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A hardware abstraction layer (HAL) is an abstraction layer
Abstraction layer

An abstraction layer is a way of hiding the implementation details of a particular set of functionality. Software models that use layers of abstraction include the OSI model for computer network Protocol , the OpenGL graphics drawing library, and the byte stream input/output model originated by Unix and adopted by MSDOS, Linux, and most ot...
, implemented in software, between the physical hardware
Computer hardware

A personal computer is made up of computer hardware, multiple physical components onto which can be loaded into a multitude of software that perform the functions of the computer....
 of a computer
Computer

A computer is a machine that manipulates Data according to a list of Code .The first devices that resemble modern computers date to the mid-20th century , although the computer concept and various machines similar to computers existed earlier....
 and the software
Computer software

Computer software, or just software is a general term used to describe a collection of computer programs, Algorithm and Software documentation that perform some tasks on a computer system....
 that runs on that computer. Its function is to hide differences in hardware from most of the operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
 kernel, so that most of the kernel-mode code does not need to be changed to run on systems with different hardware. On a PC, HAL can basically be considered to be the driver for the motherboard and allows instructions from higher level computer languages to communicate with lower level components, such as directly with hardware.

The Windows NT
Windows NT

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix....
 operating system has a HAL in the kernel space, between hardware and kernel, drivers, executive services.






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A hardware abstraction layer (HAL) is an abstraction layer
Abstraction layer

An abstraction layer is a way of hiding the implementation details of a particular set of functionality. Software models that use layers of abstraction include the OSI model for computer network Protocol , the OpenGL graphics drawing library, and the byte stream input/output model originated by Unix and adopted by MSDOS, Linux, and most ot...
, implemented in software, between the physical hardware
Computer hardware

A personal computer is made up of computer hardware, multiple physical components onto which can be loaded into a multitude of software that perform the functions of the computer....
 of a computer
Computer

A computer is a machine that manipulates Data according to a list of Code .The first devices that resemble modern computers date to the mid-20th century , although the computer concept and various machines similar to computers existed earlier....
 and the software
Computer software

Computer software, or just software is a general term used to describe a collection of computer programs, Algorithm and Software documentation that perform some tasks on a computer system....
 that runs on that computer. Its function is to hide differences in hardware from most of the operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
 kernel, so that most of the kernel-mode code does not need to be changed to run on systems with different hardware. On a PC, HAL can basically be considered to be the driver for the motherboard and allows instructions from higher level computer languages to communicate with lower level components, such as directly with hardware.

The Windows NT
Windows NT

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix....
 operating system has a HAL in the kernel space, between hardware and kernel, drivers, executive services. This allows portability of the Windows NT kernel-mode code to a variety of processors, with different memory management unit
Memory management unit

A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to computer memory requested by the central processing unit ....
 architectures, and a variety of systems with different I/O bus architectures; most of that code runs without change on those systems, when compiled for the instruction set
Instruction set

An instruction set is a list of all the instruction , and all their variations, that a processor can execute.Instructions include:* Arithmetic such as add and subtract...
 for those systems. For example, the SGI
Silicon Graphics

Silicon Graphics, Inc. is a company manufacturer high-performance computing solutions, including computer hardware and computer software. SGI was founded by James H....
 Intel x86-based workstations were not IBM PC compatible
IBM PC compatible

IBM PC compatible computers are those generally similar to the original IBM Personal Computer, IBM Personal Computer XT, and IBM Personal Computer/AT....
 workstations, but due to the HAL, Windows NT was able to run on them.

BSD, Mac OS X
Mac OS X

Mac OS X is a line of computer operating systems developed, marketed, and sold by Apple Inc., and since 2002 has been included with all new Macintosh computer systems....
, Linux
Linux

Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL license...
, CP/M
CP/M

CP/M is an operating system originally created for Intel 8080/Intel 8085 based microcomputers by Gary Kildall of Digital Research. Initially confined to single tasking on 8-bit processors and no more than 64 kilobytes of memory, later versions of CP/M added multi-user variations, and were migrated to 16-bit processors....
, DOS
DOS

DOS, short for "Disk Operating System", is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions Windows 95, Windows 98, and Windows Me....
, Solaris, and some other portable operating systems also have a HAL, even if it's not explicitly designated as such. Some operating systems, such as Linux, have the ability to insert one while running, like Adeos
Adeos

Adeos is a nanokernel hardware abstraction layer that operates between computer hardware and the operating system that runs on it. It is distinct from other nanokernels, in that it is not just a low level layer for an outer kernel....
. The NetBSD
NetBSD

NetBSD is a freely redistributable, open source version of the Unix-derivative Berkeley Software Distribution computer operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed....
 operating system is widely known as having a clean hardware abstraction layer which allows it to be highly portable. As part of this system are /, , and other subsystems. Popular buses which are used on more than one architecture are also abstracted, such as ISA
Industry Standard Architecture

Industry Standard Architecture was a computer bus standard for IBM compatible computers....
, EISA
Extended Industry Standard Architecture

The Extended Industry Standard Architecture is a bus standard for IBM compatible computers. It was announced in late 1988 by IBM PC compatible vendors as a counter to IBM's use of its Proprietary software MicroChannel Architecture in its IBM Personal System/2 series....
, PCI
Peripheral Component Interconnect

The PCI Local Bus , or Conventional PCI, is a computer bus for attaching computer hardware in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification or an expansion card that fits into a socket....
, PCI-E, etc., allowing drivers to also be highly portable with a minimum of code modification.

An "extreme" example of a HAL can be found in the System/38
System/38

The System/38 was a midrange computer Server Platform manufactured and sold by the IBM Corporation. The system offered a number of innovative features, and was the brainchild of IBM engineer Frank Soltis....
 and AS/400 architecture. Most compilers for those systems generate an abstract machine code; the Licensed Internal Code, or LIC, translates this virtual machine code into native code for the processor on which it is running and executes the resulting native code. (The exceptions are compilers that generate the LIC itself; those compilers are not available outside IBM.) This was so successful that application software and operating system software above the LIC layer that were compiled on the original S/38 run without modification and without recompilation on the latest AS/400 systems, despite the fact that the underlying hardware has been changed dramatically; at least three different types of processors have been in use.

Hardware abstraction layers are of an even lower level in computer languages than application programming interface
Application programming interface

An application programming interface is a set of subroutine, data structures, class and/or Protocol provided by library and/or operating system Service s in order to support the building of applications....
s (API) because they interact directly with hardware
Hardware

Hardware is a general term that refers to the physical cultural artifacts of a technology. It may also mean the physical components of a computer system, in the form of computer hardware....
 instead of a system kernel, therefore HALs require less processing time than APIs. Higher level languages often use HALs and APIs to communicate with lower level components.

Operating systems having a defined HAL are easily portable across different hardware. This is especially important for embedded system
Embedded system

An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions, often with real-time computing constraints....
s that run on dozens of different platforms.

See also

  • HAL (software)
    HAL (software)

    In the field of Unix-like software, HAL, a hardware abstraction layer and software project developed by freedesktop.org, allows desktop applications running within an operating system to get ready access to information about Computer hardware so that they can locate and use such hardware regardless of Bus or Peripheral device....
  • Nanokernel