Process Concept and Process States

An operating system (OS) is responsible for managing various tasks and processes within a computer system. The concept of a process is fundamental to understanding how an operating system handles concurrent execution of tasks.

What is a Process?

In simple terms, a process can be defined as an instance of a program in execution. It represents the basic unit of work within an operating system. Each process has its own memory space, program counter, and set of resources that are required to perform a specific task.

Processes can be independent or interdependent. Independent processes do not rely on each other and can execute concurrently. On the other hand, interdependent processes need to communicate and synchronize their actions to accomplish a common goal.

Process States

A process goes through several states during its lifetime. These states describe the current condition or situation of the process and determine its progress and behavior. The most commonly used process model is the "five-state process model", which includes the following states:

  1. New: In this state, the process is being created but has not yet been admitted to the pool of executable processes. The operating system performs various initialization tasks, such as allocating memory and other resources, before moving the process to the next state.

  2. Ready: A process in the ready state is loaded into the main memory and is waiting to be assigned to a processor for execution. However, it is important to note that being in the ready state does not guarantee immediate execution as the processor needs to schedule the process based on priority and other criteria.

  3. Running: Once a process is assigned to a processor, it enters the running state. In this state, the process starts executing its instructions, and the program counter keeps track of the next instruction to be executed. A process can stay in this state until it voluntarily releases the processor or until a higher-priority process preempts it.

  4. Blocked: When a process is unable to continue its execution due to the unavailability of a required resource or waiting for an event to occur, it enters the blocked state. For example, a process waiting for user input or for data to be read from disk would be in the blocked state. The process remains in this state until the event it is waiting for occurs, at which point it moves back to the ready state.

  5. Terminated: The terminated state represents the completion of a process. Once a process finishes its execution or is explicitly terminated by the user or the operating system, it enters this state. The OS will release the resources held by the terminated process and remove it from the system.

Process Transitions

Processes can transition between different states based on specific events or actions. The typical state transitions are as follows:

  • New to Ready: The process is created and moves to the ready state.
  • Ready to Running: The operating system scheduler selects the process from the ready queue and assigns it to a processor.
  • Running to Blocked: The process is waiting for an event or resource, such as user input or disk I/O, and is unable to continue execution.
  • Running to Ready: The process voluntarily releases the processor, or it is preempted by a higher-priority process.
  • Blocked to Ready: The event the process was waiting for has occurred, and it can resume execution after being placed back in the ready queue.
  • Running to Terminated: The process finishes its execution and enters the terminated state.

Understanding the different process states and their transitions is crucial for efficient task management within an operating system. It enables the OS to handle concurrent execution, prioritize processes, and ensure effective resource allocation, resulting in a smoother user experience and better overall system performance.

noob to master © copyleft