HAL (software)

HAL (Hardware Abstraction Layer or rather Hardware Annotation Library) is a software subsystem for UNIX-like operating systems providing hardware abstraction.

HAL is now deprecated on most Linux distributions and on FreeBSD. Functionality is being merged into udev on Linux as of 2008–2010 and devd on FreeBSD. Previously, HAL was built on top of udev.

Some other OS-es which don't have an alternative like udev or devd, still use HAL.

The purpose of the hardware abstraction layer was to allow desktop applications to discover and use the hardware of the host system through a simple, portable and abstract API, regardless of the type of the underlying hardware.

HAL for Linux OS was originally envisioned by Havoc Pennington. It became a freedesktop.org project, and was a key part of the software stack of the GNOME and KDE desktop environments. It is free software, dual-licensed under both the GNU General Public License and the Academic Free License.

HAL is unrelated to the concept of Windows NT kernel HALs, which handle some platform-specific core functionality within the kernel, such as interrupt routing.

Traditionally, the operating system kernel was responsible for providing an abstract interface to the hardware the system ran on. Applications used the system call interface, or performed file I/O on device nodes in order to communicate with hardware through these abstractions. This sufficed for the simple hardware of early desktop computing.