How does accessibility differ across operating systems?
Updated January 11th, 2013
On any computer, the operating system (OS) is the set of programs that performs basic tasks that are necessary for the computer to be functional. The OS provides a software platform on top of which application programs can run. Early operating systems, including Microsoft's Disk Operating System (DOS) and UNIX® (originally developed by Bell Labs; now an open specification licensed by The Open Group), posed few accessibility barriers for users of assistive technologies because they were text-based. However, operating systems today are very graphics-oriented, and hence accessibility barriers exist for individuals who cannot see the graphics or use a mouse.
In business, the most common graphic operating systems today are Microsoft's Windows (about 89% of all users) and Apple's Mac OS. UNIX and Linux (an open-source UNIX-like operating system) are also fairly widely used. Unix and Linux have strong command-based options and assistive technologies that support their command-line interfaces have long been available. However, a variety of graphic desktop environments have been developed for these operating systems and, consequently, have erected barriers for non-mousers and non-sighted users.
One role of the graphic operating system is to provide an application program interface (API) to programmers so they can write applications consistent with the operating environment. All programs developed using a common API will have a similar interface, which makes applications easier to learn and use. The API provides a set of building blocks, which programmers assemble into an application. It is important that the API provide support for accessibility. For example, all menus and controls in a graphic user interface should be accessible via keyboard, not just mouse, and should be displayed with a font and color scheme that can be easily customized by the user. As long as the API provides the means for delivering these and other accessibility features, applications within that environment can be easily made accessible by software application developers.
To date, there has been a significant disparity in the accessibility of operating systems' APIs. Microsoft addressed many of the accessibility problems of its Windows API fairly early on and provided developers with the tools to develop applications that were accessible. Most Windows applications, for example, are entirely operable via keyboard so a mouse isn't required by the user. Other graphic operating systems have failed to deliver comparable accessibility, particularly for non-mousing and non-visual users.
Basic Accessibility Features
Some assistive technology and other accessibility features come bundled with all operating systems, but typically these applications provide only a minimal level of accessibility, not the full set of features that many users require for equal access to the OS and its applications. The following are common built-in accessibility features across all operating systems:
- Keyboard customization allows users to adjust keyboard behavior so they can: A) press one key at a time in place of multi-key combinations; B) use the keyboard to control mouse movements; and C) change the length of time it takes for a keystroke to be registered.
- Display customization allows users to control the display contrast, font style and size, size of icons, and other display characteristics.
- Multimode alerts provides system alerts visually for users who can't hear auditory alerts.
In addition to these basic accessibility features, both Windows and Mac OS include basic screen magnification software (Magnifier and Zoom, respectively). Windows additionally provides a basic screen reader application (text-to-speech translator) called Narrator, along with built-in speech recognition software, which allows the user to control the computer through a series of voice commands. Mac OS X includes limited text-to-speech capabilities and speech recognition (voice command) through its , VoiceOver application.
Each of these products provides a basic level of access, but these applications fall far short of the more fully featured screen magnification and screen-reading applications that are available for Windows via third-party developers.
Microsoft also developed a standard by which applications could effectively communicate with assistive technologies. This standard, called Microsoft® Active Accessibility® (MSAA), has been available since Windows 95. These early efforts to support accessibility, combined with the market dominance of Windows, led to a disproportionate number of assistive technologies being developed for Windows.
Microsoft UI Automation is the new accessibility framework for Microsoft Windows, available on all operating systems that support Windows Presentation Foundation (WPF). UI Automation provides programmatic access to most user interface (UI) elements on the desktop, enabling assistive technology products such as screen readers to provide information about the UI to end users and to manipulate the UI by means other than standard input.
In Windows 7, there is an "Ease of Access Center" that provides a convenient, centralized place to locate accessibility settings and programs to make your computer easier to use. The Ease of Access Center can be found in the Control Panel by selecting Windows logo key+U and also when logging into Windows.
The Microsoft Enable website includes detailed descriptions of accessibility features in current and previous releases of Microsoft Windows, step-by-step tutorials, and guides for users with specific disabilities.
With the release of Mac OS X, Apple improved the accessibility of its operating system. Mac OS X includes a screen magnification and VoiceOver, a screen-access technology, for the blind and visually impaired. To assist those with cognitive and learning disabilities, every Mac includes an alternative, simplified user interface that rewards exploration and learning. And, for those who find it difficult to use a mouse, every Mac computer includes Mouse Keys, Slow Keys, and Sticky Keys, which adapt the computer to the user’s needs and capabilities.
Apple has now built accessibility into its Carbon application programming interface (API), which allows Mac OS X applications to more effectively communicate with assistive technologies. Despite these efforts, however, there still are comparatively few assistive technology products available for Mac OS. For example, there is only one screen reading software option available, which has not provided the level of robustness of equivalent PC products. Additional information about Mac OS accessibility is provided on the Apple Accessibility website. This site includes specific steps for activating and using the accessibility features of Mac OS X.
Linux differs from both Windows and Mac OS in that it is an open source operating system and is supported and advanced by a dedicated community of developers. To date, the Linux developer community has produced a basic core set of accessibility features (as described above), as well as a combined screen reader/screen magnification application, Braille output software, and an on-screen keyboard. Each of these products was developed for the popular GNOME desktop, a graphic interface environment that runs on both Linux and Unix. Additional information about GNOME accessibility is available in the article Is Linux Accessible?.