Module 3: Computer Peripheral Devices
Unit 1: Input Devices
Content
1.0 Introduction
In the previous modules of this course, you have learned about
various hardware parts of computer systems, as shown in the John Von
Neumann architecture. Peripheral devices, which involve input and
output devices, are significant parts of this standard architecture. The
peripheral devices are connected externally to the computer's system unit
through appropriate interfaces and ports.
2.0 Intended Learning Outcomes
At the end of this Unit, you will be able to:
Understand the input devices and the functions in the
computer system
Identify various kinds of input devices
3.0 Main Content
3.1 Description of Input Devices
Input devices are parts of the computer system that enable the users to
enter data and the required control parameters into the computer.
Subsequently, the input data is converted and translated into a computer-
readable format for subsequent processing by the central processing unit.
Input devices can be categorized into pointing, scanning, wireless, and cable
devices. Pointing input devices are used to move a cursor on the screen.
Examples of these include the mouse, trackball, and touchpad. The category of
scanning input devices is Optical Mark Recognition (OMR), scanners, Optical
Character Recognition (OCR) devices, barcode readers, among others. These
pointing input devices can sense and read characters directly on papers and
other materials. Bar code readers are often used to scan bar code items in
supermarkets and different types of industrial products in the supply chain line.
Some of the input devices include the keyboard, mouse, touchpad, webcams,
microphones, joysticks, and image scanners. Figure 27 shows Computer with
Peripheral Devices.
Figure 1 Computer with Peripheral Devices
3.2 Keyboard
The keyboard is the primary and commonly used data entry device for
different computers. Like the old typewriter machines, the keyboard is used
to enter data into the computer by typing the necessary alphanumeric keys.
There is a total of 104 numeric, alphabet, and function keys. The keyboard
can be connected to the system unit via cable or Bluetooth wirelessly.
Essentially, the keyboard typing keys include the following classes
Upper and lower case alphabet keys from A-Z and a-z, respectively
Numeric keys from 0 to 9
Special 12 function keys for specific purposes
control (Ctrl) keys
cursor and screen control keys are Arrow keys, page up, page down
Alternate (Alt), Escape (Esc), Home, End, Insert, Delete
Enter, backspace, num-lock, caps lock, shift, space bar, tab, scroll
lock, sleep, print screen
Figures 28 and 30 show the illustration of the computer keyboard.
Figure 3 Computer keyboard
3.3 Mouse
A mouse is an input pointing device rolled over a smooth surface to control
Figure 2 Description of computer keyboard
the cursor on the computer screen through its speed-controlled sensor, and
operational clickable buttons on the left, middle, and right parts. The
functions of the buttons can be customized to select and open files or
objects. Figures 30 and 31 show the wired and wireless mice.
Figure 4 Wireless Mouse
Figure 5 Mouse
3.4 Image scanners
The image scanner is an input device that optically scans printed materials,
objects, images, and documents and thereafter converts and stores them in a
digital format. The scanned document be edited for further application.
Figure 32 shows a scanner.
Figure 6 Scanner
3.5 Track Ball
A trackball is a pointing device that holds a small ball held in its sensor-
based socket. The sensor detects the rotational movement of the ball about
its two axes. The device operates exactly like an upside-down mouse but
uses space to rotate its ball. As the trackball remains stationary and the user
moves the ball in various directions, it reflects activity on the screen, as
shown in Figure 33.
.
Figure 7 Track ball
3.6 Light Pen
A light pen is a light-sensitive input device that can be used to point and
write or draw directly on the visual display unit, monitor, and screen. Light
pen to detect raster on the screen as it passes on it with high precision. The
light pen functions well like the touchscreen devices, as shown in figures 34
and 35.
Figure 9 Light pen Figure 8 Light pen on IPAD
3.7 Headsets and Microphone
Headsets or microphones are a kind of computer voice input devices that can
record sounds by transmitting and converting human speech or voice into
electrical signals. The computer processes this electrical signal and the word
is recognized. Application areas include customers service, religious
programmes, and technical support centers, where the users can
communicate with clients while entering or typing into a computer. Figure
36 shows a typical computer microphone.
Figure 10 Computer microphone
3.8 Optical Character Reader
Optical character recognition or optical character reader (OCR) uses a low-
frequency light source to detect and convert drawn images, alphanumeric
characters, and printed text into machine-encoded text, pictures, or scanned
documents. The OCR, which operates as a scanner, absorbs light from the
dark areas and is reflected by the light areas. Subsequently, it reflects and
receives the light from the photocells, as shown in figure 37.
Figure 11 Barcode Reader
3.9 Bar Code Reader
A barcode reader is an optical scanning device that is connected to a
computer to read printed barcodes and decode the hidden data. The barcode
reader, which functions like a flatbed scanner comprises a light source, a
lens, and a light sensor translating optical impulses into electrical signals.
Most barcode readers contain decoder circuitry that can analyze the image
data via the sensor and send the contents of the barcode to the scanner
output port.
Figures 38 and 39 show a barcode reader reading data that is coded into
white and black lines.
Figure 12 Bar code reader
Figure 13 Bar code scanner
4.0 Conclusion
Several computer data input devices have been discussed. The input
devices are part of peripheral devices that help users enter data into
the computer system via diverse port interfaces. Upon reception, data
will be processed by the CPU for further action. Some standard input
devices are keyboard, mouse, scanner, optical character reader, and
barcode reader, among others.
5.0 Summary
In this Unit, you have learned about some standard data input devices.
6.0 Self-Assessment Exercises
i. What do you understand by peripheral devices?
ii. Explain the function of a barcode reader as an input device
Answers
i. Peripheral devices, which involve input and output devices,
are significant parts of this standard architecture. The
peripheral devices are connected externally to the system unit
of the computer through appropriate interfaces and ports.
ii. A barcode reader is an optical scanning device that is
connected to a computer to read printed barcodes and decode
the hidden data. The barcode reader, which functions like a
flatbed scanner comprises a light source, a lens, and a light
sensor translating optical impulses into electrical signals.
7.0 References and Further Reading
"Logitech M570 Wireless Trackball Mouse Review: Unconventional
Features". Archived from the original on 2020-08-15
Alapetite, A (2010). "Dynamic 2D-barcodes for multi-device web
session migration including mobile phones". Personal and Ubiquitous
Computing. 14 (1): 45–52. doi:10.1007/s00779-009-0228-5. S2CID
10202670
Unit 2: Output Devices
Content
1.0 Introduction
You have learned about input devices in Unit 1. This Unit 2 will learn more
about computer peripheral devices, essentially, the output devices. These are
the devices used to display, in human-readable form, the output of any task
carried on the computer.
2.0 Intended Learning Outcomes
At the end of this Unit, you will be able to:
Identify some output devices often used to enter data into
computers
Differentiate between input and output devices
3.0 Main Content
3.1 Description of Output Devices
An output device is any peripheral hardware connected to a
computer either wired or wireless to display, project, or physically
reproduce the results of data processed by a computer. It converts
electronic information into a format which can be understood by
humans.
What differentiates an input from an output device is that the input
device transfers data to the computer, whereas the output data
receives data from the computer. Input device usage is mandatory to
operate the computer. On the other hand, output devices may be
optional.
Conventionally, the output devices can be grouped into data, print,
visual, and sound hardware. Thus, various output hardware include
visual display unit (monitor or screen), printer, plotter, headphones,
computer speakers, projector, GPS, sound card, video card, braille
reader, and speech generating machine.
3.2 Visual Display Unit
The visual display unit (VDU), popularly known as a monitor or display
screen, is the primary and well-known output device that displays output
contents as picture elements (pixels) on the computer screen. These output
contents include text, video, images, etc. The VDU looks much like a TV
screen, and shares similar resolution parameters.
The number of pixels determines the resolution of the monitor. The monitor
resolution, smoothness, or picture clarity increases with more pixels. The
two types of monitor screens are cathode ray tube monitors (CRT) and flat-
panel screen monitors.
Cathode Ray Tube monitors, which were manufactured using old CRT
technology, applied phosphorescent dots to generate pixels that form
displayed images. CRT monitor screens, which were the same as the old TV
CRT technology, were usually large and consumed more power. Figures 40
and 41 show LCD and CRT visual display units respectively.
Figure 14 LCD visual
display unit
Figure 15 CRT visual display unit
Flat Panel Screen Monitors
Flat-panel screen monitors, which implement a thin panel design instead of
CRT technology, are lighter, thinner, and portable. They use liquid crystals
or plasma technology to generate output as light passes through liquid
crystals to form the required pixels.
The three types of Flat Panel screen monitors are Liquid Crystal Devices
(LCD) monitors or Non-emissive displays, Light Emitting Diode (LED)
monitors or Emissive displays, and Plasma monitors. Let us explain these
three types of monitor screens.
a) Liquid Crystal Devices (LCD) monitors or Non-emissive displays
This type of flat panel display implements the light-modulating
properties of liquid crystals. This technology is also replicated in LCD
televisions, aircraft cockpit displays, ship cocktail screens, etc. An LCD
monitor is more energy-efficient and users’ friendly. It is safer to
dispose of the CRT monitors.
b) Light Emitting Diode (LED) monitors or Emissive displays
Although the technologies of LCD and LED are similar. The LED
technology of LED is more advanced than the LCD monitor. The
LED monitors are lighter, thinner, and less expensive. These
monitors are more reliable as they have a more broad dimming range
of backlighting.
c) Plasma monitors
The picture elements in the plasma screen monitors are illuminated
by a tiny bit of charged gas or plasma similar to a small neon light.
These monitors are thinner, brighter, and better in performance than
the Cathode ray tube and liquid crystal display monitors.
3.3 Printing Devices
The printing devices are specialized computerized machines that can
print information permanently on materials of different forms. They
are usually stand-alone systems connected to computers via cable,
wirelessly or by cloud. Examples of printing devices include printers,
plotters, and 3D printers, among others. This section discusses some
printing devices.
3.3.1 Printers
A printer is the second most common type of output device that
permanently transfers the processed data from the computer into a printed
format and thereby produces text or images hardcopy output on paper.
Today, different printers can print texts, photos, and graphics objects in
coloured, monochrome, and black and white. Printers used in homes and
offices have high dots per inch (DPI), generating high-quality images.
The printers are classified into Impact and Non-Impact printers.
a) Impact printer
This is an old type of printer that noisily prints characters by striking on the
ribbon and thereby imprint on the paper.
The impact printers can either be the character or line printers.
i. Character printers
These printers are capable of printing text, and a single character at a
time in the average speed is up to 300 lines per minute. The different
character printers include chain, band, dot matrix, and daisy wheel
printers. The commonly used printers are dot matrix and daisy wheel.
ii. Line Printers
Line printers can print and display output texts line by line. The two types of
line printers are drum printers and chain printers. The drum printer has high
speed and can print up to 300 to 2000 lines per minute.
b) Non-Impact printer
The non-impact printers can print without striking the ribbon. These include
laser printers and inkjet printers.
i. Laser Printers
Laser printers use a photoelectric drum, powdered ink, and laser light to
produce dots to form the characters for printing. When a print command is
given, a laser beam draws the document on a selenium-coated drum using an
electrical charge, providing a clean copy of the image on the paper. Since
ink is not used, they have fewer smearing problems than an inkjet printer.
A laser printer uses the same technology and procedures as a copying
machine. Figures 42 and 43 show LaserJet printers.
ii. Inkjet Printers
This printer generates output by spraying ink droplets onto the paper through
a small nozzle. Inkjet printers are the most widely used type of printer.
There are expensive and inexpensive models available in the market. It was
the most common type of printer due to limited available technology in the
olden days. The printers are less expensive.
Figure 16 LaserJet Printer
Figure 17 Coloured Epson Printer
3.4 Graph Plotter
A plotter output device, which is similar to a printer but usually bigger, can
be used to draw large high quality, images, pictures, and vector graphics.
A plotter is used to generate and draw hardcopy on paper large drawings,
architectural blueprints, engineering drawings, graphic cards, cadastral
maps, and satellite imageries. Figure 44 shows a graph plotter.
Figure 18 Graph Plotter
3.5 Computer Speakers
Computer speakers are one of the most common output hardware used with
a computer. The speakers receive audio as input from the computer via a
sound card. The internal amplifiers of the speaker can be used to control or
vary the volume or the amplitude of the sound. The connection of external
speakers can be used to enhance the volume and other in-built parameters of
the sounds. Figure 45 shows computer speakers.
Figure 19 Computer speakers
4.0 Conclusion
Computer output hardware is pretty crucial in showing and revealing the
results of processing by the CPU. Some standard output devices are
visual display units, printers, and output accessories. A printer is a
peripheral output device that produces a hard copy of graphics or text
from a computer, usually on paper. While most output is human-readable,
bar code printers are an example of expanded use for printers. Different
printers include 3D printers, inkjet printers, laser printers, and thermal
printers.
5.0 Summary
In this Unit, you have learned about some standard computer output devices.
Their usage enables the users to view and appreciate the results of
processing.
6.0 Self-Assessment Exercises
i. What differentiates input from output devices?
ii. In general, how would you describe output devices?
Answers
i. Input devices transfer data to the computer, whereas the output
data receives data from the computer. Input device usage is
mandatory to operate the computer. On the other hand, output
devices may be optional.
ii. An output device is any peripheral hardware connected to a
computer either wired or wireless to display, project, or
physically reproduce the results of data processed by a
computer. It converts electronic information into a format
which can be understood by humans.
7.0 References and Further Reading
Morley, Deborah (April 2007). Understanding Computers: Today &
Tomorrow, Comprehensive 2007 Update Edition. Cengage Learning. p.
164. ISBN 9781305172425.
https://www.tutorialspoint.com/basics_of_computer_science/
basics_of_computer_science_types.htm
https://www.classmate4u.com/output-devices-of-computer/
