Computer software or simply software is any set of machine-readable instructions that directs a computer‘s processor to perform specific operations. Computer software is non-tangible, contrasted with computer hardware, which is the physical component of computers. Computer hardware and software require each other and neither can be realistically used without the other.
At the lowest level, executable code consists of machine language instructions specific to an individual processor—typically a central processing unit (CPU). Amachine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state. For example, an instruction may change the value stored in a particular storage location inside the computer—an effect that is not directly observable to the user. An instruction may also (indirectly) cause something to appear on a display of the computer system—a state change which should be visible to the user. The processor carries out the instructions in the order they are provided, unless it is instructed to “jump” to a different instruction, or interrupted.
Software written in a machine language is known as “machine code”. However, in practice, software is usually written in high-level programming languages that are easier and more efficient for humans to use (closer to natural language) than machine language. High-level languages are translated into machine language using a compiler or an interpreter or a combination of the two. Software may also be written in a low-level assembly language, essentially, a vaguely mnemonicrepresentation of a machine language using a natural language alphabet. Assembly language is translated into machine language using an assembler.
An outline (algorithm) for what would have been the first piece of software was written by Ada Lovelace in the 19th century, for the planned analytical engine. However, neither the analytical engine nor any software for it were ever created.
The first theory about software—prior to the creation of computers as we know them today—was proposed by Alan Turing in his 1935 essay Computable numbers with an application to the Entscheidungsproblem (decision problem).
This eventually led to the creation of the twin academic fields of computer science and software engineering, which both study software and its creation. Computer science is more theoretical (Turing’s essay is an example of computer science), whereas software engineering is focused on more practical concerns.
However, prior to 1946, software as we now understand it—programs stored in the memory of stored-program digital computers—did not yet exist. The very first electronic computing devices were instead rewired in order to “reprogram” them.
Design and implementation of software varies depending on the complexity of the software. For instance, the design and creation of Microsoft Word took much more time than designing and developing Microsoft Notepad because the latter has much more basic functionality.
Software is usually designed and created (a.k.a. coded/written/programmed) in integrated development environments (IDE) like Eclipse, IntelliJ and Microsoft Visual Studio that can simplify the process and compile the software (if applicable). As noted in a different section, software is usually created on top of existing software and the application programming interface (API) that the underlying software provides like GTK+, JavaBeans or Swing. Libraries (APIs) can be categorized by their purpose. For instance, the Spring Framework is used for implementing enterprise applications, the Windows Forms library is used for designing graphical user interface (GUI) applications like Microsoft Word, and Windows Communication Foundation is used for designing web services. When a program is designed, it relies upon the API. For instance, if a user is designing a Microsoft Windows desktop application, he or she might use the .NET Windows Forms library to design the desktop application and call its APIs like Form1.Close() and Form1.Show() to close or open the application, and write the additional operations him/herself that it needs to have. Without these APIs, the programmer needs to write these APIs him/herself. Companies like Oracle and Microsoft provide their own APIs so that many applications are written using their software libraries that usually have numerous APIs in them.
A person who creates software is called a programmer, software engineer or software developer, terms that all have a similar meaning. More informal terms for programmer also exist such as “coder” and “hacker” – although use of the latter word may cause confusion, because it is more often used to mean someone who illegally breaks into computer systems.