Input and Output Devices

Input and Output Devices
Unit A451:
Computer systems and programming
Section 2: Computing Hardware
4/5: Input and Output Devices
Input and Output devices
Candidates should be able to:
(a) understand the need for input and output devices
(b) describe suitable input devices for computers
(c) describe suitable output devices for computers
(d) discuss input and output devices for users with specific needs.
The Need for Input / Output Devices
• Input devices are needed so that data can
be entered into a computer system, to be
stored or processed.
• Some input devices are manual, such as a
keyboard or mouse, and some are
automatic, such as a barcode reader or a
webcam.
(o) understand the need for input and output devices
Input Devices - Mouse
• The mouse is used to control the movement of a pointer on the
screen when it is moved horizontally over a flat surface. Buttons
on the mouse let you select options from menus and drag
objects around the screen etc.
• Advantages: Ideal for use with desktop computers. Usually
supplied with a computer so no additional cost. All computer
users tend to be familiar with using them.
• Disadvantages: They need a flat space close to the computer.
The mouse cannot easily be used with laptop, notebook or
palmtop computers when not near a flat surface.
(p) describe suitable input devices for a wide range of computer controlled situations
Input Devices - Tracker ball
• A tracker ball is like an upside-down mouse because the
user rotates the ball and the main body part stays still. It
has buttons for selecting items and menus etc. like a
standard mouse.
• Advantages: Does not need a flat space close
to the computer. Can be useful with laptops
as they can be built into the computer
keyboard or clipped on.
• Disadvantages: Not supplied as standard so
an additional cost and users have to learn
how to use them
(p) describe suitable input devices for a wide range of computer controlled situations
Input Devices - Keyboard
• A keyboard uses labelled buttons as input switches. The
standard QWERTY keyboard is the commonest way to enter
text and numerical data into a computer. Alternatives to fixed
layouts include overlay keyboards and touch screen keyboards,
both allowing easy customisation.
• Advantages: Reliable for data input of text and numbers.
Usually supplied with a computer so no additional cost.
Specialised keyboards are available for particular purposes.
• Disadvantages: Slow to enter data and prone to typographical
errors with new users. Slow for accessing menus etc. and
difficult to use if you want to move objects around the screen.
Difficult for users unable to use a keyboard through paralysis or
muscular disorder.
(p) describe suitable input devices for a wide range of computer controlled situations
Input Devices – Bar Code Scanner
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A barcode uses a pattern of dark and light parallel lines of different
thickness to encode a number. They also include a checksum digit to ensure
the barcode has been read correctly. The scanner scans a beam of laser
light over the barcode and detects the distinctive pattern of reflected light
from the barcode.
Suited to: quickly reading numerical codes
from labels and packaging.
Advantages: Fast and accurate capture of
numerical data.
Disadvantages: Limited to numerical data.
Can increase packaging costs as multi-pack
products require a different barcode.
If the barcode is misread, the data may have
to be entered manually.
(p) describe suitable input devices for a wide range of computer controlled situations
Input Devices - Optical Mark Reader (OMR)
• Suited to: quickly reading numerical data entered as marks on a
pre-printed sheet such as a lottery ticket form or a class register /
test paper
• Advantages: Fast and accurate.
• Disadvantages: Limited to numerical data.
(p) describe suitable input devices for a wide range of computer controlled situations
Input Devices - Voice recognition
• Suited to: situations where a microphone can be used to input text
or make selections from menus.
• Advantages: Voice recognition telephone menu systems save on
staffing costs. Can be quicker than entering text via a keyboard.
Idea for disabled users and hands-free applications. Can be used for
security.
• Disadvantages: Many systems require the software to be trained to
recognise the user's voice. There can be errors when the software
does not recognise words, either due to regional accents,
background noise or the limitations of the software.
(p) describe suitable input devices for a wide range of computer controlled situations
(p) describe suitable input devices for a wide range of computer controlled situations
Output Devices – Laser Printer
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Powdered plastic toner is charged and attracted to paper
that has a pattern of the opposite charge matching the
required image/text. The toner is then melted to bond with
the paper.
Suited to: situations were high quality, fast printing is
required, but not of photographic quality.
Advantages: Printing costs per page are low
and printing is fast. Double sided and colour
printing are available.
Disadvantages: A higher initial
purchase cost and printing is not
possible on glossy photographic paper,
or some plastics.
(q) describe suitable output devices for a wide range of computer controlled situations
Output Devices – Inkjet Printer
•Fine nozzles in a printer head spray microscopic drops of coloured
ink onto the paper surface, line by line. Basic models use 3 colours
plus black while premium models have up to 6 colours.
•Suited to: situations were photographic quality printing is
required and speed is not essential.
•Advantages: Purchase costs are very low and these printers
offer very high quality borderless colour printing of photographs
on both plain and glossy papers.
•Disadvantages: Slow printing speeds
and the printing costs per page are high
as the ink cartridges are relatively
expensive to replace.
(q) describe suitable output devices for a wide range of computer controlled situations
(q) describe suitable output devices for a wide range of computer controlled situations
Output Devices – Monitors
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Cathode Ray Tube (CRT) models are increasingly being replaced by flatscreen Liquid Crystal Display (LCD) models.
Suited to: displaying text, images or video in a wide range of sizes, colours
and resolutions. In a laptop or Smartphone the screen is built into the
device and therefore portable. Touch screens allow the monitor to become
an input device.
Advantages: allows a computer to output a wide range of static and moving
information in up to 16 million colours and at a high resolution. A wide
range of monitor sizes are available, from a few cm up to several metres.
Disadvantages: CRT models are heavy and therefore non-portable, as well
as being less power efficient and far more bulky. LCD screens, unless glassfronted, are easily damaged.
(q) describe suitable output devices for a wide range of computer controlled situations
Output Devices – LED (Lights)
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LEDs (Light Emitting Diodes) can be connected to a computer and respond
to electrical signals which tell them to switch on and off. Control devices
such as lights, buzzers and motors are used when the computer is
controlling a situation such as traffic lights.
Suited to: simple warnings and indicators although LED's can be arranged to
form segments of a text or numeric display.
Advantages: LED's use little power so can usually be powered directly from
a computer system. They can provide a warning for users with hearing loss
who might not be able to hear the error beeps produced by the internal
speaker.
Disadvantages: The bulb may break or wear out and need replacing. There
may be a loose connection which means the light doesn't switch on even if
the circuit or control program is correct .
(q) describe suitable output devices for a wide range of computer controlled situations
Question 1 – Exam Practice
• A shopping centre uses several remote-controlled
CCTV cameras for security. An operator uses a
computer to watch, control and record the output of
the cameras.
• Describe one input device the system could use and
why it is required (2 marks)
• Describe one output device the system may use and
why it is required (2 marks)
(q) describe suitable output devices for a wide range of computer controlled situations
Devices for
Blindness and visual disabilities:
• For partial blindness, adjusting screen contrast options and
magnifying parts of the screen.
• For complete blindness, text recognition and screen reading
software to read out screen contents. (relies on embedded tags
for image knowledge)
• Braille printers can print the tiny bumps used in Braille directly
onto paper, also Braille keyboards to allow text input.
• Voice recognition software and a microphone can be used to
input text and control some computer operations.
• GPS equipped Smartphones with voice recognition, allows blind
person to walk about and be guided through their surroundings.
(r) discuss input and output devices for users with specific needs.
(r) discuss input and output devices for users with specific needs.
Devices for
Deafness and hearing disabilities:
• Videophones and video conferencing allow sign language
and lip reading to be used in distance conversations using
video.
• Digital hearing aids can amplify and clarify sounds, as well
as linking to induction loop hearing systems in telephones
or public building.
• Flashing lights can be used to replace auditory signals and
alarms as outputs.
• Subtitles can be included in video content and some
software can output subtitles in real time from spoken
audio.
(r) discuss input and output devices for users with specific needs.
Devices for
Physical disabilities:
• A joystick can also be used to control devices such as an electric
wheelchair
• A puff-suck switch is operated by sucking or blowing through a tube.
It can used as a replacement for clicking buttons on a mouse.
• A foot mouse replaces a conventional mouse and is operated by the
feet. Usually one foot controls the movement and the other one the
clicking of the buttons.
• Motors in prosthetic limbs can be controlled by linking sensors to
severed nerves.
• An eye tracking camera can be located on the face or on the
computer screen. It can detect where on the screen the user is
looking and therefore control a cursor. Blinking can then used to
operate mouse clicks.
(r) discuss input and output devices for users with specific needs.
Question 2
The school wants the computer systems to
be more accessible to students with
disabilities.
Describe, with examples, one input and
output device available for students with
disabilities. (4 marks)
(r) discuss input and output devices for users with specific needs.
(r) discuss input and output devices for users with specific needs.
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