ExVar

ExVar is a Macintosh programming technology developed by Apple Computer in the 1980s. It was designed to allow developers to easily add device-specific code to Macintosh applications without having to rewrite the underlying software.

ExVar stands for External Variable, which refers to the operating system's ability to allow developers to add external code to the operating system's memory space. This allowed developers to create system extensions, device drivers, and other low-level software without having to modify the underlying Macintosh operating system.

One of the key goals of ExVar was to provide a way for developers to create third-party software that could interact with low-level hardware and system resources. This was seen as a way to increase the flexibility and customizability of the Macintosh platform.

ExVar was widely used during the 1980s and early 1990s, particularly for creating device drivers and system extensions for various peripherals and hardware devices. It was also used by some developers to create low-level utilities and diagnostic tools.

Over time, however, ExVar became less commonly used as Apple began to replace it with newer technologies such as Open Transport and Carbon. The release of Mac OS X in 2001 further reduced the need for ExVar as many of its functions were integrated into the new operating system.

Despite its limitations and eventual decline in use, ExVar remains an interesting chapter in the history of Macintosh programming and development. It played an important role in establishing the Macintosh as a flexible and customizable platform, and its legacy can still be seen in modern Macintosh operating systems.