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{{Short description|Developing programs for computer systems}}
{{More citations needed|date=November 2024}}
'''Systems programming''', or '''system programming''', is the activity of programming<ref name=":0" /> [[computer]] [[system software]]. The primary distinguishing characteristic of systems programming when compared to [[application programming]] is that application programming aims to produce software which provides services to the user directly (e.g. [[word processor]]), whereas systems programming aims to produce software and [[software platform]]s which provide services to other software, are performance constrained, or both (e.g. [[operating system]]s, [[computational science]] applications, [[game engine]]s, [[Automation#Industrial automation|industrial automation]], and [[software as a service]] applications).<ref name=":0">{{cite web|title=Panel: Systems Programming in 2014 and Beyond|url=https://channel9.msdn.com/Events/Lang-NEXT/Lang-NEXT-2014/Panel-Systems-Programming-Languages-in-2014-and-Beyond|publisher=Microsoft|access-date=4 December 2015}}</ref>

Systems programming requires a great degree of hardware awareness. Its goal is to achieve efficient use of available resources, either because the software itself is performance-critical or because even small efficiency improvements directly transform into significant savings of time or money.

== Overview ==

The following attributes characterize systems programming:
* The [[programmer]] can make assumptions about the hardware and other properties of the system that the program runs on, and will often exploit those properties, for example by using an [[algorithm]] that is known to be efficient when used with specific hardware.
* Usually a [[low-level programming language]] or programming language dialect is used so that:
** Programs can operate in resource-constrained environments
** Programs can be efficient with little [[Run-time system|runtime]] overhead, possibly having either a small [[runtime library]] or none at all
** Programs may use direct and "raw" control over memory access and [[control flow]]
** The programmer may write parts of the program directly in [[assembly language]]
* Often systems programs cannot be run in a [[debugger]]. Running the program in a [[computer simulation|simulated environment]] can sometimes be used to reduce this problem.{{Dubious|date=April 2024|reason=Most software built using contemporary programming languages can be run in a debugger, but it may not be acceptable to debug software in production or embedded systems.}}

In systems programming, often limited programming facilities are available. The use of [[garbage collection (computer science)|automatic garbage collection]] is not common and [[debugging]] is sometimes hard to do. The [[runtime library]], if available at all, is usually far less powerful, and does less error checking. Because of those limitations, [[System monitoring|monitoring]] and [[data logging|logging]] are often used; [[operating system]]s may have extremely elaborate logging subsystems.

Implementing certain parts in operating systems and networking requires systems programming, for example implementing paging ([[virtual memory]]) or a [[device driver]] for an operating system.

== History ==
Originally systems programmers invariably wrote in [[assembly language]]. Experiments with hardware support in [[high level languages]] in the late 1960s led to such languages as [[IBM PL/S|PL/S]], [[BLISS]], [[BCPL]], and extended [[ALGOL]] for [[Burroughs large systems]]. [[Forth (programming language)|Forth]] also has applications as a systems language.
In the 1970s, [[C (programming language)|C]] became widespread, aided by the growth of [[Unix]].
More recently a subset of [[C++]] called [[Embedded C++]] has seen some use, for instance it is used in the I/O Kit drivers of [[macOS]].<ref>{{cite web|author1=Apple Inc|title=I/O Kit Device Driver Design Guidelines|url=https://developer.apple.com/library/mac/documentation/DeviceDrivers/Conceptual/WritingDeviceDriver/CPluPlusRuntime/CPlusPlusRuntime.html#//apple_ref/doc/uid/TP30000695-BAJIBFDE|website=developer.apple.com|publisher=Apple Inc|access-date=16 September 2014|date=14 August 2009}}</ref>
Engineers working at [[Google]] created [[Go (programming language)|Go]] in 2007 to address developer productivity in large [[Distributed computing|distributed systems]], with developer-focused features such as [[Concurrency (computer science)|Concurrency]], [[Garbage collection (computer science)|Garbage Collection]], and faster program [[Compilation (computing)|compilation]] than C and C++.<ref>{{Cite web |title=Go at Google: Language Design in the Service of Software Engineering - The Go Programming Language |url=https://go.dev/talks/2012/splash.article |access-date=2024-04-11 |website=go.dev |language=en}}</ref>
In 2015 [[Rust (programming language)|Rust]] came out, a general-purpose programming language often used in systems programming. Rust was designed with memory safety in mind and to be as performant as C and C++.

== Alternative meaning ==
For historical reasons, some organizations use the term ''systems programmer'' to describe a job function which would be more accurately termed [[systems administrator]]. This is particularly true in organizations whose computer resources have historically been dominated by [[Mainframe computer|mainframe]]s, although the term is even used to describe job functions which do not involve mainframes. This usage arose because administration of [[IBM mainframes]] often involved the writing of custom [[assembler code]] ([[IBM Basic assembly language and successors|IBM's Basic Assembly Language]] (BAL)), which integrated with the [[operating system]] such as [[OS/MVS]], [[DOS/VSE]] or [[VM/CMS]]. Indeed, some [[IBM]] software products had substantial code contributions from customer programming staff. This type of programming is progressively less common, and increasingly done in C rather than Assembly, but the term ''systems programmer'' is still used as the de-facto job title for staff administering IBM mainframes even in cases where they do not regularly engage in systems programming activities.

== See also ==
* [[Ousterhout's dichotomy]]
* [[System programming language]]
* [[Scripting language]]
* [[Interrupt handler]]
* [[Computer programming|Computer Programming]]

== References ==
{{Reflist}}

==Further reading==
* [https://catalog.loc.gov/vwebv/holdingsInfo?&bibId=4177732 Systems Programming] by [[John J. Donovan]]

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{{DEFAULTSORT:Systems Programming}}
[[Category:Computer programming]]
[[Category:System software]]

Systems programming - Revision history

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