Unit A451: Computer systems and programming · Unit A451: Computer systems and programming Section...

Unit A451: Computer systems and programming

Section 2: Computing Hardware 4/5: Input and Output Devices

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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

(o) understand the need for input and 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.

Input Devices - Mouse

(p) describe suitable input devices for a wide range of computer controlled situations

• 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.

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

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.

Input Devices – Bar Code Scanner


• 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.

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.

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.

Output Devices – Laser Printer

(q) describe suitable output devices for a wide range of computer controlled situations

• 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.

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.

Output Devices – Monitors

• Cathode Ray Tube (CRT) models are increasingly being replaced by flat-screen 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 glass-fronted, are easily damaged.


Output Devices – LED (Lights)

• 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 .


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)


Devices for Blindness and visual disabilities:

(r) discuss input and output devices for users with specific needs.

• 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.

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.

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.

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)

Unit A451: Computer systems and programming · Unit A451: Computer systems and programming Section...

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