In human-computer interaction, computer accessibility (also known as Accessible computing) refers to the accessibility of a computer system to all people, regardless of disability or severity of impairment. It is largely a software concern; when software, hardware, or a combination of hardware and software, is used to enable use of a computer by a person with a disability or impairment, this is known asAssistive Technology.
There are numerous types of impairment that affect computer use. These include:
· Cognitive impairments and learning disabilities, such as dyslexia, ADHD or autism.
· Visual impairment such as low-vision, complete or partial blindness, and color blindness.
· Hearing impairment including deafness or hard of hearing.
· Motor or dexterity impairment such as paralysis, cerebral palsy, or carpal tunnel syndrome and repetitive strain injury.
These impairments can present themselves with variable severity; they may be acquired from disease, trauma or may be congenital or degeneration in nature.
Accessibility is often abbreviated a11y, where the number 11 refers to the number of letters omitted. This parallels the abbreviations of internationalization and localization as i18n and l10n respectively.
Special needs assessment
People wishing to overcome an impairment in order to use a computer comfortably and productively may require a "special needs assessment" by an assistive technology consultant (such as an occupational therapist or clinical scientist) to help them identify and configure appropriate assertive hardware and software.
When a disabled person is unable to leave their own home, it may be possible to assess them remotely using remote desktop softwareand a web cam. The assessor logs on to the client's computer via a broadband Internet connection and then remotely makes accessibility adjustments to the client's computer where necessary. Additionally, the assessor is able to observe their computer usage.
Cognitive impairments and illiteracy
The biggest challenge in computer accessibility is to make resources accessible to people with cognitive disabilities - particularly those with poor communication skills - and those without reading skills.
Their further development relies on public domain icons being available. Many people with a learning disability learn and rely on proprietary symbols. They thus become tied to particular products. The copyright owners are generally unwilling to release them on the web.
Other examples include Web accessibility a set of guidelines  and two accessible web portals designed for people developing reading skills are peepo.com  &m dash; try typing a letter with your keyboard for more &m dash; and peepo.co.UK  with enhanced graphics, unique style controls and improved interactivity (requires an SVG supported browser).
An alternative approach where users want to access public computer based terminals in Libraries, ATM, Information kiosks etc is for the user to present a token to the computer terminal, such as a smart card, that has configuration information to adjust the computer speed, text size, etc to their particular needs. The concept is encompassed by the CEN EN 1332-4 Identification Card Systems - Man-Machine Interface. This development of this standard has been supported in Europe by SNAPI and has been successfully incorporated into the Lasseo specifications .