Editing Process (computing) (section)

==History==
{{See also|History of operating systems}}

By the early 1960s, computer control software had evolved from [[monitor control software]], for example [[IBM 7090/94 IBSYS|IBSYS]], to [[executive control software]]. Over time, computers got faster while [[Time-sharing|computer time]] was still neither cheap nor fully utilized; such an environment made [[Computer multitasking#Multiprogramming|multiprogramming]] possible and necessary. Multiprogramming means that several programs run [[Concurrency (computer science)|concurrently]]. At first, more than one program ran on a single processor, as a result of underlying [[uniprocessor system|uniprocessor]] computer architecture, and they shared scarce and limited hardware resources; consequently, the concurrency was of a ''serial'' nature. On later systems with [[Multiprocessing|multiple processors]], multiple programs may run concurrently in ''[[Parallel computing|parallel]]''.

Programs consist of sequences of instructions for processors. A single processor can run only one instruction at a time: it is impossible to run more programs at the same time. A program might need some [[System resource|resource]], such as an input device, which has a large delay, or a program might start some slow operation, such as sending output to a printer. This would lead to processor being "idle" (unused). To keep the processor busy at all times, the execution of such a program is halted and the operating system switches the processor to run another program. To the user, it will appear that the programs run at the same time (hence the term "parallel").

Shortly thereafter, the notion of a "program" was expanded to the notion of an "executing program and its context". The concept of a process was born, which also became necessary with the invention of [[Reentrancy (computing)|re-entrant code]]. [[Thread (computer science)|Threads]] came somewhat later. However, with the advent of concepts such as [[time-sharing]], [[computer network]]s, and multiple-CPU [[shared memory]] computers, the old "multiprogramming" gave way to true [[Computer multitasking|multitasking]], [[multiprocessing]] and, later, [[Multithreading_(computer_architecture)|multithreading]].