A 'computer program' is a collection of instructions that describes a task, or set of tasks, to be carried out by a
computer. More formally, it can be described as an expression of a ''computational method'' written in a
computer language.
[1]
Computer programs, also known as
software, may be categorized along functional lines. These functional categories include ''
application software'', ''
operating systems'', ''
video games'', and ''
compilers'', among others. Computer programs
embedded in hardware devices are called ''
firmware''.
The formal expression of computational methods in a human-readable computer language is often referred to as
source code, while the
machine-executable expressions of computational methods are commonly referred to as ''executables'', ''
object code'', or simply as ''
binaries'' — a reference to the
binary file format commonly used to store the executable code.
Terminology
Commercial computer programs aimed at
end users are commonly referred to as
application software by the computer industry, as these programs are focused on the functionality of what the computer is being used ''for'' (its ''application''), as opposed to being focused on system-level functionality (for example, as the
Windows operating system is). In practice, colloquially, both application software and system software may correctly be referred to as ''programs'', as may the more esoteric
firmware — software firmly built into an
embedded system.
Program execution
A ''computer program'' exists in a
source code form, viewable as a
programming language; as a tokenised form, ready to be
interpreted; or in
machine code form, ready to be executed. (An aside: source code form may also be interpreted.) Computer programs can be divided into two categories —
system software and
application software. ''System software'' is the
operating system that couples the
computer's hardware with the application software. ''Application software'' couples the system software with the
user interface.
A computer program is loaded into memory (usually by the operating system) and then
executed ("run"), instruction by instruction, until
termination, either with success or through software or hardware error.
Before a computer can execute any sort of program (including the operating system, itself a program), the computer hardware must be initialized. This initialization is done in modern
PCs by a piece of software stored on
programmable memory chips installed by the manufacturer, called the
BIOS. The BIOS will attempt to initialize the
boot sequence, making the computer ready for higher-level program execution.
Programs vs. data
The executable form of a program (that is, usually
object code) is often treated as being different from the
data the program operates on. In some cases this distinction is blurred with programs creating, or modifying, data, which is subsequently executed as part of the same program (this is a common occurrence for programs written in
Lisp), see
self-modifying code.
Programming
Computer programming is the iterative process of writing or editing
source code, followed by testing, analyzing and refining this code. A person who practices this skill is referred to as a computer
programmer or software developer. The sometimes lengthy process of computer programming is usually referred to as ''software development'', with the term ''
software engineering'' becoming more popular as the process comes to be seen as an
engineering discipline.
One approach to this process is
team programming, in which each member of the group has equal say in the development process, except for one person who guides the group through discrepancies. Another approach is referred to as ''peer programming'' or
pair programming.
A program is likely to contain a variety of
data structures and a variety of different
algorithms to operate on them.
Programming languages
Computer programs are often written by people (known as
computer programmers), but may also be generated by other programs - an example of
metaprogramming.
Various
programming paradigms can be employed in software development. The source code of most computer programs consists of a list of instructions that explicitly implement an
algorithm (known as an
imperative programming style); in another form (known as
declarative programming) the characteristics of the required information are specified and the method used to obtain the results, if any, is left to the
platform.
Examples of programming languages include
C,
JavaScript, and
Lisp.
Computational methods and algorithms
''Computational methods'' are a
superset of
algorithms, and adhere to most of the characteristics of algorithms:
#A computational method must be 'definite', meaning each step of the algorithm must be precisely defined. Formally defined computer languages meet this criteria by allowing algorithms to be specified in such a way that every statement has a very definite meaning.
#A computational method must have zero or more 'inputs', or quantities given to it before the algorithm runs.
#A computational method must have one or more 'outputs' which are quantities produced by the method, and will bear some specified relation to the inputs.
#A computational method is generally expected to be 'effective', meaning that its operations can be performed by hand, accurately and exactly, in a finite amount of time.
Although algorithms are defined to be 'finite', meaning they must complete in a finite number of steps, computational methods do not have to adhere to this restriction. A computational method theoretically does not have to stop running. Non-finite processes are common in ''reactive processes'', such as operating systems that continually interact with their environment.
[2]
References
1. "An expression of a computational method in a computer language is called a ''program''." The Art of Computer Programming, Volume 1, 3rd Edition, , Donald E., Knuth, Addison-Wesley, , ISBN 0-201-89683-4
2. The Art of Computer Programming, Volume 1, 3rd Edition, , Donald E., Knuth, Addison-Wesley, , ISBN 0-201-89683-4
Further reading
★
The Art of Computer Programming, Vol. 2, 3rd Ed, , Donald E., Knuth, Addison-Wesley, 1997, ISBN 0-201-89684-2
★
The Art of Computer Programming, Vol. 3, 3rd Ed, , Donald E., Knuth, Addison-Wesley, 1997, ISBN 0-201-89685-0
External links
★
Definition of "Program" at Webopedia
★
Definition of "Computer program" at Agtivity
★
Definition of "Software" at
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