In a multitasking computer system, processes may occupy a variety of states. These distinct states may not actually be recognized as such by the operating system kernel, however they are a useful abstraction for the understanding of processes. In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is... A BlueGene cabinet. ... In computing, a process is a running instance of a program, including all variables and other states. ... In information processing, a state is the complete set of properties (for example, its energy level, etc. ... An operating system (OS) is a computer program that manages the hardware and software resources of a computer. ... A kernel connects the software and hardware of a computer. ...

The various process states, displayed in a state diagram, with arrows indicating possible transitions between states - as can be seen, some processes are stored in main memory, and some are stored in secondary (virtual) memory.

Image File history File links Process_states. ... Image File history File links Process_states. ... State diagrams are used to graphically represent finite state machines. ...

Primary process states

The following typical process states are possible on computer systems of all kinds. In most of these states, processes are "stored" on main memory. It has been suggested that this article or section be merged with Physical memory. ...

Created

(Also called new.) When a process is first created, it occupies the "created" or "new" state. In this state, the process awaits admission to the "ready" state. This admission will be approved or delayed by a long-term, or admission, scheduler. Typically in most desktop computer systems, this admission will be approved automatically, however for real time operating systems this admission may be delayed. In a real time system, admitting too many processes to the "ready" state may lead to oversaturation and overcontention for the systems resources, leading to an inability to meet process deadlines. Look up scheduling in Wiktionary, the free dictionary. ... Desktop computer with several common peripherals (Monitor, keyboard, mouse, speakers, microphone and a printer) A desktop computer is a personal computer made for use on a desk in an office or home and is distinguished from portable computers such as laptops or PDAs and specialized computers such as servers. ... It has been suggested that Real-time computing be merged into this article or section. ... In telecommunication, the term contention has the following meanings: 1. ...

Ready

(Also called waiting or runnable.) A "ready" or "waiting" process has been loaded into main memory and is awaiting execution on a CPU (to be context switched onto the CPU by the dispatcher, or short-term scheduler). There may be many "ready" processes at any one point of the systems execution - for example, in a one processor system, only one process can be executing at any one time, and all other "concurrently executing" processes will be waiting for execution. It has been suggested that this article or section be merged with Physical memory. ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... A context switch is the computing process of storing and restoring the state (context) of a CPU such that multiple processes can share a single CPU resource. ...

Running

(Also called active or executing.) A "running", "executing" or "active" process is a process which is currently executing on a CPU. From this state the process may exceed its allocated time slice and be context switched out and back to "ready" by the operating system, it may indicate that it has finished and be terminated or it may block on some needed resource (such as an input / output resource) and be moved to a "blocked" state.

Blocked

(Also called sleeping.) Should a process "block" on a resource (such as a file, a semaphore or a device), it will be removed from the CPU (as a blocked process cannot continue execution) and will be in the blocked state. The process will remain "blocked" until its resource becomes available, which can unfortunately lead to deadlock. From the blocked state, the operating system may notify the process of the availability of the resource it is blocking on (the operating system itself may be alerted to the resource availability by an interrupt). Once the operating system is aware that a process is no longer blocking, the process is again "ready" and can from there be dispatched to its "running" state, and from there the process may make use of its newly available resource. A computer file is a collection of information that is stored in a computer system and can be identified by its full path name. ... A semaphore is a protected variable (or abstract data type) and constitutes the classic method for restricting access to equivalent shared resources (e. ... Look up device in Wiktionary, the free dictionary. ... A deadlock is a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does. ... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ...

Terminated

A process may be terminated, either from the "running" state by completing its execution or by explicitly being killed. In either of these cases, the process moves to the "terminated" state. If a process is not removed from memory after entering this state, this state may also be called zombie. An exit, when applied to computing, is when a process terminates execution. ... On Unix operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. ...

Additional process states

Two additional states are available for processes in systems that support virtual memory. In both of these states, processes are "stored" on secondary memory (typically a hard disk). It has been suggested that this article be split into multiple articles. ... Typical hard drives of the mid-1990s. ...

Swapped out and waiting

(Also called suspended and waiting.) In systems that support virtual memory, a process may be swapped out, that is removed from main memory and placed in virtual memory by the mid-term scheduler. From here the process may be swapped back into the waiting state.

Swapped out and blocked

(Also called suspended and blocked.) Processes that are blocked may also be swapped out. In this event the process is both swapped out and blocked, and may be swapped back in again under the same circumstances as a swapped out and waiting process (although in this case, the process will move to the blocked state, and may still be waiting for a resource to become available).

See also

• Multitasking
• Concurrency
• Process
• Thread
• Task
• Child process
• Orphan process
• Zombie process
• Context switch
• Scheduling
• Virtual memory

In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is... Wikiquote has a collection of quotations related to: Edsger Dijkstra The Dining Philosophers, a classic problem involving concurrency and shared resources In computer science, concurrency is a property of systems which consist of computations that execute overlapped in time, and which may permit the sharing of common resources between those... In computing, a process is a running instance of a program, including all variables and other state. ... A thread in computer science is short for a thread of execution. ... A task is an execution path through address space. In other words, a set of program instructions that is loaded in memory. ... A child process is a computer process created by another process (the parent process). ... A orphan process is a computer process whose Parent process has finished or terminated. ... On Unix operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. ... A context switch is the computing process of storing and restoring the state (context) of a CPU such that multiple processes can share a single CPU resource. ... Look up scheduling in Wiktionary, the free dictionary. ... It has been suggested that this article be split into multiple articles. ...

References