Process management (computing): Difference between revisions

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In any modern operating system, there can be more than one instance of a [[computer program|program]] loaded in memory at the same time. For example, more than one user can be executing the same program, with each user having separate copies of the program loaded into memory. With some programs, it is possible to have one copy loaded into memory, while several users have shared access to it so that they can each execute the same program-code. Such a program is called [[Reentrant (subroutine)|re-entrant]].{{Relevance inline|date=November 2023}} At a given instant, the [[central processing unit|processor]] can only be executing one instruction from one program, but several processes can be sustained over a period of time by assigning each process to the processor at intervals while the remainder become temporarily inactive. The execution of multiple processes over a period of time, rather than simultaneously, is known as concurrent execution.

A [[multiprogramming]] or [[Computer multitasking|multitasking]] OSO.S. is a systemOperating System that can execute many processes concurrently. Multiprogramming requires that the processor be allocated to each process for a period of time and de-allocated or issued at an appropriate moment. If the processor is de-allocated during the execution of a process, it must be done in a way that the process can restart later as efficiently as possible.

There are two waways for an OS to regain control of the processor during a program's execution in order for the OS to perform de-allocation or allocation:

# The process issues a [[system call]] (sometimes called a ''software [[interrupt]]''); for example, an I/O request occurs requesting to access a file on a hard disk.

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* Process Management Models, Scheduling, UNIX System V Release 4:

* Modern Operating Systems, Andrew Tanenbaum, Prentice Hall, (2nd Edition, 2001).

* Operating System Concepts, Silberschatz & Galvin & Gagne (httphttps://codex.cs.yale.edu/avi/os-book/OS9/slide-dir/), John Wiley & Sons, (6th Edition, 2003)

{{Operating System}}