process states - TarisMajor/5143-OpSystems GitHub Wiki

Definition

In an operating system, Process States refer to the various stages or conditions in which a process can exist during its lifetime. These states describe the current status of a process as it progresses through its execution. A process transitions between these states based on external events like CPU availability, I/O operations, or user input.

The five primary process states are: New: The process is being created. At this stage, the operating system is preparing the resources required for the process, like memory and input/output buffers. Ready: The process is loaded into memory and is ready to execute, but it is waiting for CPU time. The process is in a queue awaiting its turn to be scheduled by the operating system. Running: The process is currently being executed by the CPU. It is actively performing its tasks. Waiting (Blocked): The process is waiting for some event to occur, such as the completion of I/O operations, or waiting for a resource to become available. It cannot proceed until the event occurs. Terminated (Exit): The process has completed its execution, or it has been terminated due to an error, or by a signal from another process. The operating system deallocates the resources associated with it. Inventor and Year of Invention The concept of process states emerged with the development of multitasking operating systems in the early 1960s. The idea was to manage the execution of multiple processes and optimize the use of CPU time, particularly in systems that used time-sharing or batch processing.

Historical Context:

1960s: Early operating systems like CTSS (Compatible Time-Sharing System) at MIT, developed in the early 1960s, and later Multics in the 1960s and 1970s, introduced the fundamental principles of process management, which included defining and managing process states. 1970s: The term "process state" and related concepts were formalized as part of the process scheduling algorithms in systems like Unix (developed at AT&T Bell Labs, 1971), which is one of the most influential operating systems. Thus, while no single inventor is credited with the "process state" concept, it evolved as part of the foundational work on operating system process management by researchers at MIT, Bell Labs, and other institutions during the 1960s and 1970s.

Uses

Process states are critical for an operating system to manage and schedule processes efficiently. These states help the operating system:

Schedule Processes: The operating system can use the process states to determine which processes should be running at any given time and which should be waiting for resources or events. Resource Management: By tracking the state of each process, the operating system ensures that resources like CPU time and memory are allocated optimally and without conflicts. Concurrency Management: Managing process states helps the operating system coordinate multiple processes concurrently and prevent issues like deadlocks, starvation, and race conditions. Examples of Where It Is Used Today Multitasking Operating Systems: In modern operating systems like Windows, Linux, and macOS, process states are used to manage the execution of multiple applications. For example, when you run multiple programs (web browsers, word processors, and music players), each program runs in its own process, which the operating system tracks through these states.

Ready State: When you launch a new program, it enters the "Ready" state until the CPU scheduler assigns it processor time. Running State: If the program is actively processing data or displaying information, it is in the "Running" state. Waiting State: If the program is waiting for an external event (like a file to load or user input), it will be in the "Waiting" state. Real-Time Systems: Real-time operating systems (RTOS) use process states to guarantee that time-critical tasks are processed in a timely manner. For instance, in medical devices like pacemakers or in automotive systems like airbags, the system uses process states to ensure that high-priority tasks are executed promptly.

Running State: A critical process that needs immediate CPU attention (such as an emergency stop function in a vehicle) may be in the "Running" state. Waiting State: If the system is waiting for sensor input, it might enter the "Waiting" state until it receives the necessary data. Server Systems: In web servers or database systems, processes are often in a "Waiting" state while waiting for a client request or for an I/O operation to complete. The operating system efficiently switches between processes based on their state, ensuring high concurrency and responsiveness.

Ready State: A web server process might be ready to process new requests when a client connects. Running State: Once a request is received, the server process enters the "Running" state to process the request. Gaming: Video games with complex tasks, such as rendering, physics simulation, and AI, often use process states to manage the different tasks concurrently. For example, the game might have a process in the "Waiting" state while loading assets, and once loading is complete, the process transitions to the "Ready" or "Running" state.

Embedded Systems: In embedded systems like industrial controllers or IoT devices, process states are used to manage multiple threads or processes concurrently. A process in an embedded system may switch between states based on input from sensors or network events.

Conclusion

Process states are an essential part of process management in modern operating systems. They allow the OS to track the status of each process and manage resources efficiently. By categorizing processes into various states, the operating system can ensure smooth multitasking, prevent conflicts, and optimize the performance of applications. This fundamental concept remains relevant in all modern computing environments, from personal computers to mobile devices and real-time systems.

Sources

Tanenbaum, A. S., & Woodhull, D. J. (2009). Operating Systems: Design and Implementation (3rd ed.). Prentice Hall. Silberschatz, A., Galvin, P. B., & Gagne, G. (2018). Operating System Concepts (9th ed.). Wiley. Stallings, W. (2017). Operating Systems: Internals and Design Principles (9th ed.). Pearson Education.