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. To date, there has been a significant disparity in the accessibility of operating systems' APIs. As long as the API provides the means for delivering these and other accessibility features, applications within that environment can easily be made accessible by software application developers. 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 easily be customized by the user. It is important that the API provide support for accessibility. The API provides a set of building blocks, which programmers assemble into an application. All programs developed using a common API will have a similar interface, which makes applications easier to learn and use. 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.
However, a variety of graphic desktop environments have been developed for these operating systems and, consequently, have erected barriers for nonmousers and nonsighted users. The latter two operating systems both have strong command-based traditions that linger today, and assistive technologies that support their command-line interfaces have long been available. UNIX and Linux (an open-source UNIX-like operating system) are also widely used, particularly in higher education. In education, the most common graphic operating systems today are Microsoft's Windows and Apple's Mac OS.
However, as operating systems became increasingly graphics-oriented, accessibility barriers increased for individuals who couldn't see the graphics or use a mouse. 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. The OS provides a software platform on top of which application programs can run.
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.
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