Editing Assembly language (section)

{{Short description|Low-level programming language family}}
{{Use dmy dates|date=March 2020|cs1-dates=y}}
{{Infobox programming language
| name = Assembly language
| logo = <!-- Filename only -->
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| screenshot = Motorola 6800 Assembly Language.png
| screenshot caption = Typical ''secondary output'' from an assembler&mdash;showing original assembly language (right) for the [[Motorola]] [[MC6800]] and the assembled form
| paradigm = [[Imperative programming|Imperative]], [[Unstructured programming|unstructured]], often [[metaprogramming]] (through [[Macro (computer science)|macros]]), certain assemblers are [[structured programming|structured]] or [[object-oriented programming|object-oriented]]
| family = 
| designer = <!-- or: | designers = -->
| developer = <!-- or: | developers = -->
| released = {{start date and age|1947|df=yes}}
| latest release version = 
| latest release date = <!-- {{start date and age|YYYY|MM|DD|df=yes}} -->
| typing = None
| scope = 
| programming language = 
| platform = 
| operating system = 
| license = 
| file ext = <code>.asm</code>, <code>.s</code>, <code>.S</code>, <code>.inc</code>, <code>.wla</code>, <code>.SRC</code> as well as several others depending on the assembler
| file format = <!-- or: | file formats = -->
| website = <!-- {{URL|www.example.com}} -->
| implementations = 
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}}

In [[computer programming]],  '''assembly language''' (alternatively '''assembler language'''<ref name="IBM_2014_ASM"/> or '''symbolic machine code'''),<ref name="Ohio_2016"/><ref name="Archer_2016"/><ref name="Streib 2020 p. ">{{cite book | last=Streib | first=James T. | title=Undergraduate Topics in Computer Science | chapter=Guide to Assembly Language | publisher=Springer International Publishing | publication-place=Cham | year=2020 | isbn=978-3-030-35638-5 | issn=1863-7310 | doi=10.1007/978-3-030-35639-2 | page= | s2cid=195930813 | quote=Programming in assembly language has the same benefits as programming in machine language, except it is easier.}}</ref> often referred to simply as '''assembly''' and commonly abbreviated as '''ASM''' or '''asm''', is any [[low-level programming language]] with a very strong correspondence between the instructions in the language and the [[computer architecture|architecture's]] [[machine code]] [[instruction set architecture|instructions]].<ref name="Saxon_1962"/> Assembly language usually has one [[Statement (computer science)|statement]] per machine instruction (1:1), but  constants, [[Comment (computer programming)|comments]], assembler [[Directive (programming)|directives]],<ref name="Kornelis_2010"/> symbolic [[Label (computer science)|labels]] of, e.g., [[memory location]]s, [[processor register|registers]], and [[Macro instruction|macros]]<ref name="IBM_2014_Macro"/><ref name="IBM_2014_ASM"/> are generally also supported.

The first assembly code in which a language is used to represent machine code instructions is found in [[Kathleen Booth|Kathleen]] and [[Andrew Donald Booth]]'s 1947 work, ''Coding for A.R.C.''.<ref>{{cite book |last1=Booth |first1=Andrew D |last2=Britten |first2=Kathleen HV |title=Coding for A.R.C. |date=1947 |publisher=Institute for Advanced Study, Princeton |url=https://albert.ias.edu/bitstream/handle/20.500.12111/7941/Booth_Britten_Coding_for_ARC_1947.pdf?sequence=1&isAllowed=y |access-date=4 November 2022}}</ref> Assembly code is converted into executable machine code by a [[Utility software|utility program]] referred to as an ''[[Assembler (computing)|assembler]]''. The term "assembler" is generally attributed to [[Maurice Wilkes|Wilkes]], [[David Wheeler (computer scientist)|Wheeler]] and [[Stanley Gill|Gill]] in their 1951 book ''[[The Preparation of Programs for an Electronic Digital Computer]]'',<ref name="Wilkes_1951"/> who, however, used the term to mean "a program that assembles another program consisting of several sections into a single program".<ref name="Fairhead_2017"/> The conversion process is referred to as ''assembly'', as in ''assembling'' the [[source code]]. The computational step when an assembler is processing a program is called ''assembly time''.

Because assembly depends on the machine code instructions, each assembly language<ref group=nb>Other than meta-assemblers</ref> is specific to a particular [[computer architecture]].<ref name="OS360_2011"/><ref name="Austerlitz 2003 pp. 326–360">{{cite book | last=Austerlitz | first=Howard | title=Data Acquisition Techniques Using PCs | chapter=Computer Programming Languages | publisher=Elsevier | year=2003 | doi=10.1016/b978-012068377-2/50013-9 | pages=326–360 | isbn=9780120683772 | quote=Assembly language (or Assembler) is a compiled, low-level computer language. It is processor-dependent since it basically translates the Assembler's mnemonics directly into the commands a particular CPU understands, on a one-to-one basis. These Assembler mnemonics are the instruction set for that processor.}}</ref><ref name="Carnes 2022">{{cite web |last=Carnes |first=Beau |date=2022-04-27 |title=Learn Assembly Language Programming with ARM |url=https://www.freecodecamp.org/news/learn-assembly-language-programming-with-arm/ |url-status=live |access-date=2022-06-21 |website=freeCodeCamp.org |language=en-US |quote=Assembly language is often specific to a particular computer architecture so there are multiple types of assembly languages. ARM is an increasingly popular assembly language.}}</ref>

Sometimes there is more than one assembler for the same architecture, and sometimes an assembler is specific to an [[operating system]] or to particular operating systems. Most assembly languages do not provide specific [[Syntax (programming languages)|syntax]] for operating system calls, and most assembly languages can be used universally with any operating system,<ref group=nb>However, that does not mean that the assembler programs implementing those languages are universal.</ref> as the language provides access to all the real capabilities of the [[Processor (computing)|processor]], upon which all [[system call]] mechanisms ultimately rest. In contrast to assembly languages, most [[high-level programming language]]s are generally [[porting|portable]] across multiple architectures but require [[Interpreter (computing)|interpreting]] or [[Compiler|compiling]], much more complicated tasks than assembling.

In the first decades of computing, it was commonplace for both [[systems programming]] and [[application programming]] to take place entirely in assembly language.  While still irreplaceable for some purposes, the majority of programming is now conducted in higher-level interpreted and compiled languages.  In "[[No Silver Bullet]]", [[Fred Brooks]] summarised the effects of the switch away from assembly language programming: "Surely the most powerful stroke for software productivity, reliability, and simplicity has been the progressive use of high-level languages for programming. Most observers credit that development with at least a factor of five in productivity, and with concomitant gains in reliability, simplicity, and comprehensibility."<ref name="Brooks_1986_NSB"/>

Today, it is typical to use small amounts of assembly language code within larger systems implemented in a higher-level language, for performance reasons or to interact directly with hardware in ways unsupported by the higher-level language.  For instance, just under 2% of version 4.9 of the [[Linux kernel]] source code is written in assembly; more than 97% is written in [[C (programming language)|C]].<ref name="Anguiano_kernel_sloccount">{{Cite web | author-last=Anguiano | author-first = Ricardo | title=linux kernel mainline 4.9 sloccount.txt |url=https://gist.github.com/ricardoanguiano/18125b7eb3f26cf83724fb60662bdd2c |access-date=2022-05-04 |website=Gist |language=en}}</ref>