Hardware Abstraction Layer
Hardware Abstraction Layer
A "Hardware Abstraction Layer" or HAL is an abstraction of the actual hardware, so as to present a consistent interface to software even if the underlying hardware alters or different models of the same device class vary a great deal in their implementation and actual interface. A HAL allows programmers to write device drivers in a consistent and largely model / brand agnostic manner, it might even isolate the kernel from much of the installed hardware. Operating systems which make use of a HAL will rarely, if ever, permit user-level software to interface directly with hardware devices and usually will not allow device drivers (which frequently run with privileges) to do so either.
Operating Systems known to use a HAL
The most prominent example of HAL usage is probably the NT series of operating systems from Microsft; this includes everything from at least Windows NT 4.0 through Windows 2000, Windows XP, Windows Vista upto and including Windows 7.