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Computer software (or simply software) refers to one or more computer programs held in the storage of a computer for some purpose. Program software performs the function of the program it implements, either by directly providing instructions to the computer hardware or by serving as input to another piece of software.
The term software was first used in this sense by John W. Tukey in 1957; colloquially, the term is often used to mean application software. In computer science and software engineering, computer software is all information processed by computer system, programs and data.
Computer software is so called in contrast to computer hardware, which is the physical substrate which stores and executes (or "runs") the software.
For other uses of the word software see Software (disambiguation).
System and application software
Computer science divides software into two major classes: system software and application software.
System software helps run the computer hardware and computer system. It includes operating systems, device drivers, programming tools, servers, windowing systems, utilities and more.
Application software allows a user to accomplish one or more specific tasks. Typical applications include office suites, business software, educational software, databases and computer games. Most of application software has GUIs.
Users see three layers of software
Users often see things differently than programmers. People who use modern general purpose computers (as opposed to embedded systems) usually see three layers of software performing a variety of tasks: platform, application, and user software.
- Platform software
Platform includes the basic input-output system (often described as firmware rather than software), device drivers, an operating system, and typically a graphical user interface which, in total, allow a user to interact with the computer and its peripherals (associated equipment). Platform software often comes bundled with the computer, and users may not realize that it exists or that they have a choice to use different platform software.
- Application software
Applications are what most people think of when they think of software. Typical examples include office suites and video games. Application software is often purchased separately from computer hardware. Sometimes applications are bundled with the computer, but that does not change the fact that they run as independent applications. Applications are almost always independent programs from the operating system, though they are often tailored for specific platforms. Most users think of compilers, databases, and other "system software" as applications.
- User-written software
User software tailors systems to meet the users specific needs. User software include spreadsheet templates, word processor macros, scientific simulations, graphics and animation scripts. Even email filters are a kind of user software. Users create this software themselves and often overlook how important it is.
See also: Three-tier application, Software architecture.
Software in operation
Computer software has to be "loaded" into the computer's storage (also known as memory and RAM).
Once the software is loaded, the computer is able to operate the software. Computers operate by executing the computer program. This involves passing instructions from the application software, through the system software, to the hardware which ultimately receives the instruction as machine code. Each instruction causes the computer to carry out an operation -- moving data, carrying out a computation, or altering the flow of instructions.
Kinds of software by operation: computer program as executable, source code or script, configuration.
Software is created with programming languages and related utilities, which may come in several of the above forms: single programs like script interpreters, packages containing a compiler, linker, and other tools; and large suites (often called Integrated Development Environments) that include editors, debuggers, and other tools for multiple languages.
The issue of software patents is very controversial, since while patents protect the ideas of "inventors", they are widely believed to hinder software development.