Operating Systems | States of Process and Operations

A process from its creation to completion goes through various stages in order to complete the works defined on it. Each of these stages are known as states of a process.

States of a Process
  1. New

    It is a condition just before the transition from as a program in the secondary memory to a process in the main memory.

  2. Ready

    The processes which are ready on main memory and not forwarded(scheduling) into central processing system can be said in Ready state.

    There can be more one process present in ready state which will be allocated to processing unit. The order, in which each of them will get executed will depend on the nature of scheduling algorithm used. Basically scheduling algorithms are of two types:

    1. Preemptive algorithms : Scheduling algorithms with ability to suspend the process during the execution. Preemptive algorithms switches between process is also known as context switching, since PCB(context) has to be saved to resume preempted processes.
    2. Non preemptive algorithms : Scheduling algorithms which does not have the ability to suspend the process during its execution.

  3. Run

    Process which is scheduled to CPU is in Run state. A single core processor will be having one process in run state and multi-core processor may have more than one process in run state at time. CPU would be addressing focus boundary of a process in run state continuously.

  4. Block (or wait)

    (MM) Whenever there is a need of I/O during running of the process, it will switch to Block(or Wait) state and the completion of I/O will set back the process to ready state again.

  5. Termination

    Completion of execution of job defined in process turns the process to termination state, where the context get deleted and memory allocated to it will get deallocated.

  6. Suspend ready

    This state occurs when main memory is full and newly created process is of higher priority than existing processes, processes with lower priority has to be moved to the backup memory (on secondary memory). Normally decision of priority will be done by scheduler.

  7. Suspend wait (or suspend block)

    If the process which was send to backup memory(on secondary memory) was in wait or block mode for I/O operations then it is in suspend wait or suspend block state

Operations on Process
  1. CREATE : Creation of process by loading executable code of the program into main memory.
  2. SCHEDULE : Assigning process to CPU from the processes available in the main memory.
  3. EXECUTE : Running of process in the CPU.
  4. DELETE/KILLING : Deallocation of assigned memory for the creation due to completion of job.