Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware.
Although there are many adaptations that can be made to computer hardware so that those with disabilities can access computers more readily, designers of computer hardware should be aware of accessibility features that can be incorporated in the initital design and development stages.
Most computer hardware is not seen by users as it is embedded within the devices. A typical personal computer, the computer hardware familiar to most people, consists of a case or chassis and the following parts:
- a motherboard
- power supply
- storage and video display controllers
- removable media devices
- internal storage
- a soundcard
- networking devices
In addition, hardware devices can include external hardware components. The following are either standard or very common peripheral devices identified with a computer system:
- Text input devices
- Pointing devices
- Gaming devices
- Game controller
- Image and video input devices
- Audio input devices
- Image and video output devices
- Monitor / Display
- Audio output devices
- Assistive technology devices
- Braille embosser - a device that is the Braille equivalent of a printer. It embosses patterns on paper or thin card to produce tactile Braille symbols.
- Braille display - an electronic device that connects to a computer with a display consisting of pins that move up and down to represent the dots of a Braille cell. The display is used to represent a line of text on a computer screen.
Problems encountered by disabled people and the ageing population using computer hardware
Blind and Partially Sighted
Blind and partially sighted users often have problems with reading the display and seeing other visual details on the screen. The size of the screen, screen resolution, availability of colours, fonts and font sizes will all have an impact on how blind and partially sighted users access a computer.
Blind and partially sighted computer users may have difficulties using input devices such as a mouse, due to the size and movement of the cursor and the difficulty in interpreting spatial relationships, such as layout. The option to use keyboard input instead of a pointing device is an essential feature for blind and partially sighted users.
Any textual documentaton that comes with computer hardware for installation or instructional purposes will be problematic for blind and partially sighted users.
Sound is often used to alert the computer user of an error, to signify task completion or that an input is required. For those who cannot hear the sounds, alternatives may be required. The increasing use of multi-media output means that more consideration should be given to the needs of hearing impaired users.
Physically impaired users often have difficulty in using input devices or in handling storage media. Providing a means to connect an alternative keyboard would often help people with a severe physical impairment. However, connecting peripheral hardware devices to a computer may also cause problems if connection terminals are not within easy reach of the user.
People who have a learning disability such as dyslexia, may find difficulty in reading and deciphering text both on a keyboard and on a screen.
Some users with cognitive impairments may struggle with the concept of what a keyboard or mouse is for. For example, a user may be an incredibly agile and fast mouse user, but has no interest or desire to use a keyboard. In this case a number of hardware or software solutions may help to overcome these difficulties.
People with the specific condition called ‘photo-sensitive epilepsy’ may find that moving or flickering light can cause problems, and this can include computer screens. Only a minority of people with epilepsy are in fact photo-sensitive. For many others, the problems they experience while using a computer are not due to the movement, or “flicker”, of the screen image but rather to other causes such as eye strain and general stress.
Overly complicated installation or instruction manuals can also prove to be a challenge for some people with cognitive impairments.
Elderly people can experience a range of the problems mentioned above due to reduced physical, sensory or cognitive abilities that come with advancing age. It is also known that because some elderly people can have trouble reading and are slower to understand and learn new things they tend to view computers as complex machines that are fast and hard to understand. They have a natural tendency to distrust computers, and a certain reluctance to begin working with them.
- The surface of the controls should not contain any material which may cause an allergy
- Controls should be operable with one hand
- Controls should be placed so they could easily be reached by a person in a wheelchair
- Controls should be well spaced so that they are not activated by mistake
- Controls should be tactilely discernible without activating them
- Controls should be tactilely marked so that the control setting can be easily identified by touch
- For controls that do not have any physical travel, audio or tactile feedback should be provided so the user knows when the control has been activated (e.g. a toggle switch or a push-in/pop-out switch)
- The size, shape and surface of controls should be designed so that they are easily grasped
- The labels on the controls should be high contrast, clear, and as large as is possible
According to the Nordic Cooperation on Disability (1998) operation of a control should not:
- "require more power than 2 Newton"
The Design Considerations Task Force of the Industry/Government Cooperative Initiative on Computer Accessibility (1988) states that push button controls should:
- require "less than 100 grams of pressure"
Keyboards and keypads
Basic ergonomic features
- All commands and options can be accessed by using the keyboard. This could be provided by operating the arrow keys or by keyboard equivalents for all menu items
- The keyboard should be detachable and have a sufficiently long cable, approximately 1.5 metres (Nordic Cooperation on Disability, 1998), so that it can be placed according to the user's needs
- According to the Nordic Cooperation on Disability (1998) the keyboard should be of a low-profile type, i.e. the height of the key-row beginning with A-S should be not greater than 30mm
- There should be good friction between the keyboard and the desktop
- The colour of the keytops should be matt
- The surface of the keytops should be concave
- The user should receive a tactile and audible feedback when pressing a key. It should be possible to adjust and switch off the audible feedback
Localisation of keys
- Groups of keys (alphanumeric, numeric, function keys) should be separated by distinct spaces, with a distance of at least half a key (This requirement is not applicable on laptops.)
- Groups of keys should be distinguished by different colours on the key tops, but in a way that colour-blind persons may discern the colours.
- The F and J keys on the alphanumeric keyboard, and the 5 key on the numeric keyboard, should be marked with a tactile identification, preferably in the form of a ridge on the keytop edge nearest to the user.
- Frequently used keys, such as Enter, Shift, Escape, Ctrl, Backspace etc., should be placed and have a shape that differ from other keys so that they are easy to find.
Identification of keys
- The contrast between the colours of the characters and the background of the keytop should be the best possible
- The height of the characters of the alphanumeric and numeric keys should, according to the Nordic Cooperation on Disability (1998), not be less than 4mm.
- The height of the characters of the other keys should not be less than 4mm, if there is available space.
- The text on the keys should be printed in sans-serif font
- Text should not be printed in the colours red or green
- The user should be allowed to customise the keyboard with respect to features such as repeat rate, key activation delay, delay between acceptance of two consecutive key presses, minimum time for pressing a key before the key repeat begins, and serial instead of multiple simultaneous keystrokes etc.
- If key repeat is supported, the delay before repeat should be adjustable to at least 2 seconds per character (IBM, 2008)
- If sufficient space is available, shift keys (upper and lower case, ctrl, alt etc.) should be duplicated, one on each side of the keyboard, and be placed symmetrically
- The keyboard should be designed to provide sufficient space to allow the user to mount a keyguard
- The system should allow the connection of two keyboards, which could be used simultaneously, for instruction purposes
According to the Nordic Cooperation on Disability (1998) the power to press a key should be:
- "between 0.3 and 0.6 Newton"
- The user should be allowed to execute pointing functions from the keyboard
- Provide the user with the facility for modifying cursor speed, distance and double-click interval
- The operation of a pointing device should not require two simultaneous hand movements
- The power needed to operate a pointing device should be between 0.3 and 0.6 Newton (Nordic Cooperation on Disability, 1998)
Drives and removable media
- Mechanisms for inserting and removal of drives and removable media should require a minimum of muscular strength, range of motion, reach and movement precision. Twist lock mechanisms should be avoided
- The user is alerted of incorrect insertion
- Screens should have a frequency greater than 2Hz and lower than 55Hz to avoid flicker (IBM, 2008)
- The typeface should be clear and legible
- The display should have good contrast
- Minimise glare on the display
- The display can be separated from the device so it can be placed in an accessibile position or replaced by another better suited to the user's needs (This requirement is not applicable on laptops.)
- The display provides an easy mechanism for altering its angle, height etc.
Colour and contrast
- Colour is used as an enhancement
- Users should be able to select and adjust the colours and contrast used on the display
- Audio output is supplemented by captioning or subtitles
- Signals from the basic system, such as alarms, warnings, status lamps and error messages, should have the following characteristics:
- Alternative forms - auditory, visual or tactile, allowing both visually and hearing impaired persons to adapt the signalling to their perceptive characteristics
- The volume, and if possible also the pitch and frequency, of auditory output should be adjustable
- Visual signals should be placed where they are easily perceived
- There is an option to reset the volume to a default level
- Warnings and similar alert messages must remain stable for a sufficiently long time to be discovered by the user. A way of avoiding problems is to let the message remain until dismissed by the user
- Internal speaker units are located at the front of the computer and directed towards the user
- An industry standard connector for headphones or personal listening devices should be provided
- Provide tactile indication on any plug or insert and its corresponding connection point
- Provide a bevel around the slot or connection point
- Serial and parallel interface connectors, data buses, keyboard connectors and other data transfer mechanisms such as infrared technology or radio, should follow existing standards or de facto standards
- Connection points e.g. USB ports are located on the front of the computer
- A system purchased with the expectation that it will now or in the future be used by a user who needs an assistive device should have the maximum number of serial ports, parallel ports and expansion slots
- The controls of the printer should, where applicable, satisfy the requirements stated in Controls (see above)
- Audible signals emitted by the printer should satisfy the requirements stated in Audio output (see above)
- Alarms from the printer should appear on the display of the workstation
Instruction manuals / Documentation
Manufacturers should provide access to information and documentation including user guides, installation guides and product support communications.
- Use simple clear concise language
- Have a table of contents and a good index
- Be task orientated
- Provide alternate formats (e.g. audio tape, large print)
- Provide alternate modes of delivery (e.g. fax, relay service, TTY, Internet posting)
- Use a typeface with good legibility
- Information contained in pictures should also be explained in the text
- Provide information on what to do if the computer hardware does not work correctly, or the user is unable to understand the instructions (e.g. a telephone help number)
- 36 CFR Part 1194 [Docket No. 2000-01] RIN 3014-AA25 (2000) Electronic and information technology accessibility standards - Section 508
- EG 202 116 (2002) Human Factors (HF); Guidelines for ICT products and services: Design for all
- ETSI TR 102 068 (2002) Human Factors (HF): Requirements for assistive technology devices in ICT
- INCITS 154 (1988) Office machines and supplies - Alphanumeric machines - Keyboard arrangement (formerly ANSI X3 154 (1988) (R1999))
- ISO 9241-4 (1998) Ergonomic requirements for visual display terminals - Part 4: Keyboard requirements
- ISO 9241-11 (1998) Ergonomic requirements for visual display terminals - Part 11: Guidance on usability
- ISO 9241-300 Ergonomics of human-system interaction - Part 300: Introduction to electronic visual display requirements
- ISO 9241-302 Ergonomics of human-system interaction - Part 302: Terminology for electronic visual displays
- ISO 9241-303 Ergonomics of human-system interaction - Part 303: Requirements for electronic visual displays
- ISO 9241-304 Ergonomics of human-system interaction - Part 304: User performance test methods
- ISO 9241-306 Ergonomics of human-system interaction - Part 306: Field assessment methods for electronic visual displays
- ISO 9241-307 Ergonomics of human-system interaction - Part 307: Analysis and compliance test methods for electronic visual displays
- ISO 9241-410 (2008) Ergonomics of human-system interaction - Part 410: Design criteria for physical input devices
- ISO/FDIS 9241-305 Ergonomics of human-system interaction - Part 305: Optical laboratory test methods for electronic visual displays
- ISO/IEC 10741-1 (1995) Information technology - User-system interfaces - Dialogue interaction - Part 1: Cursor control for text editing
- ISO/IEC 14755 (1997) Information technology - Input methods to enter characters from the repertoire of ISO/IEC 10646 with a keyboard or other input device
- ISO/IEC 15411 (1999) Information technology - Segmented keyboard layouts
- ISO/IEC 15412 (1999) Information technology - Portable keyboard layouts
- Nordic guidelines for computer accessibility (1998) 2nd edition
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