Process States in an Operating System: A Comprehensive Guide to Process Lifecycle

Understand the various states a process goes through during its lifetime in an operating system. This tutorial explains common process states (running, ready, blocked, etc.), the transitions between states, and the operating system's role in managing process lifecycles.

Process States in an Operating System

Process State Transitions

A process goes through various states during its lifetime, from creation to termination. While the exact names of states might vary slightly between operating systems, the fundamental states and transitions remain similar. A process can only be in one state at any given time.

Diagram showing process state transitions
  1. New: A new process is being created; it's not yet ready to run.
  2. Ready: The process is in main memory and ready to run, but waiting for CPU time. Many processes can be in the ready state at once.
  3. Running: The process is currently using the CPU. Only one process can be in the running state on a single-core system.
  4. Blocked/Waiting: The process is waiting for some event or resource (e.g., I/O, user input) before it can continue. The CPU is free to execute other processes.
  5. Terminated/Completed: The process has finished execution; its resources are released. The OS deletes the process's control block (PCB).
  6. Suspend Ready: The process is in a ready state but has been moved to secondary storage (e.g., hard drive) due to lack of main memory resources. It's moved back to the ready queue when memory becomes available.
  7. Suspend Wait: The process is blocked (waiting for a resource) and has been moved to secondary storage to free up main memory. It resumes execution once the needed resource is available and memory is allocated.

Operations on Processes

The operating system performs several key operations on processes during their lifecycle:

  1. Creation: A new process is created and added to the ready queue.
  2. Scheduling: The OS selects a process from the ready queue to run on the CPU.
  3. Execution: The CPU executes the instructions of the scheduled process; this may involve transitions to waiting/blocked states.
  4. Termination/Deletion: The process completes execution, or it is terminated by the OS. The OS reclaims the process's resources and removes its PCB.