Editing Computer program (section)

{{Short description|Instructions a computer can execute}}
{{for|the TV program|The Computer Programme{{!}}''The Computer Programme''}}
[[File:JavaScript_code.png|thumb|[[Source code]] for a computer program written in the [[JavaScript]] language. It demonstrates the ''appendChild'' method. The method adds a new child node to an existing parent node. It is commonly used to dynamically modify the structure of an HTML document.]]
{{Program execution}}
A '''computer program''' is a [[sequence]] or set{{efn|The [[Prolog]] language allows for a database of facts and rules to be entered in any order. However, a question about a database must be at the very end.}} of instructions in a [[programming language]] for a [[computer]] to [[Execution (computing)|execute]]. It is one component of [[software]], which also includes [[software documentation|documentation]] and other intangible components.<ref name="ISO 2020">{{cite web
 | title=ISO/IEC 2382:2015
 | website=ISO
 | date=2020-09-03
 | url=https://www.iso.org/obp/ui/#iso:std:iso-iec:2382:ed-1:v1:en
 | access-date=2022-05-26
 | quote=[Software includes] all or part of the programs, procedures, rules, and associated documentation of an information processing system.
 | archive-date=2016-06-17
 | archive-url=https://web.archive.org/web/20160617031837/https://www.iso.org/obp/ui/#iso:std:iso-iec:2382:ed-1:v1:en
 | url-status=live
 }}</ref>

A ''computer program'' in its [[human-readable]] form is called [[source code]]. Source code needs another computer program to [[Execution (computing)|execute]] because computers can only execute their native [[machine instructions]]. Therefore, source code may be [[Translator (computing)|translated]] to machine instructions using a [[compiler]] written for the language. ([[Assembly language]] programs are translated using an [[Assembler (computing)|assembler]].) The resulting file is called an [[executable]]. Alternatively, source code may execute within an [[interpreter (computing)|interpreter]] written for the language.<ref name="cpl_3rd-ch1-7_quoted">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 7
  | quote = An alternative to compiling a source program is to use an interpreter. An interpreter can directly execute a source program[.]
  | isbn = 0-201-71012-9
}}</ref>

If the executable is requested for execution, then the [[operating system]] [[Loader (computing)|loads]] it into [[Random-access memory|memory]] and starts a [[Process (computing)|process]].<ref name="osc-ch4-p98">{{cite book
  | last = Silberschatz
  | first = Abraham
  | title = Operating System Concepts, Fourth Edition
  | publisher = Addison-Wesley
  | year = 1994
  | page = 98
  | isbn = 978-0-201-50480-4
}}</ref> The [[central processing unit]] will soon [[Context switch|switch]] to this process so it can [[Instruction cycle|fetch, decode, and then execute]] each machine instruction.<ref name="sco-ch2-p32">{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/32 32]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/32
  }}</ref>

If the source code is requested for execution, then the operating system loads the corresponding interpreter into memory and starts a process. The interpreter then loads the source code into memory to translate and execute each [[Statement (computer science)|statement]]. Running the source code is slower than running an [[executable]].<ref name="cpl_3rd-ch1-7">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 7
  | isbn = 0-201-71012-9
}}</ref>{{efn|An executable has each [[machine instruction]] ready for the [[CPU]].}} Moreover, the interpreter must be installed on the computer.