: An intelligent terminal has memory and in-built

microprocessors, hence also known as user-programmable terminal. This terminal can

independently perform a certain number of jobs without even interacting with the

mainframe. Although they are intelligent terminals, some workstations are designed

without disk drives. Due to this, the restricted data cannot be downloaded or copied.

Documents

COMPUTER INPUT/OUPUT DEVICESdata.over-blog-kiwi.com/0/64/15/65/20140127/ob_529024...Topic: Input/output devices Par DZEUGANG PLACIDE Visit for further learning tools for ICT & Comp