Execution (computing)

Execution in computer and software engineering is the process by which a computer or a virtual machine performs the instructions of a computer program. The instructions in the program trigger sequences of simple actions on the executing machine. Those actions produce effects according to the semantics of the instructions in the program.

Programs for a computer may execute in a batch process without human interaction, or a user may type commands in an interactive session of an interpreter. In this case the "commands" are simply programs, whose execution is chained together.

The term run is used almost synonymously. A related meaning of both "to run" and "to execute" refers to the specific action of a user starting (or launching or invoking) a program, as in "Please run the application."

The context in which execution takes place is crucial. Very few programs execute on a bare machine. Programs usually contain implicit and explicit assumptions about resources available at the time of execution. Most programs execute with the support of an operating system and run-time libraries specific to the source language that provide crucial services not supplied directly by the computer itself. This supportive environment, for instance, usually decouples a program from direct manipulation of the computer peripherals, providing more general, abstract services instead.

Prior to execution, a program must first be written. This is generally done in source code, which is then compiled at compile time (and statically linked at link time) to an executable. This executable is then invoked, most often by an operating system, which loads the program into memory (load time), possibly performs dynamic linking, and then begins execution by moving control to the entry point of the program; all these steps depend on the Application Binary Interface of the operating system. At this point execution begins and the program enters run time. The program then runs until it ends, either normal termination or a crash.

...
Wikipedia